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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

multiyear drought (e.g., beyond the ENSO time scale), and one may wonder whether such droughts result from naturally occurring decadal modes of variability [e.g., the Atlantic multidecadal oscillation (AMO) and Pacific decadal oscillation (PDO)], from decadal changes in the relationships between interannual modes of variability [e.g., ENSO and Atlantic El Niños ( Losada et al. 2012 )], from global warming ( Mohino et al. 2011a ), or from no mechanism at all (i.e., from a simple random sequence of dry

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Bradfield Lyon

central Indian Ocean that has been observed over the past several decades. Meanwhile, there is a strong consensus among climate model projections that the long rains will increase during the current century in response to anthropogenic greenhouse gas forcing ( Christensen et al. 2007 ; Shongwe et al. 2011 ). Is the post-1998 increase in drought frequency during MAM associated with long-term climate change or something else? What is the role of decadal variability in modulating drought occurrence

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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

number of papers per year. The dates of some of the most remarkable international projects studying the Sahelian climate variability are marked in the figure. The rainy season in the Sahel has large interannual and decadal variations. A substantial part of this variability is due to the influence of slowly varying climate subcomponents, such as sea surface temperatures (SSTs) and land surface conditions. The importance of oceanic influences at interannual and decadal time scales has been supported by

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

provides more details on these and several other of the more popular metrics. The overall character of northern Eurasian precipitation and temperature variability and its relationship to drought and heat waves is now examined. Figure 1 (left panels) shows the variance of June–August (JJA) mean precipitation for the last three decades (1979–2012) as determined by two different reanalyses and from an analysis of station observations. While there are some differences, there is general agreement that the

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Richard Seager and Martin Hoerling

, of where we stand in terms of understanding the causes and mechanisms of North American droughts and to what extent we can anticipate hydroclimate variability and change and, in particular, droughts in the coming seasons to decades. This review is being performed under the auspices of the Global Drought Information System (GDIS) which is under the World Climate Research Programme (WCRP) umbrella. Hence we aim to contribute to challenges identified at the July 2012 WCRP meeting, including, under

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

( Ummenhofer et al. 2009 ). The weak spring rainfall decline does, however, display coherence with an intensification in the subtropical ridge ( Timbal and Drosdowsky 2013 , and references therein). Spring rainfall is also linked to trends and variability in the IOD ( Ummenhofer et al. 2009 ), which has displayed an unprecedentedly high frequency of positive events during recent decades ( Ihara et al. 2008 ; Abram et al. 2008 ; Cai et al. 2009b ). High numbers of positive IOD events tend to be associated

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Lixia Zhang and Tianjun Zhou

global land monsoon precipitation has experienced a declining trend during the second half of the twentieth century ( B. Wang and Q. Ding 2006 ). This trend is actually an interdecadal variability driven by the phase transition of the Pacific decadal oscillation (PDO) ( Zhou et al. 2008a , 2013 ). The phase transition of PDO changed from negative to positive phase around the end of 1970s ( Fig. 10a ). The correlation between the observed EASMI and PDO is 0.62, statistically significant at the 5

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

Niña with warm waters in the western Pacific and eastern Indian Oceans, appears to play the strongest role in forcing regionwide drought, including the two most severe of the last 50 years—1999–2001 and 2007/08. The relative role of the western Pacific Ocean compared to the eastern Indian Ocean in these episodes, as well as the relationship of those regions to decadal variability and trends, particularly in terms of how other modes can contribute to the cold central Pacific–warm western Pacific

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

1. Introduction Land surface processes are recognized as a potential source of climate variability and predictability at different time scales, from hours to seasons and longer ( Koster et al. 2000 ; Koster and Suarez 2003 ; Guo et al. 2011 ; Sellers et al. 1992 ; Foley et al. 2000 ). Changes in the land surface or vegetation cover can affect the way the land and the atmosphere interact at many of those time scales and can thus have an effect on climate. Changes in the surface states result

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