• Adames, Á. F., and J. M. Wallace, 2014: Three-dimensional structure and evolution of the MJO and its relation to the mean flow. J. Atmos. Sci., 71, 20072026, doi:10.1175/JAS-D-13-0254.1.

    • Search Google Scholar
    • Export Citation
  • Agrawala, S., M. Barlow, H. Cullen, and B. Lyon, 2001: The drought and humanitarian crisis in central and southwest Asia: A climate perspective. IRI Rep. 0111, 24 pp.

  • Aizen, E. M., V. B. Aizen, J. M. Melack, T. Nakamura, and T. Ohta, 2001: Precipitation and atmospheric circulation patterns at mid-latitudes of Asia. Int. J. Climatol., 21, 535556, doi:10.1002/joc.626.

    • Search Google Scholar
    • Export Citation
  • Aizen, V. B., V. A. Kuzmichenok, A. B. Surazakov, and E. M. Aizen, 2006: Glacier changes in the central and northern Tien Shan during the last 140 years based on surface and remote-sensing data. Ann. Glaciol., 43, 202213, doi:10.3189/172756406781812465.

    • Search Google Scholar
    • Export Citation
  • Aizen, V. B., E. M. Aizen, and V. A. Kuzmichenok, 2007: Glaciers and hydrological changes in the Tien Shan: Simulation and prediction. Environ. Res. Lett., 2, 045019, doi:10.1088/1748-9326/2/4/045019.

    • Search Google Scholar
    • Export Citation
  • Alijani, B., 2008: Effect of the Zagros Mountains on the spatial distribution of precipitation. J. Mt. Sci., 5, 218231, doi:10.1007/s11629-008-0126-8.

    • Search Google Scholar
    • Export Citation
  • Almazroui, M., 2011: Calibration of TRMM rainfall climatology over Saudi Arabia during 1998–2009. Atmos. Res., 99, 400414, doi:10.1016/j.atmosres.2010.11.006.

    • Search Google Scholar
    • Export Citation
  • Almazroui, M., M. Nazrul Islam, H. Athar, P. D. Jones, and M. A. Rahman, 2012: Recent climate change in the Arabian Peninsula: Annual rainfall and temperature analysis of Saudi Arabia for 1978–2009. Int. J. Climatol., 32, 953966, doi:10.1002/joc.3446.

    • Search Google Scholar
    • Export Citation
  • Alpert, P., and Coauthors, 2002: The paradoxical increase of Mediterranean extreme daily rainfall in spite of decrease in total values. Geophys. Res. Lett., 29, 1536, doi:10.1029/2001GL013554.

    • Search Google Scholar
    • Export Citation
  • Al-Rawas, G., and C. Valeo, 2009: Characteristics of rainstorm temporal distributions in arid mountainous and coastal regions. J. Hydrol., 376, 318326, doi:10.1016/j.jhydrol.2009.07.044.

    • Search Google Scholar
    • Export Citation
  • AlSarmi, S., and R. Washington, 2011: Recent observed climate change over the Arabian Peninsula. J. Geophys. Res., 116, D11109, doi:10.1029/2010JD015459.

    • Search Google Scholar
    • Export Citation
  • AlSarmi, S., and R. Washington, 2014: Changes in climate extremes in the Arabian Peninsula: Analysis of daily data. Int. J. Climatol., 34, 13291345, doi:10.1002/joc.3772.

    • Search Google Scholar
    • Export Citation
  • Al Senafi, F., and A. Anis, 2015: Shamals and climate variability in the Northern Arabian/Persian Gulf from 1973 to 2012. Int. J. Climatol., 35, 45094528, doi:10.1002/joc.4302.

    • Search Google Scholar
    • Export Citation
  • Athar, H., 2015: Teleconnections and variability in observed rainfall over Saudi Arabia during 1978–2010. Atmos. Sci. Lett., 16, 373379, doi:10.1002/asl2.570.

    • Search Google Scholar
    • Export Citation
  • Avissar, R., and Y. Liu, 1996: Three-dimensional numerical study of shallow convective clouds and precipitation induced by land surface forcing. J. Geophys. Res., 101, 74997518, doi:10.1029/95JD03031.

    • Search Google Scholar
    • Export Citation
  • Barlow, M., 2011: Africa and west Asia. Intraseasonal Variability in the Coupled Tropical Ocean-Atmosphere System, W. Lau and D. Waliser, Eds., Praxis, 477–493.

    • Search Google Scholar
    • Export Citation
  • Barlow, M., and M. K. Tippett, 2008: Variability and predictability of central Asia river flows: Antecedent winter precipitation and large-scale teleconnections. J. Hydrometeor., 9, 13341349, doi:10.1175/2008JHM976.1.

    • Search Google Scholar
    • Export Citation
  • Barlow, M., H. Cullen, and B. Lyon, 2002: Drought in central and southwest Asia: La Niña, the warm pool, and Indian Ocean precipitation. J. Climate, 15, 697700, doi:10.1175/1520-0442(2002)015<0697:DICASA>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Barlow, M., M. Wheeler, B. Lyon, and H. Cullen, 2005: Modulation of daily precipitation over southwest Asia by the Madden–Julian oscillation. Mon. Wea. Rev., 133, 35793594, doi:10.1175/MWR3026.1.

    • Search Google Scholar
    • Export Citation
  • Barlow, M., H. Cullen, B. Lyon, and O. Wilhelmi, 2006: Drought disaster in Asia. Natural Disaster Hotspots: Case Studies, J. Arnold et al., Eds., World Bank, 1–19.

  • Barlow, M., A. Hoell, and F. Colby, 2007: Examining the wintertime response to tropical convection over the Indian Ocean by modifying convective heating in a full atmospheric model. Geophys. Res. Lett., 34, L19702, doi:10.1029/2007GL030043.

    • Search Google Scholar
    • Export Citation
  • Betts, A. K., and J. H. Ball, 1998: FIFE surface climate and site-average dataset 1987–89. J. Atmos. Sci., 55, 10911108, doi:10.1175/1520-0469(1998)055<1091:FSCASA>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Black, E., 2009: The impact of climate change on daily precipitation statistics in Jordan and Israel. Atmos. Sci. Lett., 10, 192200, doi:10.1002/asl.233.

    • Search Google Scholar
    • Export Citation
  • Black, E., 2012: The influence of the North Atlantic Oscillation and European circulation regimes on the daily to interannual variability of winter precipitation in Israel. Int. J. Climatol., 32, 16541664, doi:10.1002/joc.2383.

  • Black, E., D. J. Brayshaw, and C. M. C. Rambeau, 2010: Past, present and future precipitation in the Middle East: Insights from models and observations. Philos. Trans. Roy. Soc. London, 368A, 51735184, doi:10.1098/rsta.2010.0199.

    • Search Google Scholar
    • Export Citation
  • Blake, D. W., T. N. Krishnamurti, S. V. Low-Nam, and J. S. Fein, 1983: Heat low over the Saudi Arabian desert during May 1979 (Summer MONEX). Mon. Wea. Rev., 111, 17591775, doi:10.1175/1520-0493(1983)111<1759:HLOTSA>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Bollasina, M., and S. Nigam, 2011: Modeling of regional hydroclimate change over the Indian subcontinent: Impact of the expanding Thar Desert. J. Climate, 24, 30893106, doi:10.1175/2010JCLI3851.1.

    • Search Google Scholar
    • Export Citation
  • Bozkurt, D., O. L. Sen, and S. Hagemann, 2015: Projected river discharge in the Euphrates–Tigris basin from a hydrological discharge model forced with RCM and GCM outputs. Climate Res., 62, 131147, doi:10.3354/cr01268.

    • Search Google Scholar
    • Export Citation
  • Bruins, H. J., 1999: Drought management and water supply systems in Israel. Drought Management Planning in Water Supply Systems, E. Cabrera and J. García-Serra, Eds., Kluwer Academic Publishers, 299–321.

    • Search Google Scholar
    • Export Citation
  • Cannon, F., L. M. Carvalho, C. Jones, and J. Norris, 2016: Winter westerly disturbance dynamics and precipitation in the western Himalaya and Karakoram: A wave-tracking approach. Theor. Appl. Climatol., 125, 2744, doi:10.1007/s00704-015-1489-8.

    • Search Google Scholar
    • Export Citation
  • Centre for International Earth Science Information Network, 2005: Poverty mapping project: Global subnational infant mortality rates. NASA Socioeconomic Data and Applications Center, accessed 11 April 2014, doi:10.7927/H4PZ56R2.

  • Chakraborty, A., S. K. Behera, M. Mujumdar, R. Ohba, and T. Yamagata, 2006: Diagnosis of tropospheric moisture over Saudi Arabia and influences of IOD and ENSO. Mon. Wea. Rev., 134, 598617, doi:10.1175/MWR3085.1.

    • Search Google Scholar
    • Export Citation
  • Charabi, Y., and S. Al-Hatrushi, 2010: Synoptic aspects of winter rainfall variability in Oman. Atmos. Res., 95, 470486, doi:10.1016/j.atmosres.2009.11.009.

    • Search Google Scholar
    • Export Citation
  • Charney, J. G., 1975: Dynamics of deserts and drought in the Sahel. Quart. J. Roy. Meteor. Soc., 101, 193202, doi:10.1002/qj.49710142802.

    • Search Google Scholar
    • Export Citation
  • Christensen, J. H., and Coauthors, 2013: Climate phenomena and their relevance for future regional climate change. Climate Change 2013: The Physical Science Basis, T. F. Stocker et al., Eds., Cambridge University Press, 1217–1308. [Available online at http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/supplementary/WG1AR5_Ch14SM_FINAL.pdf.]

    • Search Google Scholar
    • Export Citation
  • Centre for Research on the Epidemiology of Disasters, 2014: EM-DAT: The OFDA/CRED international disaster database. Accessed 22 December 2014. [Available online at www.em-dat.be.]

  • Cullen, H. M., and P. B. deMenocal, 2000: North Atlantic influence on Tigris–Euphrates streamflow. Int. J. Climatol., 20, 853863, doi:10.1002/1097-0088(20000630)20:8<853::AID-JOC497>3.0.CO;2-M.

    • Search Google Scholar
    • Export Citation
  • Cullen, H. M., A. Kaplan, P. A. Arkin, and P. B. deMenocal, 2002: Impact of the North Atlantic Oscillation on Middle Eastern climate and streamflow. Climatic Change, 55, 315338, doi:10.1023/A:1020518305517.

    • Search Google Scholar
    • Export Citation
  • Dai, A., 2013: Increasing drought under global warming in observations and models. Nat. Climate Change, 3, 5258, doi:10.1038/nclimate1633.

    • Search Google Scholar
    • Export Citation
  • deMenocal, P. B., 2001: Cultural responses to climate change during the late Holocene. Science, 292, 667673, doi:10.1126/science.1059827.

    • Search Google Scholar
    • Export Citation
  • Diffenbaugh, N. S., M. Scherer, and M. Ashfaq, 2013: Response of snow-dependent hydrologic extremes to continued global warming. Nat. Climate Change, 3, 379384, doi:10.1038/nclimate1732.

    • Search Google Scholar
    • Export Citation
  • Dirmeyer, P. A., 1994: Vegetation stress as a feedback mechanism in midlatitude drought. J. Climate, 7, 14631483, doi:10.1175/1520-0442(1994)007<1463:VSAAFM>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Dirmeyer, P. A., and K. L. Brubaker, 2007: Characterization of the global hydrologic cycle from a back-trajectory analysis of atmospheric water vapor. J. Hydrometeor., 8, 2037, doi:10.1175/JHM557.1.

    • Search Google Scholar
    • Export Citation
  • Donat, M. G., and Coauthors, 2014: Changes in extreme temperature and precipitation in the Arab region: Long-term trends and variability related to ENSO and NAO. Int. J. Climatol., 34, 581592, doi:10.1002/joc.3707.

    • Search Google Scholar
    • Export Citation
  • Douville, H., J.-F. Royer, D. B. Stephenson, S. Tyteca, J. Polcher, P. Cox, N. Gedney, and P. Valdes, 2000: Impact of CO2 doubling on the Asian summer monsoon: Robust versus model-dependent responses. J. Meteor. Soc. Japan, 78, 421439.

    • Search Google Scholar
    • Export Citation
  • El Kharraz, J., A. El-Sadek, N. Ghaffour, and E. Mino, 2012: Water scarcity and drought in WANA countries. Procedia Eng., 33, 1429, doi:10.1016/j.proeng.2012.01.1172.

    • Search Google Scholar
    • Export Citation
  • Enzel, Y., R. Bookman, D. Sharon, H. Gvirtzman, U. Dayan, B. Ziv, and M. Stein, 2003: Late Holocene climates of the near east deduced from Dead Sea level variations and modern regional winter rainfall. Quat. Res., 60, 263273, doi:10.1016/j.yqres.2003.07.011.

