Consistency of projected drought over the Sahel with changes in the monsoon circulation and extremes in a regional climate model projections

Received 9 August 2009; revised 7 January 2010; accepted 15 February 2010; published 21 August 2010. [1] As a step toward an increased understanding of climate change over West Africa, in this paper we analyze the relationship between rainfall changes and monsoon dynamics in high‐resolution regional climate model experiments performed using the Regional Climate Model (RegCM3). Multidecadal simulations are carried out for present‐day and future climate conditions under increased greenhouse gas forcing driven by the global climate model European Center/Hamburg 5 (ECHAM5). Compared to the present day, the future scenario simulation produces drier conditions over the Sahel and wetter conditions over orographic areas. The Sahel drying is accompanied by a weaker monsoon flow, a southward migration and strengthening of the African Easterly Jet, a weakening of the Tropical Easterly Jet, a decrease of the deep core of ascent between the jets, and reduced African Easterly Wave activity. These circulation changes are characteristics of dry periods over the Sahel and are similar to the conditions found in the late twentieth century observed drought over the region. Changes in extreme events suggest that the drier conditions over the Sahel are associated with more frequent occurrences of drought periods. The projected drought over the Sahel is thus physically consistent with changes in the monsoon circulation and the extreme indices (maximum dry spell length and 5 day precipitation).

[1]  F. Giorgi,et al.  Development of a Second-Generation Regional Climate Model (RegCM2). Part I: Boundary-Layer and Radiative Transfer Processes , 1993 .

[2]  S. Janicot,et al.  Composite patterns of easterly disturbances over West Africa and the tropical Atlantic: a climatology from the 1979–95 NCEP/NCAR reanalyses , 2001 .

[3]  Luis Kornblueh,et al.  The atmospheric general circulation model ECHAM5 Part II: Sensitivity of simulated climate to horizontal and vertical resolution , 2004 .

[4]  J. McGregor,et al.  Climate change simulations of Tasmanian precipitation using multiple nesting , 1994 .

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

[6]  Erika Coppola,et al.  The Regional Climate Change Hyper-Matrix Framework , 2008 .

[7]  A. Diedhiou,et al.  Investigating the West African Climate System Using Global/Regional Climate Models , 2002 .

[8]  Linda O. Mearns,et al.  Analysis of daily variability of precipitation in a nested regional climate model: comparison with observations and doubled CO2 results , 1995 .

[9]  Mike Hulme,et al.  Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/joc.1083 COMMENT THE RECENT SAHEL DROUGHT IS REAL , 2004 .

[10]  F. Giorgi,et al.  Introduction to special section : Regional climate modeling revisited , 1999 .

[11]  Sharon E. Nicholson,et al.  Land surface processes and Sahel climate , 2000 .

[12]  Guiling Wang,et al.  Ecosystem dynamics and the Sahel Drought , 2000 .

[13]  James W. Hurrell,et al.  Detection and Attribution of Twentieth-Century Northern and Southern African Rainfall Change , 2006 .

[14]  B. Fontaine,et al.  Wind-Field Coherence and Its Variations over West Africa , 1992 .

[15]  W. Collins,et al.  Global climate projections , 2007 .

[16]  F. Giorgi,et al.  Regional Climate Change Scenarios over the United States Produced with a Nested Regional Climate Model , 1994 .

[17]  F. Giorgi,et al.  Simulation of the intraseasonal and the interannual variability of rainfall over West Africa with RegCM3 during the monsoon period , 2010 .

[18]  K. Cook.  Generation of the African Easterly Jet and Its Role in Determining West African Precipitation , 1999 .

[19]  J. Pal,et al.  Projected changes in mean and extreme precipitation over the Mediterranean region from a high resolution double nested RCM simulation , 2006 .

[20]  Raquel V. Francisco,et al.  Regional Climate Modeling for the Developing World: The ICTP RegCM3 and RegCNET , 2007 .

[21]  W. Landman.  Climate change 2007: the physical science basis , 2010 .

