A unifying view of climate change in the Sahel linking intra-seasonal, interannual and longer time scales

We propose a re-interpretation of the oceanic influence on the climate of the African Sahel that is consistent across observations, 20th century simulations and 21st century projections, and that resolves the uncertainty in projections of precipitation change in this region: continued warming of the global tropical oceans increases the threshold for convection, potentially drying tropical land, but this ‘upped ante’ can be met if sufficient moisture is supplied in monsoon flow. In this framework, the reversal to warming of the subtropical North Atlantic, which is now out-pacing warming of the global tropical oceans, provides that moisture, and explains the partial recovery in precipitation since persistent drought in the 1970s and 1980s. We find this recovery to result from increases in daily rainfall intensity, rather than in frequency, most evidently so in Senegal, the westernmost among the three Sahelian countries analyzed. Continuation of these observed trends is consistent with projections for an overall wetter Sahel, but more variable precipitation on all time scales, from intra-seasonal to multi-decadal.

[1]  P. Lamb.  Large-scale Tropical Atlantic surface circulation patterns associated with Subsaharan weather anomalies , 1978 .

[2]  Peter J. Lamb,et al.  Persistence of Subsaharan drought , 1982, Nature.

[3]  S. Nicholson.  Sub-Saharan Rainfall in the Years 1976–80: Evidence of Continued Drought , 1983 .

[4]  T. Palmer,et al.  Sahel rainfall and worldwide sea temperatures, 1901–85 , 1986, Nature.

[5]  Michael H. Glantz,et al.  Anatomy of a rainfall index , 1986 .

[6]  R. Koster,et al.  Sources of Sahel Precipitation for Simulated Drought and Rainy Seasons , 1989 .

[7]  Thomas M. Smith,et al.  Improved Global Sea Surface Temperature Analyses Using Optimum Interpolation , 1994 .

[8]  Balaji Rajagopalan,et al.  Analyses of global sea surface temperature 1856–1991 , 1998 .

[9]  Leon D. Rotstayn,et al.  Tropical Rainfall Trends and the Indirect Aerosol Effect , 2002 .

[10]  John C. H. Chiang,et al.  Tropical tropospheric temperature variations caused by ENSO and their influence on the remote tropical climate , 2002 .

[11]  Dominique Tapsoba,et al.  Rainfall Variability in West Africa during the Years 1950-90 , 2002 .

[12]  J. Neelin,et al.  Tropical drought regions in global warming and El Niño teleconnections , 2003 .

[13]  Elizabeth C. Kent,et al.  Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century , 2003 .

[14]  R. Saravanan,et al.  Oceanic Forcing of Sahel Rainfall on Interannual to Interdecadal Time Scales , 2003, Science.

[15]  Bradfield Lyon,et al.  The strength of El Niño and the spatial extent of tropical drought , 2004 .

[16]  J. Neelin,et al.  Mechanisms of global warming impacts on regional Tropical precipitation , 2004 .

[17]  T. D. Mitchell,et al.  An improved method of constructing a database of monthly climate observations and associated high‐resolution grids , 2005 .

[18]  C. Reij,et al.  Changing land management practices and vegetation on the Central Plateau of Burkina Faso (1968-2002) , 2005 .

[19]  Alessandra Giannini,et al.  Robust Sahel drying in response to late 20th century forcings , 2006 .

[20]  H. Douville,et al.  On the tropical origin of uncertainties in the global land precipitation response to global warming , 2006 .

[21]  Andrew W. Robertson,et al.  Seasonal Predictability and Spatial Coherence of Rainfall Characteristics in the Tropical Setting of Senegal , 2006 .

[22]  B. Soden,et al.  Robust Responses of the Hydrological Cycle to Global Warming , 2006 .

[23]  K. Cook,et al.  Coupled Model Simulations of the West African Monsoon System: Twentieth- and Twenty-First-Century Simulations , 2006 .

[24]  Adam A. Scaife,et al.  Climate impacts of the Atlantic Multidecadal Oscillation , 2006 .

[25]  S. Solomon.  The Physical Science Basis : Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change , 2007 .