    • Search Google Scholar
    • Export Citation
  • Evans, J. P., 2008: Changes in water vapor transport and the production of precipitation in the eastern Fertile Crescent as a result of global warming. J. Hydrometeor., 9, 13901401, doi:10.1175/2008JHM998.1.

    • Search Google Scholar
    • Export Citation
  • Evans, J. P., 2009: 21st century climate change in the Middle East. Climatic Change, 92, 417432, doi:10.1007/s10584-008-9438-5.

  • Evans, J. P., 2010: Global warming impact on the dominant precipitation processes in the Middle East. Theor. Appl. Climatol., 99, 389402, doi:10.1007/s00704-009-0151-8.

    • Search Google Scholar
    • Export Citation
  • Evans, J. P., and R. Geerken, 2004: Discrimination between climate and human-induced dryland degradation. J. Arid Environ., 57, 535554, doi:10.1016/S0140-1963(03)00121-6.

    • Search Google Scholar
    • Export Citation
  • Evans, J. P., and R. B. Smith, 2006: Water vapor transport and the production of precipitation in the eastern Fertile Crescent. J. Hydrometeor., 7, 12951307, doi:10.1175/JHM550.1.

    • Search Google Scholar
    • Export Citation
  • Evans, J. P., and B. F. Zaitchik, 2008: Modeling the large-scale water balance impact of different irrigation systems. Water Resour. Res., 44, W08448, doi:10.1029/2007WR006671.

  • Evans, J. P., and A. Alsamawi, 2011: The importance of the Zagros Mountains barrier jet to future precipitation in the Fertile Crescent. Open Atmos. Sci. J., 5, 8795, doi:10.2174/1874282301105010087.

    • Search Google Scholar
    • Export Citation
  • Evans, J. P., R. B. Smith, and R. J. Oglesby, 2004: Middle East climate simulation and dominant precipitation processes. Int. J. Climatol., 24, 16711694, doi:10.1002/joc.1084.

    • Search Google Scholar
    • Export Citation
  • Feldstein, S. B., and U. Dayan, 2008: Circumglobal teleconnections and wave packets associated with Israeli winter precipitation. Quart. J. Roy. Meteor. Soc., 134, 455467, doi:10.1002/qj.225.

    • Search Google Scholar
    • Export Citation
  • Flato, G., and Coauthors, 2013: Evaluation of climate models. Climate Change 2013: The Physical Science Basis, T. F. Stocker et al., Eds., Cambridge University Press, 741–866, doi:10.1017/CBO9781107415324.020.

    • Search Google Scholar
    • Export Citation
  • Fröhlich, C. J., 2013: Water: Reason for conflict or catalyst for peace? The case of the Middle East. L’Europe Form., 3, 139161.

  • Ganor, E., I. Osetinsky, A. Stupp, and P. Alpert, 2010: Increasing trend of African dust, over 49 years, in the eastern Mediterranean. J. Geophys. Res., 115, D07201, doi:10.1029/2009JD012500.

    • Search Google Scholar
    • Export Citation
  • Gessner, U., V. Naeimi, I. Klein, C. Kuenzer, D. Klein, and S. Dech, 2013: The relationship between precipitation anomalies and satellite-derived vegetation activity in central Asia. Global Planet. Change, 110, 7487, doi:10.1016/j.gloplacha.2012.09.007.

    • Search Google Scholar
    • Export Citation
  • Giannakopoulou, E. M., and R. Toumi, 2012: The Persian Gulf summertime low-level jet over sloping terrain. Quart. J. Roy. Meteor. Soc., 138, 145157, doi:10.1002/qj.901.

    • Search Google Scholar
    • Export Citation
  • Giorgi, F., and P. Lionello, 2008: Climate change projections for the Mediterranean region. Global Planet. Change, 63, 90104, doi:10.1016/j.gloplacha.2007.09.005.

    • Search Google Scholar
    • Export Citation
  • Gleick, P., 2014: Water, drought, climate change, and conflict in Syria. Wea. Climate Soc., 6, 331340, doi:10.1175/WCAS-D-13-00059.1.

    • Search Google Scholar
    • Export Citation
  • Golian, S., O. Mazdiyasni, A. AghaKouchak, 2015: Trends in meteorological and agricultural droughts in Iran. Theor. Appl. Climatol., 119, 679688, doi:10.1007/s00704-014-1139-6.

    • Search Google Scholar
    • Export Citation
  • Hartmann, D. L., and Coauthors, 2013: Observations: Atmosphere and surface. Climate Change 2013: The Physical Science Basis, T. F. Stocker et al., Eds., Cambridge University Press, 159–254.

  • Hoell, A., and C. Funk, 2013: The ENSO-related west Pacific sea surface temperature gradient. J. Climate, 26, 95459562, doi:10.1175/JCLI-D-12-00344.1.

    • Search Google Scholar
    • Export Citation
  • Hoell, A., M. Barlow, and R. Saini, 2012: The leading pattern of intraseasonal and interannual Indian Ocean precipitation variability and its relationship with Asian circulation during the boreal cold season. J. Climate, 25, 75097526, doi:10.1175/JCLI-D-11-00572.1.

    • Search Google Scholar
    • Export Citation
  • Hoell, A., M. Barlow, and R. Saini, 2013: Intraseasonal and seasonal-to-interannual Indian Ocean convection and hemispheric teleconnections. J. Climate, 26, 88508867, doi:10.1175/JCLI-D-12-00306.1.

    • Search Google Scholar
    • Export Citation
  • Hoell, A., C. Funk, and M. Barlow, 2014a: The regional forcing of Northern Hemisphere drought during recent warm tropical west Pacific Ocean La Niña events. Climate Dyn., 42, 32893311, doi:10.1007/s00382-013-1799-4.

    • Search Google Scholar
    • Export Citation
  • Hoell, A., C. Funk, and M. Barlow, 2014b: La Niña diversity and northwest Indian Ocean rim teleconnections. Climate Dyn., 43, 27072724, doi:10.1007/s00382-014-2083-y.

    • Search Google Scholar
    • Export Citation
  • Hoell, A., C. Funk, and M. Barlow, 2015: The forcing of southwestern Asia teleconnections by low-frequency sea surface temperature variability during boreal winter. J. Climate, 28, 15111526, doi:10.1175/JCLI-D-14-00344.1.

    • Search Google Scholar
    • Export Citation
  • Hoerling, M., and A. Kumar, 2003: The perfect ocean for drought. Science, 299, 691694, doi:10.1126/science.1079053.

  • Hoerling, M., J. Eischeid, J. Perlwitz, X. W. Quan, T. Zhang, and P. Pegion, 2012: On the increased frequency of Mediterranean drought. J. Climate, 25, 21462161, doi:10.1175/JCLI-D-11-00296.1.

    • Search Google Scholar
    • Export Citation
  • Hoskins, B. J., and K. I. Hodges, 2002: New perspectives on the Northern Hemisphere winter storm tracks. J. Atmos. Sci., 59, 10411061, doi:10.1175/1520-0469(2002)059<1041:NPOTNH>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Immerzeel, W. W., L. P. H. van Beek, M. Konz, A. B. Shrestha, and M. F. P. Bierkens, 2012: Hydrological response to climate change in a glacierized catchment in the Himalayas. Climatic Change, 110, 721736, doi:10.1007/s10584-011-0143-4.

    • Search Google Scholar
    • Export Citation
  • IPCC, 2007: Climate Change 2007: The Physical Science Basis. Cambridge University Press, 996 pp.

  • IPCC, 2012: Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation. Cambridge University Press, 582 pp. [Available online at https://www.ipcc.ch/pdf/special-reports/srex/SREX_Full_Report.pdf.]

  • IPCC, 2013a: Annex I: Atlas of global and regional climate projections. Climate Change 2013: The Physical Science Basis. T. F. Stocker et al., Eds., Cambridge University Press, 1311–1394.

  • IPCC, 2013b: Summary for policymakers. Climate Change 2013: The Physical Science Basis, T. F. Stocker et al., Eds., Cambridge University Press, 1–29.

    • Search Google Scholar
    • Export Citation
  • Jin, F., A. Kitoh, and P. Alpert, 2010: Water cycle changes over the Mediterranean: A comparison study of a super-high-resolution global model with CMIP3. Philos. Trans. Roy. Soc. London, 368A, 51375149, doi:10.1098/rsta.2010.0204.

    • Search Google Scholar
    • Export Citation
  • Kalnay, E., and Coauthors, 1996: The NCEP/NCAR 40-Year Reanalysis Project. Bull. Amer. Meteor. Soc., 77, 437471, doi:10.1175/1520-0477(1996)077<0437:TNYRP>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Kaniewski, D., E. Van Campo, and H. Weiss, 2012: Drought is a recurring challenge in the Middle East. Proc. Natl. Acad. Sci. USA, 109, 38623867, doi:10.1073/pnas.1116304109.

    • Search Google Scholar
    • Export Citation
  • Kariyeva, J., and W. J. D. van Leeuwen, 2012: Phenological dynamics of irrigated and natural drylands in central Asia before and after the USSR collapse. Agric. Ecosyst. Environ., 162, 7789, doi:10.1016/j.agee.2012.08.006.

    • Search Google Scholar
    • Export Citation
  • Katiraie-Boroujerdy, P. S., N. Nasrollahi, K. L. Hsu, and S. Sorooshian, 2016: Quantifying the reliability of four global datasets for drought monitoring over a semiarid region. Theor. Appl. Climatol., 123, 387398, doi:10.1007/s00704-014-1360-3.

    • Search Google Scholar
    • Export Citation
  • Kelley, C., M. Ting, R. Seager, and Y. Kushnir, 2012: The relative contributions of radiative forcing and internal climate variability to the late 20th century winter drying of the Mediterranean region. Climate Dyn., 38, 20012015, doi:10.1007/s00382-011-1221-z.

    • Search Google Scholar
    • Export Citation
  • Kelley, C., S. Mohtadi, M. Cane, R. Seager, and Y. Kushnir, 2015: Climate change in the Fertile Crescent and implications of the recent Syrian drought. Proc. Natl. Acad. Sci. USA, 112, 32413246, doi:10.1073/pnas.1421533112.

    • Search Google Scholar
    • Export Citation
  • Kim, D.-W., and H.-R. Byun, 2009: Future pattern of Asian drought under global warming scenario. Theor. Appl. Climatol., 98, 137150, doi:10.1007/s00704-008-0100-y.

    • Search Google Scholar
    • Export Citation
  • Kitoh, A., S. Yukimoto, A. Noda, and T. Motoi, 1997: Simulated changes in the Asian summer monsoon at times of increased atmospheric CO2. J. Meteor. Soc. Japan, 75, 1019–1031.

  • Kitoh, A., A. Yatagai, and P. Alpert, 2008: First super-high-resolution model projection that the ancient “Fertile Crescent” will disappear in this century. Hydrol. Res. Lett., 2, 14, doi:10.3178/hrl.2.1.

    • Search Google Scholar
    • Export Citation
  • Koster, R. D., and Coauthors, 2004: Regions of strong coupling between soil moisture and precipitation. Science, 305, 11381140, doi:10.1126/science.1100217.

    • Search Google Scholar
    • Export Citation
  • Krichak, S. O., M. Tsidulko, and P. Alpert, 2000: Monthly synoptic patterns associated with wet/dry conditions in the eastern Mediterranean. Theor. Appl. Climatol., 65, 215229, doi:10.1007/s007040070045.

    • Search Google Scholar
    • Export Citation
  • Krichak, S. O., P. Kishcha, and P. Alpert, 2002: Decadal trends of main Eurasian oscillations and the eastern Mediterranean precipitation. Theor. Appl. Climatol., 72, 209220, doi:10.1007/s007040200021.

    • Search Google Scholar
    • Export Citation
  • Krichak, S. O., J. S. Breitgand, S. Gualdi, and S. B. Feldstein, 2014: Teleconnection–extreme precipitation relationships over the Mediterranean region. Theor. Appl. Climatol., 117, 679692, doi:10.1007/s00704-013-1036-4.

    • Search Google Scholar
    • Export Citation
  • Krishnamurti, T. N., 1961: The subtropical jet stream of winter. J. Meteor., 18, 172191, doi:10.1175/1520-0469(1961)018<0172:TSJSOW>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Kutiel, H., and S. Paz, 1998: Sea level pressure departures in the Mediterranean and their relationship with monthly rainfall conditions in Israel. Theor. Appl. Climatol., 60, 93109, doi:10.1007/s007040050036.

