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Belen Rodríguez-Fonseca, Elsa Mohino, Carlos R. Mechoso, Cyril Caminade, Michela Biasutti, Marco Gaetani, J. Garcia-Serrano, Edward K. Vizy, Kerry Cook, Yongkang Xue, Irene Polo, Teresa Losada, Leonard Druyan, Bernard Fontaine, Juergen Bader, Francisco J. Doblas-Reyes, Lisa Goddard, Serge Janicot, Alberto Arribas, William Lau, Andrew Colman, M. Vellinga, David P. Rowell, Fred Kucharski, and Aurore Voldoire

the results of several studies ( Folland et al. 1986 ; Palmer 1986 ; Rowell et al. 1992 ; Ward 1998 ; Camberlin et al. 2001 ; Giannini et al. 2003 ; Lu and Delworth 2005 ; Cook 2008 ; Caminade and Terray 2010 ; Losada et al. 2010 ; Rodríguez-Fonseca et al. 2011 ; Mohino et al. 2011a ; Rowell 2013 ; Nicholson 2013 ). Other studies have addressed the effects of land–atmosphere interactions ( Xue, 1997 ; Zeng et al. 1999 ; Nicholson 2000 ; Giannini et al. 2003 ; Yoshioka et al. 2007

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Bradfield Lyon

are emerging regarding drought on longer time scales, particularly in eastern Ethiopia, Kenya, Somalia, and north-central Tanzania. Since 1999 there has been a substantial decline in the March–May (MAM) “long rains,” inevitably leading to speculation over the possible role of anthropogenic climate change ( Lyon and DeWitt 2012 ). Some studies (e.g., Funk et al. 2008 ) have suggested that the long rains decline has been occurring over a longer period, and link it to an upward trend of SSTs in the

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Siegfried D. Schubert, Ronald E. Stewart, Hailan Wang, Mathew Barlow, Ernesto H. Berbery, Wenju Cai, Martin P. Hoerling, Krishna K. Kanikicharla, Randal D. Koster, Bradfield Lyon, Annarita Mariotti, Carlos R. Mechoso, Omar V. Müller, Belen Rodriguez-Fonseca, Richard Seager, Sonia I. Seneviratne, Lixia Zhang, and Tianjun Zhou

forcing for some of these large-scale motions is known to include sea surface temperature (SST) anomalies, land (especially soil moisture) feedbacks, aerosols, and other natural and anthropogenic changes in radiative forcing such as those associated with global warming. These forcings are important because they may provide some degree of drought predictability (e.g., Smith et al. 2012 ). It must be kept in mind, however, that there is a substantial unforced (i.e., driven by processes internal to the

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Lixia Zhang and Tianjun Zhou

forcing ( Duan and Wu 2008 ) and anthropogenic forcing agents including aerosols ( Menon et al. 2002 ; Wang et al. 2013 ) have also been suggested as mechanisms that have driven the long-term monsoon and thereby drought changes over East Asia. A regional model study on land-use effects showed that the land use modified by anthropogenic activities may result in a reduction of precipitation and an increase of temperature over north China ( Gao et al. 2007 ). A recent analysis of 17 models from phase 5

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Richard Seager and Martin Hoerling

greenhouse gases (e.g., CO 2 , CH 4 , NO 2 , O 3 , and CFCs) are specified. The CAM4 runs also specify varying anthropogenic, solar, and volcanic aerosols. In these two cases the SST histories used to force the model include not only SST variability arising from ocean dynamics (e.g., ENSO) and atmospheric forcing but also the response to natural and anthropogenic radiative forcing. This motivates our fourth ensemble: To address possible effects of long-term climate change on U.S. drought variability

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Omar V. Müller, Ernesto Hugo Berbery, Domingo Alcaraz-Segura, and Michael B. Ek

from land-use and land-cover changes, either from natural or anthropogenic origin or from climate conditions that affect the vegetation health and its phenology. Abundant evidence based on model simulations has been offered on the impacts of land-cover changes on regional to global climate and will not be reviewed here (see, e.g., Pielke et al. 2007 , and references therein; Mahmood et al. 2010 ). The need for a correct representation of the land surface in models has been discussed for many

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Wenju Cai, Ariaan Purich, Tim Cowan, Peter van Rensch, and Evan Weller

climate models forced by natural and anthropogenic factors that induce climate change. This approach is useful because variability-induced trends, although present in individual models, are independent from model to model. Thus, a MMEA largely removes natural variability (e.g., Purich et al. 2013 ), to give a climate change estimate, common across all models. The MMEA approach is also applied to calculate decadal regional rainfall averages and long-term trends that are congruent with trends in the

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Mathew Barlow, Benjamin Zaitchik, Shlomit Paz, Emily Black, Jason Evans, and Andrew Hoell

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

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Siegfried D. Schubert, Hailan Wang, Randal D. Koster, Max J. Suarez, and Pavel Ya. Groisman

, indicating the effects of land–atmosphere feedback. The role of SST in seasonal to decadal climate variability over Eurasia is also still not well understood. Again, much of the analysis of the role of SST has focused on impacts in Europe, although a number of these studies have implications for regions to the east. Ionita et al. (2012) analyzed the self-calibrating Palmer drought index ( van der Schrier et al. 2006 ) for the period 1901–2002 and found considerable interannual and multidecadal

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