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Projected Changes in the Annual Cycle of High-Intensity Precipitation Events over West Africa for the Late Twenty-First Century

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  • 1 Competence Center, West African Science Service Center on Climate Change and Adapted Land Use, Ouagadougou, Burkina Faso
  • | 2 Earth System Physics Section, Abdus Salam International Centre for Theoretical Physics, Trieste, Italy
  • | 3 Department of Civil Engineering and Environmental Science, Loyola Marymount University, Los Angeles, California
  • | 4 Competence Center, West African Science Service Center on Climate Change and Adapted Land Use, Ouagadougou, Burkina Faso, and Graduate Research Program on West African Climate System, West African Science Service Center on Climate Change and Adapted Land Use, Akure, Nigeria
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Abstract

In this study, the response of the annual cycle of high-intensity daily precipitation events over West Africa to anthropogenic greenhouse gas for the late twenty-first century is investigated using an ensemble of high-resolution regional climate model experiments. For the present day, the RCM ensemble substantially improves the simulation of the annual cycle for various precipitation statistics compared to the driving Earth system models. The late-twenty-first-century projected changes in mean precipitation exhibit a delay of the monsoon season, consistent with previous studies. In addition, these projections indicate a prevailing decrease in frequency but increase in intensity of very wet events, particularly in the premonsoon and early mature monsoon stages, more pronounced over the Sahel and in RCP8.5 than the Gulf of Guinea and in RCP4.5. This is due to the presence of stronger moisture convergence in the boundary layer that sustains intense precipitation once convection is initiated. The premonsoon season experiences the largest changes in daily precipitation statistics, particularly toward an increased risk of drought associated with a decrease in mean precipitation and frequency of wet days and an increased risk of flood associated with very wet events. Both of these features can produce significant stresses on important sectors such as agriculture and water resources at a time of the year (e.g., the monsoon onset) where such stresses can have stronger impacts. The results thus point toward the importance of analyzing changes of precipitation characteristics as a function of the regional seasonal and subseasonal cycles of rainfall.

Supplemental information related to this paper is available at the Journals Online website: http://dx.doi.org/10.1175/JCLI-D-14-00854.s1.

Corresponding author address: Dr. Mouhamadou Bamba Sylla, WASCAL Competence Center, 06 P.O. Box 9507 Ouagadougou, Burkina Faso. E-mail: syllabamba@yahoo.fr; syllab@wascal.org

Abstract

In this study, the response of the annual cycle of high-intensity daily precipitation events over West Africa to anthropogenic greenhouse gas for the late twenty-first century is investigated using an ensemble of high-resolution regional climate model experiments. For the present day, the RCM ensemble substantially improves the simulation of the annual cycle for various precipitation statistics compared to the driving Earth system models. The late-twenty-first-century projected changes in mean precipitation exhibit a delay of the monsoon season, consistent with previous studies. In addition, these projections indicate a prevailing decrease in frequency but increase in intensity of very wet events, particularly in the premonsoon and early mature monsoon stages, more pronounced over the Sahel and in RCP8.5 than the Gulf of Guinea and in RCP4.5. This is due to the presence of stronger moisture convergence in the boundary layer that sustains intense precipitation once convection is initiated. The premonsoon season experiences the largest changes in daily precipitation statistics, particularly toward an increased risk of drought associated with a decrease in mean precipitation and frequency of wet days and an increased risk of flood associated with very wet events. Both of these features can produce significant stresses on important sectors such as agriculture and water resources at a time of the year (e.g., the monsoon onset) where such stresses can have stronger impacts. The results thus point toward the importance of analyzing changes of precipitation characteristics as a function of the regional seasonal and subseasonal cycles of rainfall.

Supplemental information related to this paper is available at the Journals Online website: http://dx.doi.org/10.1175/JCLI-D-14-00854.s1.

Corresponding author address: Dr. Mouhamadou Bamba Sylla, WASCAL Competence Center, 06 P.O. Box 9507 Ouagadougou, Burkina Faso. E-mail: syllabamba@yahoo.fr; syllab@wascal.org

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