    • Search Google Scholar
    • Export Citation
  • Kutiel, H., and Y. Benaroch, 2002: North Sea-Caspian Pattern (NCP)—An upper level atmospheric teleconnection affecting the eastern Mediterranean: Identification and definition. Theor. Appl. Climatol., 71, 1728, doi:10.1007/s704-002-8205-x.

    • Search Google Scholar
    • Export Citation
  • Kutiel, H., P. Maheras, M. Türkeş, and S. Paz, 2002: North Sea–Caspian Pattern (NCP)—An upper level atmospheric teleconnection affecting the eastern Mediterranean: Implications on the regional climate. Theor. Appl. Climatol., 72, 173192, doi:10.1007/s00704-002-0674-8.

    • Search Google Scholar
    • Export Citation
  • Lambert, S. J., J. Sheng, and J. Boyle, 2002: Winter cyclone frequencies in thirteen models participating in the Atmospheric Model Intercomparison Project (AMIP1). Climate Dyn., 19, 116, doi:10.1007/s00382-001-0206-8.

    • Search Google Scholar
    • Export Citation
  • Lautze, S., E. Stites, N. Nojumi, and F. Najimi, 2002: Qaht-e-Pool—A cash famine: Food insecurity in Afghanistan 1999–2002. Feinstein International Famine Center Rep., 61 pp.

  • Lionello, P., and F. Giorgi, 2007: Winter precipitation and cyclones in the Mediterranean region: Future climate scenarios in a regional simulation. Adv. Geosci., 12, 153158, doi:10.5194/adgeo-12-153-2007.

    • Search Google Scholar
    • Export Citation
  • Lotsch, A., M. A. Friedl, B. T. Anderson, and C. J. Tucker, 2005: Response of terrestrial ecosystems to recent Northern Hemispheric drought. Geophys. Res. Lett., 32, L06705, doi:10.1029/2004GL022043.

    • Search Google Scholar
    • Export Citation
  • Mann, M. E., 2002: Large-scale climate variability and connections with the Middle East in past centuries. Climatic Change, 55, 287314, doi:10.1023/A:1020582910569.

    • Search Google Scholar
    • Export Citation
  • Marcella, M. P., and E. A. B. Eltahir, 2008: The hydroclimatology of Kuwait: Explaining the variability of rainfall at seasonal and interannual time scales. J. Hydrometeor., 9, 10951105, doi:10.1175/2008JHM952.1.

    • Search Google Scholar
    • Export Citation
  • Marcella, M. P., and E. A. B. Eltahir, 2010: Effects of mineral aerosols on the summertime climate of southwest Asia: Incorporating subgrid variability in a dust emission scheme. J. Geophys. Res., 115, D18203, doi:10.1029/2010JD014036.

    • Search Google Scholar
    • Export Citation
  • Marcella, M. P., and E. A. B. Eltahir, 2012a: The role of lateral boundary conditions in simulations of mineral aerosols by a regional climate model of southwest Asia. Climate Dyn., 38, 109120, doi:10.1007/s00382-010-0992-y.

    • Search Google Scholar
    • Export Citation
  • Marcella, M. P., and E. A. B. Eltahir, 2012b: Modeling the summertime climate of southwest Asia: The role of land surface processes in shaping the climate of semiarid regions. J. Climate, 25, 704719, doi:10.1175/2011JCLI4080.1.

    • Search Google Scholar
    • Export Citation
  • Mariotti, A., 2007: How ENSO impacts precipitation in southwest central Asia. Geophys. Res. Lett., 34, L16706, doi:10.1029/2007GL030078.

    • Search Google Scholar
    • Export Citation
  • Mariotti, A., N. Zeng, and K. M. Lau, 2002: Euro-Mediterranean rainfall and ENSO—A seasonally varying relationship. Geophys. Res. Lett., 29, 1621, doi:10.1029/2001GL014248.

    • Search Google Scholar
    • Export Citation
  • Mariotti, A., J. Ballabrera-Poy, and N. Zeng, 2005: Tropical influence on Euro-Asian autumn rainfall variability. Climate Dyn., 24, 511521, doi:10.1007/s00382-004-0498-6.

    • Search Google Scholar
    • Export Citation
  • Mariotti, A., N. Zeng, J.-H. Yoon, V. Artale, A. Navarra, P. Alpert, and L. Z. X. Li, 2008: Mediterranean water cycle changes: Transition to drier 21st century conditions in observations and CMIP3 simulations. Environ. Res. Lett., 3, 044001, doi:10.1088/1748-9326/3/4/044001.

    • Search Google Scholar
    • Export Citation
  • Martyn, D., 1992: Climates of the World. Elsevier, 436 pp.

  • Menon, A., A. Levermann, J. Schewe, J. Lehmann, and K. Frieler, 2013: Consistent increase in Indian monsoon rainfall and its variability across CMIP-5 models. Earth Syst. Dyn., 4, 287300, doi:10.5194/esd-4-287-2013.

    • Search Google Scholar
    • Export Citation
  • Micklin, P., 1988: Desiccation of the Aral Sea: A water management disaster in the Soviet Union. Science, 241, 11701176, doi:10.1126/science.241.4870.1170.

    • Search Google Scholar
    • Export Citation
  • Micklin, P., and N. V. Aladin, 2008: Reclaiming the Aral Sea. Sci. Amer., 48, 6471, doi:10.1038/scientificamerican0408-64.

  • Miller, R. L., I. Tegen, and J. Perlwitz, 2004: Surface radiative forcing by soil dust aerosols and the hydrologic cycle. J. Geophys. Res., 109, D04203, doi:10.1029/2003JD004085.

    • Search Google Scholar
    • Export Citation
  • Mishra, A. K., and V. P. Singh, 2010: A review of drought concepts. J. Hydrol., 391, 202216, doi:10.1016/j.jhydrol.2010.07.012.

  • Morin, E., 2011: To know what we cannot know: Global mapping of minimal detectable absolute trends in annual precipitation. Water Resour. Res., 47, W07505, doi:10.1029/2010WR009798.

    • Search Google Scholar
    • Export Citation
  • Nazemosadat, M. J., and A. R. Ghasemi, 2004: Quantifying the ENSO-related shifts in the intensity and probability of drought and wet periods in Iran. J. Climate, 17, 40054018, doi:10.1175/1520-0442(2004)017<4005:QTESIT>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Nazemosadat, M. J., and H. Ghaedamini, 2010: On the relationships between the Madden–Julian oscillation and precipitation variability in southern Iran and the Arabian Peninsula: Atmospheric circulation analysis. J. Climate, 23, 887904, doi:10.1175/2009JCLI2141.1.

    • Search Google Scholar
    • Export Citation
  • Nezlin, N. P., A. G. Kostianoy, and S. A. Lebedev, 2004: Interannual variations of the discharge of Amu Darya and Syr Darya estimated from global atmospheric precipitation. J. Mar. Syst., 47, 6775, doi:10.1016/j.jmarsys.2003.12.009.

    • Search Google Scholar
    • Export Citation
  • Nezlin, N. P., A. G. Kostianoy, and B. L. Li, 2005: Inter-annual variability and interaction of remote-sensed vegetation index and atmospheric precipitation in the Aral Sea region. J. Arid Environ., 62, 677700, doi:10.1016/j.jaridenv.2005.01.015.

    • Search Google Scholar
    • Export Citation
  • Niranjan, K., and T. B. M. J. Ouarda, 2014: Precipitation variability over UAE and global SST teleconnections. J. Geophys. Res. Atmos., 119, 10 31310 322, doi:10.1002/2014JD021724.

    • Search Google Scholar
    • Export Citation
  • NOAA, 1988: Data announcement 88-MGG-02: Digital relief of the surface of the earth. NOAA National Geophysical Data Center, accessed 27 March 2003.

  • Nortcliff, S., E. Black, and R. Potter, 2011: Current water demands and future strategies under changing climatic conditions. Water, Life and Civilisation: Climate, Environment and Society in the Jordan Valley, S. Mithen, and E. Black, Eds., Cambridge University Press, 403–415.

  • Oki, T., and S. Kanae, 2006: Global hydrological cycles and world water resources. Science, 313, 10681072, doi:10.1126/science.1128845.

    • Search Google Scholar
    • Export Citation
  • Paz, S., Y. M. Tourre, and S. Planton, 2003: North Africa-west Asia (NAWA) sea-level pressure patterns and their linkages with the eastern Mediterranean (EM) climate. Geophys. Res. Lett., 30, 1999, doi:10.1029/2003GL017862.

    • Search Google Scholar
    • Export Citation
  • Pinto, J. G., U. Ulbrich, G. C. Leckebusch, T. Spangehl, M. Reyers, and S. Zacharias, 2007: Changes in storm track and cyclone activity in three SRES ensemble experiments with the ECHAM5/MPI-OM1 GCM. Climate Dyn., 29, 195210, doi:10.1007/s00382-007-0230-4.

    • Search Google Scholar
    • Export Citation
  • Pinzon, J., M. E. Brown, and C. J. Tucker, 2005: Satellite time series correction of orbital drift artifacts using empirical mode decomposition. Hilbert–Huang Transform and Its Applications, N. Huang and S. Shen, Eds., World Scientific, 167–186.

    • Search Google Scholar
    • Export Citation
  • Polade, S., D. W. Pierce, D. R. Cayan, A. Gershunov, M. D. Dettinger, 2014: The key role of dry days in changing regional climate and precipitation regimes. Sci. Rep., 4, 4364, doi:10.1038/srep04364.

    • Search Google Scholar
    • Export Citation
  • Pourasghar, F., T. Tozuka, S. Jahanbakhsh, B. Sari Sarraf, H. Ghaemi, and T. Yamagata, 2012: The interannual precipitation variability in the southern part of Iran as linked to large-scale climate modes. Climate Dyn., 39, 23292341, doi:10.1007/s00382-012-1357-5.

    • Search Google Scholar
    • Export Citation
  • Pourasghar, F., T. Tozuka, H. Ghaemi, P. Oettli, S. Jahanbakhsh, and T. Yamagata, 2015: Influences of the MJO on intraseasonal rainfall variability over southern Iran. Atmos. Sci. Lett., 16, 110118, doi:10.1002/asl2.531.

    • Search Google Scholar
    • Export Citation
  • Price, C., L. Stone, A. Huppert, B. Rajagopalan, and P. Alpert, 1998: A possible link between El Niño and precipitation in Israel. Geophys. Res. Lett., 25, 39633966, doi:10.1029/1998GL900098.

    • Search Google Scholar
    • Export Citation
  • Ramankutty, N., A. Evan, C. Monfreda, and J. A. Foley, 2008: Farming the planet: 1. Geographic distribution of global agricultural lands in the year 2000. Global Biogeochem. Cycles, 22, GB1003, doi:10.1029/2007GB002952.

    • Search Google Scholar
    • Export Citation
  • Rodwell, M. J., and B. J. Hoskins, 1996: Monsoons and the dynamics of deserts. Quart. J. Roy. Meteor. Soc., 122, 13851404, doi:10.1002/qj.49712253408.

    • Search Google Scholar
    • Export Citation
  • Rodwell, M. J., and B. J. Hoskins, 2001: Subtropical anticyclones and summer monsoons. J. Climate, 14, 31923211, doi:10.1175/1520-0442(2001)014<3192:SAASM>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Ropelewski, C. F., and M. S. Halpert, 1987: Global and regional scale precipitation patterns associated with the El Niño/Southern Oscillation. Mon. Wea. Rev., 115, 16061626, doi:10.1175/1520-0493(1987)115<1606:GARSPP>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Rudolf, B., T. Fuchs, U. Schneider, and A. Meyer-Christoffer, 2003: Introduction of the Global Precipitation Climatology Centre (GPCC). GPCC Rep., 16 pp.

  • Ryan, J., R. Sommer, and H. Ibrikci, 2012: Fertilizer best management practices: A perspective from the dryland west Asia–North Africa region. J. Agron. Crop Sci., 198, 5767, doi:10.1111/j.1439-037X.2011.00488.x.

    • Search Google Scholar
    • Export Citation
  • Saaroni, H., B. Ziv, J. Edelson, and P. Alpert, 2003: Long-term variations in summer temperatures over the eastern Mediterranean. Geophys. Res. Lett., 30, 1946, doi:10.1029/2003GL017742.

    • Search Google Scholar
    • Export Citation
  • Saaroni, H., B. Ziv, I. Osetinsky, and P. Alpert, 2010: Factors governing the interannual variation and the long-term trend of the 850 hPa temperature over Israel. Quart. J. Roy. Meteor. Soc., 136, 305318, doi:10.1002/qj.580.

