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

indicating that a more realistic representation of surface conditions reduces model biases, many current numerical models, particularly those used for operational forecasts, still employ fixed land-cover types. Hence, they are unable to represent the additional sources of interannual variability owing to land-cover changes, as a result of either land-use changes or the vegetation’s degree of stress (e.g., during droughts, wet periods, or insect outbreaks). In other words, models that do not include

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

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

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Richard Seager and Martin Hoerling

relative to natural internal variability of the atmosphere alone and to its limited detectability as of now, consistent with the conclusions of Sheffield and Wood (2008) . Lastly, it is instructive to compare how large the current climate change signal is relative to a signal associated with natural oceanic boundary forcings. For the 2011 and 2012 droughts, for instance, the natural ocean-forced signal is about a factor of 5 greater than the signal of long-term change. It is also important to

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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

drought. Many drought research studies have focused on particular regions or selected events, whereas others have examined the global distribution of droughts, their forcing factors, and their predictability. Efforts in operational environments now routinely assess current and future drought conditions over a variety of temporal and spatial scales. This broad range of activities, as well as many drought impact studies, suggests a need to document our collective understanding of and capabilities to

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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

) Leading mode of (c) tropical Atlantic SST from February–May (FMAM) to September–December (SOND) and (d) summer June–September (JJAS) precipitation over West Africa during the period 1979–2003. Only summer (left) SST and (right) precipitation (std dev in mm) patterns have been shown. Red colors are positive (negative) for the SST (precipitation) fields. Figure modified from Polo et al. (2008) . Most current state-of-the-art atmospheric GCMs (AGCMs) are able to capture the links between SST anomalies

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

slowly varying ocean boundary conditions contributed substantially to the magnitude of the event. They also stated that “severe drought occurred with the Russian heat wave, making it likely that land surface feedbacks amplified this heat wave’s intensity.” Trenberth and Fasullo (2012) , in contrast, linked the unusual anticyclone to the development of a large-scale Rossby wave train—suggesting that the wave train was forced by anomalous convection in the tropical Atlantic and northern Indian Oceans

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Bradfield Lyon

deleterious consequences it is not surprising that across the Greater Horn, where rain-fed agriculture is the mainstay, where food security is often threatened ( Funk et al. 2008 ; Funk and Brown 2009 ), and where the largest contribution to electricity generation is hydropower ( Kaunda et al. 2012 ), that drought information is especially valued. Nor is the interest in drought information limited to assessments of current conditions or the provision of seasonal forecasts. Seemingly contradictory signals

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Lixia Zhang and Tianjun Zhou

1970s, aridity over north China has increased substantially, and the extreme drought frequency is increasing in the central part of northern China, northeast China, and the eastern part of northwest (NW) China ( Ma and Fu 2006 ). Because of the increasing drought, the grassland area of Jilin Province (41°–46°N, 122°–131°E) is decreasing at a rate of 2.8% per year, the semiarid boundary of northern China has shifted southeastward during the last 50 years (1950–98), and the discharge of the Yellow

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