[22]  S. Nicholson.  The intensity, location and structure of the tropical rainbelt over west Africa as factors in interannual variability , 2008 .

[23]  H. Paeth,et al.  Regional modelling of future African climate north of 15°S including greenhouse warming and land degradation , 2007 .

[24]  J. P. Grist.  Easterly waves over Africa. Part I: The seasonal cycle and contrasts between wet and dry years , 2002 .

[25]  Luca Bonaventura,et al.  The atmospheric general circulation model ECHAM 5. PART I: Model description , 2003 .

[26]  Michael Botzet,et al.  Ocean Circulation and Tropical Variability in the Coupled Model ECHAM5/MPI-OM , 2006 .

[27]  M. Blackburn,et al.  Maintenance of the African easterly jet , 1999 .

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

[29]  Alexei G. Sankovski,et al.  Special report on emissions scenarios , 2000 .

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

[31]  P. Lamb,et al.  Further case studies of tropical Atlantic surface atmospheric and oceanic patterns associated with sub-Saharan drought , 1992 .

[32]  A. Gaye,et al.  Evaluating the National Center for Atmospheric Research climate system model over West Africa: Present‐day and the 21st century A1 scenario , 2005 .

[33]  N. D’AMATOa,et al.  ON THE CHARACTERISTICS OF THE RAINFALL EVENTS IN THE SAHEL WITH A VIEW TO THE ANALYSIS OF CLIMATIC VARIABILITY , 1998 .

[34]  Richard G. Jones,et al.  Global high resolution versus Limited Area Model climate change projections over Europe: quantifying confidence level from PRUDENCE results , 2005 .

[35]  F. Semazzi,et al.  The role of orography in determining the Sahelian climate , 1997 .

[36]  Sharon E. Nicholson,et al.  A conceptual model for understanding rainfall variability in the West African Sahel on interannual and interdecadal timescales , 2001 .

[37]  Xindi Bian,et al.  Mid-Century Ensemble Regional Climate Change Scenarios for the Western United States , 2004 .

[38]  J. Pal,et al.  High-resolution simulations of West African climate using regional climate model (RegCM3) with different lateral boundary conditions , 2009 .

[39]  H. Douville,et al.  African monsoon teleconnections with tropical SSTs: validation and evolution in a set of IPCC4 simulations , 2007 .

[40]  F. Giorgi,et al.  Addressing climate information needs at the regional level: the CORDEX framework , 2009 .

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

[42]  J. Christensen,et al.  Climate modelling: Severe summertime flooding in Europe , 2003, Nature.

[43]  F. Giorgi,et al.  An intercomparison of regional climate simulations for Europe: assessing uncertainties in model projections , 2007 .

[44]  Impact of warm ENSO events on atmospheric circulation and convection over the tropical Atlantic and West Africa , 1997 .

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

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

[47]  C. Thorncroft,et al.  Intense convective systems in West Africa and their relationship to the African easterly jet , 2006 .

[48]  J. Pal,et al.  Simulation of West African monsoon using RegCM3 Part II: impacts of deforestation and desertification , 2008 .

[49]  Jeremy S. Pal,et al.  Land surface coupling in regional climate simulations of the West African monsoon , 2009 .

[50]  F. Giorgi,et al.  Development of a Second-Generation Regional Climate Model (RegCM2). Part II: Convective Processes and Assimilation of Lateral Boundary Conditions , 1993 .

[51]  Jeremy S. Pal,et al.  Consistency of recent European summer precipitation trends and extremes with future regional climate projections , 2004 .

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

[53]  B. Machenhauer,et al.  Very High-Resolution Regional Climate Simulations over Scandinavia—Present Climate , 1998 .

[54]  A. Gaye,et al.  Late 20th century attribution of drying trends in the Sahel from the Regional Climate Model (RegCM3) , 2005 .

[55]  T. Delworth,et al.  Oceanic forcing of the late 20th century Sahel drought , 2005 .