    • Search Google Scholar
    • Export Citation
  • Saini, R., M. Barlow, and A. Hoell, 2011: Dynamics and thermodynamics of the regional response to the Indian monsoon onset. J. Climate, 24, 58795886, doi:10.1175/2011JCLI3928.1.

    • Search Google Scholar
    • Export Citation
  • Schär, C., L. Vasilina, F. Pertziger, and S. Dirren, 2004: Seasonal runoff forecasting using precipitation from meteorological data assimilation systems. J. Hydrometeor., 5, 959973, doi:10.1175/1525-7541(2004)005<0959:SRFUPF>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Scheffer, M., M. Holmgren, V. Brovkin, and M. Claussen, 2005: Synergy between small- and large-scale feedbacks of vegetation on the water cycle. Global Change Biol., 11, 10031012, doi:10.1111/j.1365-2486.2005.00962.x.

    • Search Google Scholar
    • Export Citation
  • Schiemann, R., M. G. Glazirina, and C. Schär, 2007: On the relationship between the Indian summer monsoon and river flow in the Aral Sea basin. Geophys. Res. Lett., 34, L05706, doi:10.1029/2006GL028926.

    • Search Google Scholar
    • Export Citation
  • Schiemann, R., D. Lüthi, P. L. Vidale, and C. Schär, 2008: The precipitation climate of central Asia—Intercomparison of observational and numerical data sources in a remote semiarid region. Int. J. Climatol., 28, 295314, doi:10.1002/joc.1532.

    • Search Google Scholar
    • Export Citation
  • Schiemann, R., D. Lüthi, and C. Schär, 2009: Seasonality and interannual variability of the westerly jet in the Tibetan Plateau region. J. Climate, 22, 29402957, doi:10.1175/2008JCLI2625.1.

    • Search Google Scholar
    • Export Citation
  • Schneider, U., A. Becker, P. Finger, A. Meyer-Christoffer, M. Ziese, and B. Rudolf, 2014: GPCC’s new land surface precipitation climatology based on quality-controlled in situ data and its role in quantifying the global water cycle. Theor. Appl. Climatol., 115, 1540, doi:10.1007/s00704-013-0860-x.

    • Search Google Scholar
    • Export Citation
  • Seager, R., N. Harnik, Y. Kushnir, W. Robinson, and J. Miller, 2003: Mechanisms of hemispherically symmetric climate variability. J. Climate, 16, 29602978, doi:10.1175/1520-0442(2003)016<2960:MOHSCV>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Seager, R., N. Harnik, W. Robinson, Y. Kushnir, M. Ting, H. Huang, and J. Velez, 2005: Mechanisms of ENSO-forcing of hemispherically symmetric precipitation variability. Quart. J. Roy. Meteor. Soc., 131, 15011527, doi:10.1256/qj.04.96.

    • Search Google Scholar
    • Export Citation
  • Seager, R., H. B. Liu, N. Henderson, I. Simpson, C. Kelley, T. Shaw, Y. Kushnir, and M. F. Ting, 2014: Causes of increasing aridification of the Mediterranean region in response to rising greenhouse gases. J. Climate, 27, 46554676, doi:10.1175/JCLI-D-13-00446.1.

    • Search Google Scholar
    • Export Citation
  • Selby, J., and C. Hoffmann, 2012: Water scarcity, conflict, and migration: A comparative analysis and reappraisal. Environ. Plann., 30C, 9971014, doi:10.1068/c11335j.

    • Search Google Scholar
    • Export Citation
  • Sheffield, J., and E. F. Wood, 2008: Global trends and variability in soil moisture and drought characteristics, 1950–2000, from observation-driven simulations of the terrestrial hydrologic cycle. J. Climate, 21, 432458, doi:10.1175/2007JCLI1822.1.

    • Search Google Scholar
    • Export Citation
  • Shohami, D., U. Dayan, and E. Morin, 2011: Warming and drying of the eastern Mediterranean: Additional evidence from trend analysis. J. Geophys. Res., 116, D22101, doi:10.1029/2011JD016004.

  • Simpson, I. R., R. Seager, T. A. Shaw, and M. Ting, 2015: Mediterranean summer climate and the importance of Middle East topography. J. Climate, 28, 19771996, doi:10.1175/JCLI-D-14-00298.1.

    • Search Google Scholar
    • Export Citation
  • Singh, P., and L. Bengtsson, 2004: Hydrological sensitivity of a large Himalayan basin to climate change. Hydrol. Processes, 18, 23632385, doi:10.1002/hyp.1468.

    • Search Google Scholar
    • Export Citation
  • Sorg, A., T. Bolch, M. Stoffel, O. Solomina, and M. Beniston, 2012: Climate change impacts on glaciers and runoff in Tien Shan (central Asia). Nat. Climate Change, 2, 725731, doi:10.1038/nclimate1592.

    • Search Google Scholar
    • Export Citation
  • Sorg, A., M. Huss, M. Rohrer, and M. Stoffel, 2014: The days of plenty might soon be over in glacierized central Asian catchments. Environ. Res. Lett., 9, 104018, doi:10.1088/1748-9326/9/10/104018.

    • Search Google Scholar
    • Export Citation
  • Stowasser, M., H. Annamalai, and J. Hafner, 2009: Response of the South Asian summer monsoon to global warming: Mean and synoptic systems. J. Climate, 22, 10141036, doi:10.1175/2008JCLI2218.1.

    • Search Google Scholar
    • Export Citation
  • Sud, Y. C., J. Shukla, and Y. Mintz, 1988: Influence of land surface roughness on atmospheric circulation and precipitation: A sensitivity study with a general circulation model. J. Appl. Meteor., 27, 10361054, doi:10.1175/1520-0450(1988)027<1036:IOLSRO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Sutton, R. T., B. Dong, and J. M. Gregory, 2007: Land/sea warming ratio in response to climate change: IPCC AR4 model results and comparison with observations. Geophys. Res. Lett., 34, L02701, doi:10.1029/2006GL028164.

    • Search Google Scholar
    • Export Citation
  • Syed, F. S., F. Giorgi, J. S. Pal, and M. P. King, 2006: Effect of remote forcings on the winter precipitation of central southwest Asia part 1: Observations. Theor. Appl. Climatol., 86, 147160, doi:10.1007/s00704-005-0217-1.

    • Search Google Scholar
    • Export Citation
  • Thenkabail, P. S., M. S. D. N. Gamage, and V. U. Smakhtin, 2004: The use of remote-sensing data for drought assessment and monitoring in Southwest Asia. International Water Management Institute (Colombo, Sri Lanka) Research Rep. 85, 25 pp.

  • Tippett, M. K., M. Barlow, and B. Lyon, 2003: Statistical correction of central southwest Asia winter precipitation simulations. Int. J. Climatol., 23, 14211433, doi:10.1002/joc.947.

    • Search Google Scholar
    • Export Citation
  • Tippett, M. K., L. Goddard, and A. G. Barnston, 2005: Statistical–dynamical seasonal forecasts of central-southwest Asian winter precipitation. J. Climate, 18, 18311843, doi:10.1175/JCLI3371.1.

    • Search Google Scholar
    • Export Citation
  • Tippett, M. K., M. Almazroui, and I.-S. Kang, 2015: Extended-range forecasts of areal-averaged Saudi Arabia rainfall. Wea. Forecasting, 30, 10901105, doi:10.1175/WAF-D-15-0011.1.

    • Search Google Scholar
    • Export Citation
  • Törnros, T., and L. Menzel, 2014: Addressing drought conditions under current and future climates in the Jordan River region. Hydrol. Earth Syst. Sci., 18, 305318, doi:10.5194/hess-18-305-2014.

    • Search Google Scholar
    • Export Citation
  • Tourre, Y., and S. Paz, 2004: The North-Africa/western Asia (NAWA) sea level pressure index: A Mediterranean signature of the northern annular mode (NAM). Geophys. Res. Lett., 31, L17209, doi:10.1029/2004GL020414.

    • Search Google Scholar
    • Export Citation
  • Trigo, I. F., T. D. Davies, and G. R. Bigg, 1999: Objective climatology of cyclones in the Mediterranean region. J. Climate, 12, 16851696, doi:10.1175/1520-0442(1999)012<1685:OCOCIT>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Trigo, R. M., C. Gouveia, and D. Barriopedro, 2010: The intense 2007–2009 drought in the Fertile Crescent: Impacts and associated atmospheric circulation. Agric. For. Meteor., 150, 12451257, doi:10.1016/j.agrformet.2010.05.006.

    • Search Google Scholar
    • Export Citation
  • Tsvieli, Y., and A. Zangvil, 2005: Synoptic climatological analysis of ‘wet’ and ‘dry’ Red Sea troughs over Israel. Int. J. Climatol., 25, 19972015, doi:10.1002/joc.1232.

    • Search Google Scholar
    • Export Citation
  • Tucker, C. J., J. E. Pinzon, M. E. Brown, D. Slayback, E. W. Pak, R. Mahoney, E. Vermote, and N. El Saleous, 2005: An extended AVHRR 8-km NDVI dataset compatible with MODIS and SPOT vegetation NDVI data. Int. J. Remote Sens., 26, 44854498, doi:10.1080/01431160500168686.

    • Search Google Scholar
    • Export Citation
  • Turner, A. G., and H. Annamalai, 2012: Climate change and the South Asian summer monsoon. Nat. Climate Change, 2, 19, doi:10.1038/nclimate1495.

    • Search Google Scholar
    • Export Citation
  • Turner, A. G., P. M. Inness, and J. M. Slingo, 2007: The effect of doubled CO2 and model basic state biases on the monsoon-ENSO system. I: Mean response and interannual variability. Quart. J. Roy. Meteor. Soc., 133, 11431157, doi:10.1002/qj.82.

    • Search Google Scholar
    • Export Citation
  • Tyrlis, E., J. Lelieveld, and B. Steil, 2013: The summer circulation over the eastern Mediterranean and the Middle East: Influence of the South Asian monsoon. Climate Dyn., 40, 11031123, doi:10.1007/s00382-012-1528-4.

    • Search Google Scholar
    • Export Citation
  • Ulbrich, U., W. May, L. Li, P. Lionello, J. G. Pinto, and S. Somot, 2006: The Mediterranean climate change under global warming. Developments in Earth and Environmental Sciences, P. Lionello et al., Eds., Elsevier, 399–415.

    • Search Google Scholar
    • Export Citation
  • Voss, K. A., J. S. Famiglietti, M.-H. Lo, C. de Linage, M. Rodell, and S. C. Swenson, 2013: Groundwater depletion in the Middle East from GRACE with implications for transboundary water management in the Tigris-Euphrates-western Iran region. Water Resour. Res., 49, doi:10.1002/wrcr.20078.

    • Search Google Scholar
    • Export Citation
  • Wade, A. J., E. C. L. Black, D. J. Brayshaw, M. El-Bastawesy, P. A. C. Holmes, D. Butterfield, S. Nuimat, and K. Jamjoum, 2010: A model-based assessment of the effects of projected climate change on the water resources of Jordan. Philos. Trans. Roy. Soc. London, 368A, 51515172, doi:10.1098/rsta.2010.0207.

    • Search Google Scholar
    • Export Citation
  • Waliser, D. E., K. M. Lau, W. Stern, and C. Jones, 2003: Potential predictability of the Madden–Julian oscillation. Bull. Amer. Meteor. Soc., 84, 3350, doi:10.1175/BAMS-84-1-33.

    • Search Google Scholar
    • Export Citation
  • Walters, K., and W. Sjoberg, 1988: The Persian Gulf region—A climatological study. USAF Tech. Note USAFETAC/TN-88/002, 62 pp.

  • Weiss, H., and R. S. Bradley, 2001: What drives societal collapse? Science, 291, 609610, doi:10.1126/science.1058775.

  • Xie, P., and P. A. Arkin, 1996: Analyses of global monthly precipitation using gauge observations, satellite estimates, and numerical model predictions. J. Climate, 9, 840858, doi:10.1175/1520-0442(1996)009<0840:AOGMPU>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Xie, P., and P. A. Arkin, 1997: Global precipitation: A 17-year monthly analysis based on gauge observations, satellite estimates, and numerical model outputs. Bull. Amer. Meteor. Soc., 78, 25392558, doi:10.1175/1520-0477(1997)078<2539:GPAYMA>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Yin, Z. Y., H. Wang, and X. Liu, 2014: A comparative study on precipitation climatology and interannual variability in the lower midlatitude East Asia and central Asia. J. Climate, 27, 78307848, doi:10.1175/JCLI-D-14-00052.1.

    • Search Google Scholar
    • Export Citation
  • Yosef, Y., H. Saaroni, and P. Alpert, 2009: Trends in daily rainfall intensity over Israel 1950/1-2003/4. Open Atmos. Sci. J., 3, 196203, doi:10.2174/1874282300903010196.