[26]  John F. B. Mitchell,et al.  THE WCRP CMIP3 Multimodel Dataset: A New Era in Climate Change Research , 2007 .

[27]  Roger Jones,et al.  Regional climate projections , 2007 .

[28]  A. Sobel,et al.  SST Forcings and Sahel Rainfall Variability in Simulations of the Twentieth and Twenty-First Centuries , 2008 .

[29]  J. B. Opschoor,et al.  Fighting climate change: Human solidarity in a divided world , 2007 .

[30]  Gabriel A. Vecchi,et al.  Whither Hurricane Activity? , 2008, Science.

[31]  C. Mbow,et al.  Urban sprawl development and flooding at Yeumbeul suburb (Dakar-Senegal) , 2008 .

[32]  Vincenzo Artale,et al.  Mediterranean water cycle changes: transition to drier 21st century conditions in observations and CMIP3 simulations , 2008 .

[33]  A. Tougiani,et al.  Community mobilisation for improved livelihoods through tree crop management in Niger , 2009 .

[34]  C. Roncoli,et al.  Local perceptions and regional climate trends on the Central Plateau of Burkina Faso , 2008 .

[35]  Abdou Ali,et al.  The Sahelian standardized rainfall index revisited , 2009 .

[36]  J. Overpeck,et al.  Atlantic Forcing of Persistent Drought in West Africa , 2009, Science.

[37]  A. Sobel,et al.  The Role of the Sahara Low in Summertime Sahel Rainfall Variability and Change in the CMIP3 Models , 2009 .

[38]  Arthur M. Greene,et al.  Drought return times in the Sahel: A question of attribution , 2009 .

[39]  A. Sobel,et al.  Delayed Sahel rainfall and global seasonal cycle in a warmer climate , 2009 .

[40]  J. Neelin,et al.  Tropical South America–Atlantic Sector Convective Margins and Their Relationship to Low-Level Inflow , 2010 .

[41]  A. Giannini.  Mechanisms of Climate Change in the Semiarid African Sahel: The Local View , 2010 .

[42]  S. Xie,et al.  Changes in the sea surface temperature threshold for tropical convection , 2010 .

[43]  P. Jones,et al.  A comparison of large scale changes in surface humidity over land in observations and CMIP3 general circulation models , 2010 .

[44]  S. Camargo,et al.  Enhanced spring convective barrier for monsoons in a warmer world? , 2011 .

[45]  Prashant D. Sardeshmukh,et al.  Critical influence of the pattern of Tropical Ocean warming on remote climate trends , 2011 .

[46]  O. Ndiaye,et al.  Predictability of Seasonal Sahel Rainfall Using GCMs and Lead-Time Improvements Through the Use of a Coupled Model , 2011 .

[47]  Michael F. Wehner,et al.  Sulfate Aerosol Control of Tropical Atlantic Climate over the Twentieth Century , 2011 .

[48]  Nicolas Bellouin,et al.  Aerosols implicated as a prime driver of twentieth-century North Atlantic climate variability , 2012, Nature.

[49]  Karl E. Taylor,et al.  An overview of CMIP5 and the experiment design , 2012 .

[50]  K. Cook,et al.  Role of the West African Westerly Jet in Sahel Rainfall Variations , 2012 .

[51]  J. Chiang,et al.  Coordinated Abrupt Weakening of the Eurasian and North African Monsoons in the 1960s and Links to Extratropical North Atlantic Cooling , 2012 .

[52]  A. Giannini,et al.  Changes in seasonal descriptors of precipitation in Burkina Faso associated with late 20th century drought and recovery in West Africa , 2013 .

[53]  A. Giannini,et al.  Oceanic influence on the sub-seasonal to interannual timing and frequency of extreme dry spells over the West African Sahel , 2013, Climate Dynamics.

[54]  A. Challinor,et al.  Implications of regional improvement in global climate models for agricultural impact research , 2013 .

[55]  Corinne Le Quéré,et al.  Climate Change 2013: The Physical Science Basis , 2013 .