    • Search Google Scholar
    • Export Citation
  • Zaitchik, B. F., J. P. Evans, R. A. Geerken, and R. B. Smith, 2007: Climate and vegetation in the Middle East: Interannual variability and drought feedbacks. J. Climate, 20, 39243941, doi:10.1175/JCLI4223.1.

    • Search Google Scholar
    • Export Citation
  • Zeng, N., and J. Yoon, 2009: Expansion of the world’s deserts due to vegetation-albedo feedback under global warming. Geophys. Res. Lett., 36, L17401, doi:10.1029/2009GL039699.

    • Search Google Scholar
    • Export Citation
  • Zhang, X., and Coauthors, 2005: Trends in Middle East climate extreme indices from 1950 to 2003. J. Geophys. Res., 110, D22104, doi:10.1029/2005JD006181.

    • Search Google Scholar
    • Export Citation
  • Ziv, B., H. Saaroni, and P. Alpert, 2004: The factors governing the summer regime of the eastern Mediterranean. Int. J. Climatol., 24, 18591871, doi:10.1002/joc.1113.

    • Search Google Scholar
    • Export Citation
  • Ziv, B., U. Dayan, and D. Sharon, 2005a: A mid-winter, tropical extreme flood-producing storm in southern Israel: Synoptic scale analysis. Meteor. Atmos. Phys., 88, 5363, doi:10.1007/s00703-003-0054-7.

    • Search Google Scholar
    • Export Citation
  • Ziv, B., H. Saaroni, A. Baharad, D. Yekutieli, and P. Alpert, 2005b: Indications for aggravation in summer heat conditions over the Mediterranean basin. Geophys. Res. Lett., 32, L12706, doi:10.1029/2005GL022796.

    • Search Google Scholar
    • Export Citation
  • Ziv, B., U. Dayan, Y. Kushnir, C. Roth, and Y. Enzel, 2006: Regional and global atmospheric patterns governing rainfall in the southern Levant. Int. J. Climatol., 26, 5573, doi:10.1002/joc.1238.

    • Search Google Scholar
    • Export Citation
  • Ziv, B., H. Saaroni, R. Pargament, T. Harpaz, and P. Alpert, 2014: Trends in rainfall regime over Israel, 1975–2010, and their relationship to large-scale variability. Reg. Environ. Change, 14, 17511764, doi:10.1007/s10113-013-0414-x.

    • Search Google Scholar
    • Export Citation
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    The 1999–2001 drought, as measured by the 12-month standardized precipitation index (SPI), calculated based on precipitation from the CPC Merged Analysis of Precipitation (CMAP; Xie and Arkin 1996, 1997), relative to the 1979–2010 period. The red oval denotes the focus area for this review.

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    Countries considered here (in gray) along with approximate definitions of three subdomains often focused on in regional studies (Middle East, in red; Fertile Crescent, in green; and southwest Asia, in blue). Definitions of these regions vary considerably: more expansive definitions of the Middle East include the entire domain; more restrictive definitions focus on the coastal countries. The region as a whole is also sometimes referred to as western Asia.

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    (top) Population count and (bottom) poverty estimates. Estimated infant mortality rate (infant deaths per 10 000 live births) is used here as a measure of poverty. The unit of population is number of persons and the unit of infant mortality rate is infant deaths per 10 000 live births. Both the population data and the infant mortality rate are from the Center for International Earth Science Information Network (CIESIN), Columbia University (Center for International Earth Science Information Network 2005).

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    (a) Annual mean precipitation (cm), (b) elevation (km), (c) growing season vegetation, and (d) coefficient of variation for annual precipitation (ratio of the standard deviation to the mean). The contour intervals for precipitation and elevation are 10 cm and 0.5 km, respectively. The growing season vegetation is estimated by April–August normalized difference vegetation index (NDVI). Both NDVI and the coefficient of variation are unitless ratios, with contour intervals of 0.1 in both cases. The NDVI is shaded from light green (least vegetative vigor) to red (most vigor) to allow visual discrimination of the large range in vegetative vigor over the region. The GPCC version 6 dataset (Schneider et al. 2014; Rudolf et al. 2003) is used for precipitation, with the averaged calculated for the 1951–2010 period. The Global Inventory Modeling and Mapping Studies (GIMMS) NDVIg dataset (Pinzon et al. 2005; Tucker et al. 2005), produced by the Global Land Cover Facility (GLCF) at the University of Maryland, College Park, is used for NDVI for the1981–2006 period. The ETOPO5 dataset (NOAA 1988) is used for topography.

  • View in gallery

    Annual precipitation (cm) in Jerusalem for 1950/51–2012/13. The precipitation data were obtained from the Israel Meteorological Service.

  • View in gallery

    Station data availability underlying the GPCC version 6 dataset, as in Fig. 4, for the 1951–2010 period, on the 0.5°-resolution grid. The availability is given in terms of the percent of months in the 60-yr period that have at least one station report per grid box for each month. That is, a value of 100 for an individual grid box indicates that for each month in the period, there was at least one station report within the area of the grid box, whereas a value of 0 indicates that all the monthly values in the period for that grid box were based on interpolation.

  • View in gallery

    Seasonal cycle of precipitation, in terms of (left) total values and (right) percent of annual mean. The total values are shown in intervals of 10 cm, with an additional first interval of 2 cm. The percent of annual mean is shown in intervals of 5% and brown shading for values <25% (the point at which all seasons would be contributing equally) and in intervals of 10% and green shading for values >25%. Calculations are based on CMAP (Xie and Arkin 1996, 1997) for the 1979–2010 period. The CMAP dataset is used here to allow inclusion of ocean precipitation.

  • View in gallery

    (left) January and (right) July circulation fields: (a),(b) 300-hPa wind (vectors and speed colored shading); (c),(d) SLP; and (e),(f) 200-hPa synoptic transients. A 2–8-day-filtered 200-hPa meridional wind variance is used as the estimate of upper-level synoptic transients. The contour interval for wind speed is 10 m s−1, SLP is 4 hPa, and synoptic transients is 10 m2 s−2. The calculations are based on the NCEP–NCAR reanalysis (Kalnay et al. 1996) for the 1951–2010 period.

  • View in gallery

    Schematic of drought mechanisms for the 1999–2001 and 2007/08 severe regional droughts.

  • View in gallery

    Number of countries in the region (of 19 total) experiencing annual precipitation deficits during the 1951–2010 period. The three brown shades (light, medium, and dark) indicate the number of countries with annual precipitation below, 90%, and 75% of average. The calculations are based on GPCC version 6 data on the 0.5° grid, averaged over the land area of each country. The open circles indicate years where at least 16 of the 19 countries had less-than-average precipitation.

  • View in gallery

    Composite of SST anomalies (°C) for the 11 yr in the 1951–2010 period when at least 16 of the 19 countries in the region reported annual precipitation less than average (the open circles in Fig. 10), based on the GPCC version 6 precipitation data. The shading interval is 0.1°C and gray stippling is shown over regions not significant at the 5% level.

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A Review of Drought in the Middle East and Southwest Asia

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  • 1 * Department of Environmental, Earth, and Atmospheric Sciences, University of Massachusetts Lowell, Lowell, Massachusetts
  • | 2 Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Maryland
  • | 3 Department of Geography, University of Haifa, Haifa, Israel
  • | 4 Department of Meteorology, University of Reading, Reading, United Kingdom
  • | 5 Climate Change Research Centre, University of New South Wales, Kensington, Australia
  • | 6 ** Department of Geography, University of California, Santa Barbara, Santa Barbara, California
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Abstract

The Middle East and southwest Asia are a region that is water stressed, societally vulnerable, and prone to severe droughts. Large-scale climate variability, particularly La Niña, appears to play an important role in regionwide droughts, including the two most severe of the last 50 years—1999–2001 and 2007/08—with implications for drought forecasting. Important dynamical factors include orography, thermodynamic influence on vertical motion, storm-track changes, and moisture transport. Vegetation in the region is strongly impacted by drought and may provide an important feedback mechanism. In future projections, drying of the eastern Mediterranean region is a robust feature, as are temperature increases throughout the region, which will affect evaporation and the timing and intensity of snowmelt. Vegetation feedbacks may become more important in a warming climate. There are a wide range of outstanding issues for understanding, monitoring, and predicting drought in the region, including dynamics of the regional storm track, the relative importance of the range of dynamical mechanisms related to drought, the regional coherence of drought, the relationship between synoptic-scale mechanisms and drought, the predictability of vegetation and crop yields, the stability of remote influences, data uncertainty, and the role of temperature. Development of a regional framework for cooperative work and dissemination of information and existing forecasts would speed understanding and make better use of available information.

Corresponding author address: Mathew Barlow, Department of Environmental, Earth, and Atmospheric Sciences, 1 University Ave., University of Massachusetts Lowell, Lowell, MA 01854. E-mail: mathew_barlow@uml.edu

This article is included in the GDIS Drought Worldwide Special Collection.

Abstract

The Middle East and southwest Asia are a region that is water stressed, societally vulnerable, and prone to severe droughts. Large-scale climate variability, particularly La Niña, appears to play an important role in regionwide droughts, including the two most severe of the last 50 years—1999–2001 and 2007/08—with implications for drought forecasting. Important dynamical factors include orography, thermodynamic influence on vertical motion, storm-track changes, and moisture transport. Vegetation in the region is strongly impacted by drought and may provide an important feedback mechanism. In future projections, drying of the eastern Mediterranean region is a robust feature, as are temperature increases throughout the region, which will affect evaporation and the timing and intensity of snowmelt. Vegetation feedbacks may become more important in a warming climate. There are a wide range of outstanding issues for understanding, monitoring, and predicting drought in the region, including dynamics of the regional storm track, the relative importance of the range of dynamical mechanisms related to drought, the regional coherence of drought, the relationship between synoptic-scale mechanisms and drought, the predictability of vegetation and crop yields, the stability of remote influences, data uncertainty, and the role of temperature. Development of a regional framework for cooperative work and dissemination of information and existing forecasts would speed understanding and make better use of available information.

Corresponding author address: Mathew Barlow, Department of Environmental, Earth, and Atmospheric Sciences, 1 University Ave., University of Massachusetts Lowell, Lowell, MA 01854. E-mail: mathew_barlow@uml.edu

This article is included in the GDIS Drought Worldwide Special Collection.

1. Introduction

The Middle East and southwest Asia are a highly water-stressed region with reduced societal resilience resulting from economic and political challenges. As a result, severe drought in the region can have complex impacts, ranging beyond direct impacts on crops and livestock to an array of indirect impacts associated with sanitation, nutrition, loss of livelihood, displaced populations, and international disputes. As an example, the catastrophic 1999–2001 drought resulted in impacts spanning crop failures; widespread livestock death; significant population migrations; increases in diseases (polio, cholera, diphtheria, typhoid, and tuberculosis); soil and land cover degradation; loss of orchards and fruit trees both as a result of direct drought impacts and through use as fuel; desiccation of internationally important wetlands; increase in household debt, with a disproportionate impact on women and children; and international boundary disputes over both river flows and refugees (Agrawala et al. 2001; Lautze et al. 2002). In terms of standardized precipitation deficits, this regional drought comprised the most severe area of drought in the world during this period (Fig. 1). (Datasets are described in figure captions.) Moreover, future drought impacts may be even worse, as consensus model projections suggest an overall drying trend for much of the region (IPCC 2013a). Understanding the dynamics, predictability, and trends of droughts in this region is, therefore, a critically important problem. This review assesses the current understanding of drought in this sensitive region with regard to both the historical record and future projections and identifies outstanding questions. In addition to drought research, previous results with respect to the region’s climatology, hydrology, vegetation, and precipitation processes that are not focused specifically on drought but are relevant to understanding drought are also surveyed.

Fig. 1.
Fig. 1.

The 1999–2001 drought, as measured by the 12-month standardized precipitation index (SPI), calculated based on precipitation from the CPC Merged Analysis of Precipitation (CMAP; Xie and Arkin 1996, 1997), relative to the 1979–2010 period. The red oval denotes the focus area for this review.

Citation: Journal of Climate 29, 23; 10.1175/JCLI-D-13-00692.1

The terms “Middle East” and “southwest Asia” both have varying definitions. For the purposes of this study, the region considered extends from the east coast of the Mediterranean Sea through Pakistan, along with the Arabian Peninsula, and includes the following countries (Fig. 2): Israel, Lebanon, Syria, Jordan, Saudi Arabia, Oman, Qatar, the United Arab Emirates, Kuwait, Bahrain, Yemen, Iraq, Iran, Afghanistan, Tajikistan, Uzbekistan, Kyrgyzstan, Turkmenistan, and Pakistan. This area is chosen to be relatively broad while considering an area of generally similar climate (although ranging from Mediterranean climate to semiarid and arid conditions) that is influenced by regionwide drought mechanisms. The region includes an arc of relatively fertile land, the Fertile Crescent, which is indicated schematically on Fig. 2 along with the definitions of Middle East and southwest Asia used in this review.

Fig. 2.
Fig. 2.

Countries considered here (in gray) along with approximate definitions of three subdomains often focused on in regional studies (Middle East, in red; Fertile Crescent, in green; and southwest Asia, in blue). Definitions of these regions vary considerably: more expansive definitions of the Middle East include the entire domain; more restrictive definitions focus on the coastal countries. The region as a whole is also sometimes referred to as western Asia.

Citation: Journal of Climate 29, 23; 10.1175/JCLI-D-13-00692.1

As discussed further in the next section, the climate of the region is generally semiarid to very arid, including several deserts, but annual precipitation does exceed 60 cm along the eastern Mediterranean region and on many of the mountain slopes in the region and ranges as high as 180 cm in a small region on the southern coast of the Caspian Sea. Over much of the region, precipitation primarily comes during the cold season (November–April) from synoptic storms, although there are exceptions, including the importance of the summer monsoon in Pakistan and southeastern Afghanistan and the extension of the African summer monsoon/intertropical convergence zone (ITCZ) into the southern coast of the Arabian Peninsula. Because of its common importance for most of the region, drought variability associated with cold season precipitation processes is a particular focus of this review.

Large-scale and subsistence farming as well as pasturing are common throughout the region (e.g., Ryan et al. 2012; Ramankutty et al. 2008), so the region’s precipitation, though modest in many areas, is very important. The combined effects of water scarcity (Oki and Kanae 2006) and frequent drought over the Middle East and central-southwest Asia (Mishra and Singh 2010) affect crop yields and the regional economy (Kaniewski et al. 2012), which increases the potential for the loss of life and property (Agrawala et al. 2001).

Despite the aridity of the region, it is generally well populated outside of the highest mountains and desert regions, with an estimated population density (Fig. 3, top) similar to the southeast United States or South Africa. Within the region, there are areas of high poverty and societal vulnerability; one measure of poverty, infant mortality, is shown in Fig. 3, bottom. This vulnerability is particularly evident during severe droughts, as noted above. Moreover, given the long-standing sociopolitical tensions in several areas of the region in an environment of limited resources, drought variability may raise the risk of regional conflicts (El Kharraz et al. 2012; Selby and Hoffmann 2012; Fröhlich 2013; Gleick 2014; Kelley et al. 2015). In terms of the impacts of drought, therefore, the region is particularly important because of the intersection of population, vulnerability, drought severity, and potential aridification under climate change.

Fig. 3.
Fig. 3.

(top) Population count and (bottom) poverty estimates. Estimated infant mortality rate (infant deaths per 10 000 live births) is used here as a measure of poverty. The unit of population is number of persons and the unit of infant mortality rate is infant deaths per 10 000 live births. Both the population data and the infant mortality rate are from the Center for International Earth Science Information Network (CIESIN), Columbia University (Center for International Earth Science Information Network 2005).

Citation: Journal of Climate 29, 23; 10.1175/JCLI-D-13-00692.1

Here we review the current state of understanding of drought in the region, considering regional climate in section 2, historical drought episodes in section 3, drought dynamics in section 4, predictability in section 5, and trends and projections in section 6. The review concludes with a summary, including critical research questions for future studies of drought in the region.

2. Regional climate

To provide context for the consideration of drought dynamics, an overview of the regional climate is given. The spatial distribution and seasonality of precipitation, vegetation, and hydrology are reviewed, as well as the primary atmospheric circulation and precipitation mechanisms that constitute the processes through which drought can be expressed.

a. Distribution and seasonality of precipitation, hydrology, and vegetation

The annual mean precipitation is shown in Fig. 4a. The largest amounts occur in five main areas: the coastal eastern Mediterranean Sea, the western slopes of the Zagros Mountains in Iran and Iraq, the south coast of the Caspian Sea, the slopes of the mountain complex on the western edge of the Tibetan Plateau (the Hindu Kush, the Pamir, and the Tian Shan ranges), and the southern tip of the Arabian Peninsula. There is also significant precipitation in the Fertile Crescent, which arcs from the coastal Mediterranean Sea across southeastern Turkey, northern Syria and Iraq, and into northeastern Iran along the western Zagros (Fig. 2). The spatial distribution of precipitation is closely linked to the very significant topography of the region (Fig. 4b), especially the western slopes of the mountains, as much of the regional precipitation occurs during the cold season as a result of orographic capture from eastward-moving storm systems (Martyn 1992) guided by the upper-tropospheric westerlies (Krishnamurti 1961; Schiemann et al. 2009). The distribution of precipitation is a strong control on regional vegetation (Fig. 4c), which has implications for drought feedbacks, as discussed in section 4e. The region also includes areas of little to no precipitation, including several major deserts (nomenclature varies): the Negev in southern Israel; the Syrian Desert, inland from the coastal Mediterranean Sea; the Arabian Desert, over much of the Arabian Peninsula; the Iranian salt deserts in interior and eastern Iran; the Thar Desert in northwestern India and parts of eastern Pakistan; the Registan Desert centered on southwestern Afghanistan; and the Kara-Kum, centered in Turkmenistan.

Fig. 4.
Fig. 4.

(a) Annual mean precipitation (cm), (b) elevation (km), (c) growing season vegetation, and (d) coefficient of variation for annual precipitation (ratio of the standard deviation to the mean). The contour intervals for precipitation and elevation are 10 cm and 0.5 km, respectively. The growing season vegetation is estimated by April–August normalized difference vegetation index (NDVI). Both NDVI and the coefficient of variation are unitless ratios, with contour intervals of 0.1 in both cases. The NDVI is shaded from light green (least vegetative vigor) to red (most vigor) to allow visual discrimination of the large range in vegetative vigor over the region. The GPCC version 6 dataset (Schneider et al. 2014; Rudolf et al. 2003) is used for precipitation, with the averaged calculated for the 1951–2010 period. The Global Inventory Modeling and Mapping Studies (GIMMS) NDVIg dataset (Pinzon et al. 2005; Tucker et al. 2005), produced by the Global Land Cover Facility (GLCF) at the University of Maryland, College Park, is used for NDVI for the1981–2006 period. The ETOPO5 dataset (NOAA 1988) is used for topography.

Citation: Journal of Climate 29, 23; 10.1175/JCLI-D-13-00692.1

Throughout the Middle East and southwest Asia, interannual variability in rainfall is high. The ratio of the standard deviation to the mean (the coefficient of variation) for annual precipitation is shown in Fig. 4d, with most of the region having values larger than 20% (and often much larger). Most of the highest values are in regions with little to no precipitation or at the margins of those regions (cf. Fig. 4a). As an example of variability, the annual precipitation for Jerusalem is shown in Fig. 5 for 1950–2012; the standard deviation is 31% of the mean, and the annual values span more than a fivefold range in that period, from a minimum of 21 cm to a maximum of 113 cm.

Fig. 5.
Fig. 5.

Annual precipitation (cm) in Jerusalem for 1950/51–2012/13. The precipitation data were obtained from the Israel Meteorological Service.

Citation: Journal of Climate 29, 23; 10.1175/JCLI-D-13-00692.1

Analysis of precipitation is limited by sparse observations and the presence of steep precipitation gradients associated with the extreme terrain. Figure 6 shows the amount of monthly station observations that underlie the gridded data in the GPCC dataset for the 1951–2010 period, as used in Fig. 4 and Table 1. In addition to the poor spatial coverage in many parts of the domain, there is considerable temporal variability in coverage as well (Hoell et al. 2015). A comprehensive analysis of available precipitation data for the entire region has not yet been done, but the northern part of the domain was considered in Schiemann et al. (2008), Kuwait was considered in Marcella and Eltahir (2008), Saudi Arabia in Almazroui (2011), and Iran in Katiraie-Boroujerdy et al. (2016) for a range of different datasets and sources. In general, data agreement among observed gridded datasets is good enough for qualitative identification of wet and dry years but has a large range of uncertainty for quantitative analysis; model products and satellite estimates can provide value, especially in real-time monitoring, but have even more uncertainty. The high values of precipitation along the southern shore of the Caspian Sea are poorly represented in some observed gridded data as well as in model and satellite estimates. Despite the uncertainties, the large-scale variability appears to be well captured by the available data in the high mountains, where the precipitation is mainly from synoptic-scale systems that are well observed upstream and with precipitation strongly constrained by the orography. That is, while the spatial details of the pattern may not be well resolved, the basin-averaged amounts appear to be adequately represented (Schär et al. 2004; Barlow and Tippett 2008).

Fig. 6.
Fig. 6.

Station data availability underlying the GPCC version 6 dataset, as in Fig. 4, for the 1951–2010 period, on the 0.5°-resolution grid. The availability is given in terms of the percent of months in the 60-yr period that have at least one station report per grid box for each month. That is, a value of 100 for an individual grid box indicates that for each month in the period, there was at least one station report within the area of the grid box, whereas a value of 0 indicates that all the monthly values in the period for that grid box were based on interpolation.

Citation: Journal of Climate 29, 23; 10.1175/JCLI-D-13-00692.1

Table 1.

Cross correlation of country-averaged annual precipitation for 1951–2010. Correlations ≥0.5 shown in bold and results are rounded to one decimal for clarity. Precipitation is from the GPCC dataset, as in Fig. 4.

Table 1.

The seasonal cycle of precipitation is shown in Fig. 7, in terms of both seasonal amount (left panels) and percentage of annual mean (right panels; brown shading indicates seasonal values less than one-quarter of the annual mean, and green shading indicates values more than one-quarter of the annual mean). There are three main precipitation mechanisms in the region: cold season synoptic precipitation, which is important for much of the region; summer monsoon precipitation, which is important for Pakistan and southeastern Afghanistan; and warm season African monsoon–ITCZ precipitation extending into the southern tip of the Arabian Peninsula from Africa.

Fig. 7.
Fig. 7.

Seasonal cycle of precipitation, in terms of (left) total values and (right) percent of annual mean. The total values are shown in intervals of 10 cm, with an additional first interval of 2 cm. The percent of annual mean is shown in intervals of 5% and brown shading for values <25% (the point at which all seasons would be contributing equally) and in intervals of 10% and green shading for values >25%. Calculations are based on CMAP (Xie and Arkin 1996, 1997) for the 1979–2010 period. The CMAP dataset is used here to allow inclusion of ocean precipitation.

Citation: Journal of Climate 29, 23; 10.1175/JCLI-D-13-00692.1

Terrestrial hydrological dynamics in the region are extremely diverse and cannot be addressed comprehensively in this review. In general, the prevailing hydrology follows precipitation gradients, with major rivers originating in relatively moist highland zones and often flowing into semiarid or arid regions. In the high mountains of the region, precipitation occurs primarily during the cold season, as snow. As there is little precipitation during the warm season, the spring melt is a primary driver of peak river flows (Schär et al. 2004; Barlow and Tippett 2008). The headwaters of the Tigris and Euphrates Rivers are in the Anatolia Plateau of Turkey and the Zagros Plateau of Iran. These mountain ranges have been found to play a key role in the production of precipitation in the Fertile Crescent region (Evans et al. 2004; Alijani 2008) and, by extension, water resources in the region. Note that the headwaters are partially out of the domain considered here so that a full consideration of hydrological drought for the Fertile Crescent requires consideration of the remote precipitation in Turkey. The waters of the Tigris and Euphrates support extensive irrigation developments in all riparian states and feed the marshlands of southern Iraq, both of which have been found to affect the local climate through their influence on evaporation (Evans and Zaitchik 2008; Marcella and Eltahir 2012b). There has not been much study of soil moisture in the region, but winter and spring precipitation and temperature have a strong influence on soil moisture in the Euphrates plain (Zaitchik et al. 2007) and likely many other parts of the region as well.

Notably, the region includes several major transboundary rivers, including the Indus, the Jordan, the Tigris and Euphrates, and the Amu Dar’ya and Syr Dar’ya, all of which are subject to intense water demands, resulting in considerable political tension. On the northern border of the region, the Aral Sea, fed by the Amu Dar’ya and Syr Dar’ya, was originally the fourth largest lake in the world but was reduced to 10% of its original size by 2007 as a result of the introduction of intensive agricultural practices (Micklin 1988; Micklin and Aladin 2008).

The geographic distribution, seasonality, and interannual variability of precipitation have a clear signal in vegetation cover and variability across the region. The growing season vegetation, as broadly represented by the April–August normalized difference vegetation index (NDVI), is shown in Fig. 4c. The largest values of April–August NDVI are in a narrow band along the southern shore of the Caspian Sea in association with the largest values of precipitation in that region, as well as in the valleys of the Pamir and Tian Shan Mountains. In addition to the local correspondence with precipitation, there are notable anthropogenic fingerprints in the distribution of vegetation. This is true in large rivers with significant vegetation that has an irrigated or nonlocal relationship with precipitation, including the valleys of the Indus, Amu Dar’ya, Syr Dar’ya, Tigris, and Euphrates. Note that, although NDVI is an estimate of vegetative vigor, it does not necessarily reflect the most societally important areas of vegetation, given the widespread subsistence agriculture and livestock grazing through the region that occur in only moderately vegetated areas. Agriculture is sufficiently intensive in the former Soviet Union countries that changes in vegetation associated with the dissolution of the Soviet Union are evident (Kariyeva and van Leeuwen 2012).

b. Circulation and precipitation mechanisms

The upper-level winds, sea level pressure (SLP), and synoptic variability are shown in Fig. 8 for average January conditions (Figs. 8a,c,e) and July conditions (Figs. 8b,d,f). The synoptic variability is shown in terms of 2–8-day-filtered upper-level meridional wind variance, which is a good indicator of upper-level synoptic transient activity in the region, as discussed further below.

Fig. 8.
Fig. 8.

(left) January and (right) July circulation fields: (a),(b) 300-hPa wind (vectors and speed colored shading); (c),(d) SLP; and (e),(f) 200-hPa synoptic transients. A 2–8-day-filtered 200-hPa meridional wind variance is used as the estimate of upper-level synoptic transients. The contour interval for wind speed is 10 m s−1, SLP is 4 hPa, and synoptic transients is 10 m2 s−2. The calculations are based on the NCEP–NCAR reanalysis (Kalnay et al. 1996) for the 1951–2010 period.

Citation: Journal of Climate 29, 23; 10.1175/JCLI-D-13-00692.1

At the largest scales, the circulation changes from a cold season regime under the influence of the westerlies and associated synoptic activity to a warm season regime under the influence of the Indian monsoon. The strong westerly jet and associated synoptic activity during the cold season are seen in Figs. 8a and 8e, respectively, and the extension of the northwestern-most branch of the monsoon into northern Pakistan and southeastern Afghanistan is seen in the July–September panels of Fig. 7.

Cold season synoptic precipitation is important over much of the region and has been studied by several authors. Reconciling these previous synoptic analyses of extratropical cyclones and cyclone tracks into an overall picture is challenging, however, because of differences in spatial domain, methodology, and terminology. The transient analysis of Hoskins and Hodges (2002) provides a large-scale, general view. Over the region, they identified a prominent maximum of vertical velocity variance at midlevels and a local branch of transient activity in both meridional wind and potential temperature of the 2-PVU (1 PVU = 10−6 m−2 s−1 K kg−1) surface at upper levels, similar to the branch of transient activity shown in Fig. 8e. Their dynamically oriented analysis found that the principal track at upper levels is from the Atlantic and the principal track at lower levels is from the Mediterranean Sea—these results provide a reasonable regional-scale perspective.

More local analyses have shown considerable detail in the structures of these general paths. The cyclone tracks affecting the Fertile Crescent can be grouped into two main routes: south of Turkey toward the Caspian Sea and near Jordan or Syria toward the Persian Gulf (Trigo et al. 1999). Systems are relatively frequent but precipitation occurs only with strong surface frontal activity associated with the strongest systems (Trigo et al. 1999). For the Middle East, Cyprus lows are more important for precipitation than are Black Sea or Atlas lows. Troughs traveling along the subtropical jet stream can also generate isolated thunderstorms without strong surface fronts via inducing onshore flows from the Persian Gulf (Trigo et al. 2010). A local maximum of cyclogenesis associated with the relatively warm surface of the Caspian Sea and with Caucasus lee waves modulates the pressure field over the southern part of western Asia (Lambert et al. 2002; Paz et al. 2003). Occasionally, Red Sea troughs propagate from the south, and when they coincide with extratropical cyclones entering from the west, there can be devastating floods. This happened, for example, in November 1994 (Krichak et al. 2000; Ziv et al. 2005a). At the margins of the rainy season, Red Sea troughs play a greater role, with most rainy events resulting from a northward extension of this low (Tsvieli and Zangvil 2005). Both the eastern Mediterranean upper trough and the Red Sea trough are important along the southeastern coast of the Arabian Peninsula (Charabi and Al-Hatrushi 2010). Tropical cyclones are also an infrequent source of precipitation in that region (Al-Rawas and Valeo 2009).

The synoptic tracks affecting the southwest Asia part of the domain have not been studied as much as the Middle East part of the domain. Barlow et al. (2006) showed, for heavy precipitation events in Afghanistan, a westerly track into southwest Asia consistent with the branch of transient activity shown in Fig. 8e, as did Cannon et al. (2016) for precipitation in the western Himalayas and Karakoram.

In the summer, the Indian monsoon, in addition to directly affecting northern and southeastern Pakistan, appears to also remotely influence precipitation over the northern part of the domain via an influence on temperature and stability (Schiemann et al. 2007). It has also been suggested that the Indian monsoon may remotely force subsidence over the region (Rodwell and Hoskins 1996, 2001), with orographic interaction playing an important role (Rodwell and Hoskins 2001; Tyrlis et al. 2013; Simpson et al. 2015), and observational data supports this relationship during the monsoon onset (Saini et al. 2011) and peak phase (Ziv et al. 2004). However, this influence occurs after most of the seasonal decline in precipitation has already occurred for much of the region. The degree to which the end of the wet season is due to an increase in inhibiting factors, such as the remote forcing of the monsoon or its tropical precursors, versus a decrease in precipitation-generating factors, such as the northward retreat and weakening of the storm track, is not yet clear.

While orography plays a primary role in generating precipitation via upslope lifting, it can play that role only if sufficient water vapor is transported into the area. The water vapor transport pathways were investigated explicitly in Evans and Smith (2006) for the Fertile Crescent. They showed that most precipitation events in that area are dominated by water vapor coming from the west over the Mediterranean Sea. However, the largest precipitation events were dominated by water vapor coming from the south where the Red Sea and Persian Gulf play a role as source regions. These southerly dominated events are able to transport large amounts of water vapor into the Fertile Crescent through the formation of a mountain barrier jet west of the Zagros Mountains (Evans and Alsamawi 2011). This mountain barrier jet occurs over a relatively small spatial scale such that current global climate models (GCMs) are unlikely to represent the phenomena and hence are probably unable to produce an important class of precipitation event for the Fertile Crescent. Given the extreme terrain throughout most of the region and the scarcity of observations, it is not clear that current gridded global analyses adequately represent regional moisture fluxes.

The seasons in the Persian Gulf area of the region are sometimes divided into the northeast monsoon (December–March), the spring transition (April–May), the southwest monsoon (June–September), and the fall transition (October–November; Walters and Sjoberg 1988), as this area transitions from low-level northeasterly flow in the cold season to low-level southwesterly flow in the warm season. For the full study region, at low levels the northeastern extent is at the margin of the Siberian high during winter and the southern extent is under the influence of a shallow low pressure area over Saudi Arabia and southern Pakistan, typically identified as a thermal low. Over Saudi Arabia, field work shows that within the low pressure area there is subsidence to within 1 km of the surface and then ascent below that (Blake et al. 1983). However, the interaction of orography with remote dynamic forcing may contribute more to the center of the low pressure system over southern Pakistan and northwestern India than does direct sensible heating from the surface (Bollasina and Nigam 2011).

During summer, a low-level jet forms over the Persian Gulf, with orography, mountain slope, and land–sea breeze playing a role in the formation and strength of the jet (Giannakopoulou and Toumi 2012).

3. Historical droughts

This section reviews historical droughts as identified in the previous literature and in a drought disaster database.

In the 1940s–present period, the two most severe droughts for the region as a whole appear to be the 1999–2001 (Agrawala et al. 2001; Barlow et al. 2002; Lotsch et al. 2005; Trigo et al. 2010; Kaniewksi et al. 2012; Hoell et al. 2012) and 2007/08 droughts (Trigo et al. 2010; Kaniewski et al. 2012; Hoell et al. 2012). (The 1999–2001 period given for the first drought indicates the period of broadest impact, but the drought extended from 1998 to 2002 for some areas of the region.) Information about more local droughts as well as droughts prior to the 1940s is sparse and difficult to compare based on different definitions and data periods. As summarized in Bruins (1999), the largest precipitation deficits in Jerusalem for the 1846–1993 period are 1932/33, 1950/51, and 1959/60, all of which were less than 50% of average. For Israel as a whole, based on a hydrologic measure for the 1937–84 period, 1950/51, 1958/59, 1972/73, and 1978/79 were strong drought years. More recently, the period 2004/05–2008/09 was also very dry. The driest years for the Jordan valley identified in Black (2012) for the 1950–99 period are 1960, 1963, 1966, 1970, 1973, 1979, 1986, 1987, and 1999. Section 4d provides some new analysis of regional droughts for the 1951–2010 period in the context of regional coherence.

For an impacts-oriented perspective on historical droughts in the region, drought disasters from the Emergency Events Database (EM-DAT), the Office of U.S. Foreign Disaster Assistance/Centre for Research on the Epidemiology of Disasters (OFDA/CRED) international disaster database (Centre for Research on the Epidemiology of Disasters 2014), are shown in Table 2. A disaster is defined in this database as meeting one of the following criteria: 10 or more people reported killed, 100 or more people reported affected, declaration of a state of emergency, or a call for international assistance. While there may be some reporting issues with this database, the occurrence of a drought disaster generally tracks precipitation anomalies for Asia (Barlow et al. 2006), so it appears to be reasonable. Based on the drought disaster data, the 1999–2001 and 2007/08 droughts are the most represented, sometimes extended to 1999–2002 and 2007–10, along with more local droughts: 1969, 1971–73, and 2006 for Afghanistan; 1969–71 for Iraq; 1964 for Iran; and 1969–71, 1975, and 1977 for Yemen. Given that Yemen has a different primary precipitation mechanism (African monsoon/summer ITCZ) from the rest of the region, it may be expected to have different drought events. Because of the geography and precipitation mechanism, it seems likely that these droughts may be synchronized with drought events in the greater Horn of Africa, but this has not been studied explicitly.

Table 2.

Drought disasters as listed in the EM-DAT disaster database (Centre for Research on the Epidemiology of Disasters 2014).

Table 2.

The historical droughts listed in this section were identified based on different metrics, periods, and areas within the region. A comprehensive ranking of historical drought episodes in the region, accounting for data issues, and especially with respect to the pre-1969 record, is not possible based on the previous literature but would be very useful for assessing the dynamical influences on the region, within-region relationships, and associated predictability.

4. Drought dynamics

This section reviews results related to the dynamics of drought in the region, in terms of large-scale teleconnection patterns, synoptic regimes and climatological features, mechanisms of tropical forcing, regional coherence, vegetation, and dust.

a. Large-scale teleconnection patterns

Several large-scale teleconnection patterns have been shown to have an influence on precipitation in different areas of the region:

The strengths of these teleconnections vary considerably within the region. There are also indications of variations in the temporal stability of these relationships (Ropelewski and Halpert 1987; Price et al. 1998; Marcella and Eltahir 2008; Krichak et al. 2014)—although there are perhaps some indications that using a definition based on sea surface temperatures (SSTs) of NAO-like variability gives a stronger, more stable result than a more traditional atmospheric-based definition. ENSO has also been linked to variations in river flow (Barlow and Tippett 2008), soil moisture (Sheffield and Wood 2008), and NDVI (Kariyeva and van Leeuwen 2012) in the region.

For ENSO, it appears that the state of the western Pacific may be an important additional factor (Barlow et al. 2002; Hoerling and Kumar 2003; Hoell and Funk 2013). As noted previously, two of the most severe widespread droughts for the region were during 1999–2001 and 2007/08, both of which were associated with La Niña conditions, a warm western Pacific, and similar hemispheric wind patterns (Agrawala et al. 2001; Barlow et al. 2002; Trigo et al. 2010; Hoell et al. 2012; Hoell et al. 2014a).

For many of these teleconnection studies, the influence on precipitation has been evaluated only for subareas of the full region considered in this review. Moreover, aside from the influence of the tropical Pacific in the 1999–2001 and 2007/08 drought events, the role of these teleconnections in individual drought episodes has not been closely analyzed.

b. Synoptic regimes and climatological features

In an analysis of wet and dry years for the Jordan valley, Black (2012) found that the synoptic regimes noted previously in section 2 were also important in interannual variability and were modulated by the NAO. A wet-minus-dry composite showed that precipitation departures over the Jordan valley were out of phase with precipitation departures over southern Europe and associated with changes in storm-track structure over the Mediterranean Sea.

A major part of eastern Mediterranean precipitation is controlled by a large-scale process associated with two main anticyclonic centers: the Azorian and Siberian highs. During periods with intensive anticyclones over central Europe, the area gets drier (Kutiel and Paz 1998; Krichak et al. 2000). During these dry spells, positive SLP and midlevel height (H-500) anomaly patterns prevail over eastern Europe while negative SLP and H-500 anomalies are found over southwestern and western Europe. A more intensive anticyclonic system over central Europe during dry eastern Mediterranean seasons suggests an intensification of the westward advection of dry Asian air masses into the area (Krichak et al. 2000).

c. Mechanisms of tropical forcing

While there is not yet a complete understanding of the dynamical pathways by which tropical variability can influence the region, there have been several studies of the influence of tropical convection occurring over a region extending from the eastern Indian Ocean to the western Pacific Ocean. Enhanced tropical Indo–west Pacific Ocean convection results in diabatic heating increases, which excites baroclinic (Barlow et al. 2002, 2005, 2007; Barlow 2011; Hoell et al. 2012, 2013) and barotropic (Hoell et al. 2013) stationary Rossby waves over central-southwest Asia and the Middle East. The mean wind appears to be important in increasing the northward extent of the classic Gill–Matsuno response to tropical forcing, which assumes a resting basic state (Barlow 2011; Adames and Wallace 2014). The stationary Rossby waves thermodynamically interact with the mean climate, resulting in modifications to the mid- and upper-tropospheric temperature advection, which is balanced by precipitation-suppressing subsidence (Barlow et al. 2005; Hoell et al. 2012; Hoell et al. 2014b). Anticyclonic circulation associated with Rossby waves also reduces the flux of moisture into the region from tropical Africa and the Arabian Peninsula (Mariotti et al. 2002, 2005; Mariotti 2007; Barlow and Tippett 2008; Hoell et al. 2014b). The Indo–west Pacific convection also appears to excite eastward-traveling barotropic Rossby waves that can travel across the Northern Hemisphere and influence the Middle East and central-southwest Asia from the west (Hoell et al. 2013). Additionally, a hemispherically symmetric influence from ENSO has been proposed in Seager et al. (2003, 2005), resulting from interaction between the tropically forced subtropical jet anomalies and transient activity.

Thus, there are indications that tropical Indo-Pacific Ocean anomalies can influence the region with a modified Gill–Matsuno-like response to the west, a response to the east that propagates around the hemisphere, and a hemispherically symmetric response. Over the region, these wind circulations modify midlevel vertical velocity, moisture flux, and storm tracks, as shown schematically in Fig. 9—these mechanisms appear to be operating in both major regional droughts of the last 50 years, although the relative importance of the three different mechanisms has not yet been evaluated.

Fig. 9.
Fig. 9.

Schematic of drought mechanisms for the 1999–2001 and 2007/08 severe regional droughts.

Citation: Journal of Climate 29, 23; 10.1175/JCLI-D-13-00692.1

d. Regional coherence

While there are at least two major factors that link the region as a whole—the widespread nature of the most severe drought episodes and the importance of cold season synoptic precipitation across most of the region—the amount of regional coherence in year-to-year variability is less clear. To provide a very simple first view of this, annual precipitation is averaged over each country and then correlated with every other country for the 1951–2010 period based on the GPCC data; these cross correlations are shown in Table 1. For clarity, the correlations are shown to only one significant digit, and values equal to or greater than 0.5 are shown in bold. The amount and spatial distribution of station data underlying this analysis change considerably over the period (Hoell et al. 2015), and so, while the results are consistent with previous work, they should be interpreted with some caution. In this calculation with annual data, the northern tier of countries (Uzbekistan, Kyrgyzstan, Turkmenistan, and Tajikistan) is distinct from the others. The countries of the Fertile Crescent are generally closely related but do not clearly form a distinct group; instead, they form a chain of relationships, gradually changing from east to west. Afghanistan is correlated at 0.5 or higher only for Iran, Pakistan, and the United Arab Emirates. Pakistan is correlated at 0.5 or higher only for Afghanistan, which is expected, given the large contribution of the summer monsoon to Pakistan’s precipitation (the mutual correlation is 0.79 considering only the November–April months). Yemen is also correlated at 0.5 or higher only for a single other country in the domain, Oman, which is also expected, given the different precipitation mechanism for the southern tip of the Arabian Peninsula (the African monsoon/ITCZ). The countries of the Arabian Peninsula, in general, are not well correlated to the rest of the region, except for Iran.

From this simple analysis, it appears that none of the domains usually discussed in the literature is a close match to the spatial relationships of precipitation variability, at least in the annual mean, although the entire domain can be coherent in severe episodes. This complexity is consistent with the wide range of regional and large-scale influences on the region, as discussed in the previous three subsections.

For the same period of 1951–2010, the yearly variation in the number of countries with precipitation deficits is shown in Fig. 10 for three deficit thresholds: less than average (light brown), less than 90% of average (medium brown), and less than 75% of average (dark brown). A number of widespread droughts occur during the period, with at least 16 of the 19 countries reporting less-than-average precipitation for 11 of the years (1958, 1960, 1962, 1970, 1973, 1984, 1985, 1990, 2000, 2007, and 2008) and more than half the countries reporting less than 75% of average precipitation for 6 of the years (1970, 1973, 2000, 2001, 2008, and 2010). A composite of the SST anomalies for the 11 yr with at least 16 of 19 countries drier than average is shown in Fig. 11. The pattern of cold SST anomalies in the central and eastern Pacific and warm SST anomalies in the western Pacific and eastern Indian Ocean, as discussed in the previous section relative to severe droughts, holds also for this composite based on the regional coherence of precipitation deficits. The pattern is not sensitive to the choice of deficit threshold or number of countries, although composites that include more of the weaker droughts in the early part of the period have a smaller magnitude of the SST anomalies than composites based on the stronger, more recent droughts.

Fig. 10.
Fig. 10.

Number of countries in the region (of 19 total) experiencing annual precipitation deficits during the 1951–2010 period. The three brown shades (light, medium, and dark) indicate the number of countries with annual precipitation below, 90%, and 75% of average. The calculations are based on GPCC version 6 data on the 0.5° grid, averaged over the land area of each country. The open circles indicate years where at least 16 of the 19 countries had less-than-average precipitation.

Citation: Journal of Climate 29, 23; 10.1175/JCLI-D-13-00692.1

Fig. 11.
Fig. 11.

Composite of SST anomalies (°C) for the 11 yr in the 1951–2010 period when at least 16 of the 19 countries in the region reported annual precipitation less than average (the open circles in Fig. 10), based on the GPCC version 6 precipitation data. The shading interval is 0.1°C and gray stippling is shown over regions not significant at the 5% level.

Citation: Journal of Climate 29, 23; 10.1175/JCLI-D-13-00692.1

In terms of year-to-year variability, the precipitation of individual countries is most closely linked to geographic neighbors with gradual changes in the strength of the relationships over distance. As a result, there do not appear to be clear subdivisions within the region for interannual variability, although the northeastern-most countries show the most separation from the others. In terms of more severe drought, there is considerably more spatial coherence. Given the complexity of these relationships as well as data issues, a careful analysis of the spatial patterns of precipitation variability by season would be useful to determine drought-relevant subdivisions within the region, as well as how best to define the boundaries of the region.

e. Vegetation

Within the semiarid climate zone, which spans a broad swath of the region from the Mediterranean coast in the west to Pakistan in the east, dry seasons and years with below-average precipitation lead to dieback in seasonal grasslands and frequent crop failure in rain-fed agricultural regions (Lotsch et al. 2005; Thenkabail et al. 2004). These lands are also subject to degradation, such as when overgrazing of drought-prone grasslands results in soil nutrient loss and a long-term decline in vegetation cover (Evans and Geerken 2004).

This spatial and temporal variability in vegetation invites consideration of the influence that vegetation might have on the onset and evolution of droughts in the region. Proposed drought–vegetation feedbacks include energy balance feedback pathways mediated by surface albedo (e.g., Charney 1975) or by changes in the Bowen ratio (e.g., Betts and Ball 1998), moisture convergence feedbacks associated with transpiration rate (e.g., Dirmeyer 1994), aerodynamic effects of surface roughness (e.g., Sud et al. 1988), influence on mesoscale atmospheric circulations (e.g., Avissar and Liu 1996), and influence on infiltration of precipitation into the soil (e.g., Scheffer et al. 2005). In drylands, vegetation also has an important soil-stabilizing effect. Loss of vegetation due to climate variability, human-induced land cover change, or land degradation can result in an increase in wind erosion and lofting of dust aerosols into the atmosphere, which can inhibit precipitation by warming and stabilizing the atmosphere and by reducing the amount of solar radiation that reaches the surface. Large portions of southwest Asia are prone to dust storms, suggesting that vegetation influences on dust lofting could have a significant impact on precipitation processes.

While variable vegetation cover and frequent dust storms are signs that southwest Asia could be highly sensitive to vegetation–drought feedbacks, precipitation variability in the region is also largely controlled by powerful large-scale dynamics, as discussed in the previous section. The realization of significant vegetation impacts on drought, then, depends on the relative strength of local versus remote forcings on regional hydrometeorology.

Southwest Asia has not been a particularly strong focus for studies of land–atmosphere feedbacks, but a number of global and regionally focused studies offer insight on potential mechanisms for vegetation–drought feedbacks in the region. Global modeling studies of land–atmosphere coupling strength indicate that portions of southwest Asia have potential for local precipitation feedbacks. Koster et al. (2004) found that modeled coupling strength was weak in arid portions of the region but stronger in some semiarid and subhumid portions of the Arabian Peninsula, Pakistan, Kyrgyzstan, and Tajikistan. This pattern is consistent with results in other regions, which indicate that soil moisture coupling is strongest in transitional climate zones in which soil moisture variability is significantly correlated with changes in evapotranspiration. The Koster et al. (2004) simulations address soil moisture feedbacks, not vegetation feedbacks, and so are not designed to capture the influence that vegetation itself has on albedo, transpiration of subsurface moisture, or surface roughness.

Southwest Asia appears more prominently in a global modeling study by Zeng and Yoon (2009), which used a coupled atmosphere–ocean–land–vegetation model that, when accounting for vegetation albedo effects, indicated that the world’s warm deserts might expand by 34% in the twenty-first century. A significant portion of this expansion was indicated to occur in marginal lands of southwest Asia—primarily in the southern Arabian Peninsula and in the Fertile Crescent and Anatolia regions of Turkey, Syria, and Iraq. In a regional modeling study of drought, Zaitchik et al. (2007) found that under drought conditions vegetation dieback in the semiarid zone of Syria and Iraq leads to an increase in albedo, a reduction in sensible heat flux, and a tendency toward lower surface temperatures, a shallower planetary boundary layer, and reduced cloud cover. In the cooler, generally more humid highlands of Iran, in contrast, drought had no discernible impact on surface albedo, but it did cause a soil-moisture-mediated increase in the Bowen ratio, resulting in elevated surface temperatures and a deep, dry planetary boundary layer that also inhibited cloud formation. Modeling experiments also suggest a feedback on the regional summer monsoon circulation associated with expansion of the Thar Desert (Bollasina and Nigam 2011).

Compared to surface energy balance effects, the potential for vegetation to influence precipitation in southwest Asia through bulk humidity feedbacks would appear to be more modest. Dirmeyer and Brubaker (2007) performed a global evaluation of precipitation recycling, diagnosed through back-trajectory analysis of a global reanalysis dataset, and found that recycling ratios across southwest Asia are among the lowest in the world—generally below 4%, and less than 6% everywhere but in the high mountains of Pakistan. Against this background, it is unlikely that the humidity effects of drought-induced changes in transpiration flux would have a large impact on atmospheric saturation and the potential for precipitation recycling.

f. Dust

Finally, several studies have examined the influence that dust has on meteorological conditions in southwest Asia. The Arabian Peninsula and other arid to semiarid portions of southwest Asia are significant sources of dust aerosols, and the column-integrated dust load over the region is among the highest in the world, particularly in boreal summer (Miller et al. 2004). This dust load results in an increase in atmospheric radiative heating and an associated reduction in solar radiation reaching the surface. The result is a cooler surface and a potential for drought-enhancing feedback due to reduced evapotranspiration or stabilization of the lower atmosphere, though interaction with large-scale dynamics can actually produce a positive precipitation feedback in desert regions like the Arabian Peninsula (Miller et al. 2004</