On the Impact of Land Use and Land Cover Change on the West African Monsoon: Approach and Results from the WAMME Inter-comparison Project

Aaron Anthony Boone, CNRM, Université de Toulouse, Météo-France, CNRS, GMME, Toulouse, France, Yongkang Xue, University of California, Los Angeles (UCLA), Department of Geography, Los Angeles, United States, Comer Ruth, UKMetOffice, Exeter, United Kingdom, Dr. Fernando De Sales, PhD., UCLA, Geography, Los Angeles, CA, United States, Samson M Hagos, Pacific Northwest National Laboratory, Richland, WA, United States, Sarith P P Mahanama, NASA/GSFC, Greenbelt, MD, United States, Ibrah Sanda, AGRHYMET, Niamey, Nigeria, Kathleen A. Schiro, UCLA, Atmospheric Sciences, Los Angeles, United States, Guoqiong Song, University of California Los Angeles, Los Angeles, CA, United States, Guiling Wang, University of Connecticut, Groton, CT, United States, Randal D Koster, NASA Goddard SFC, Global Modeling and Assimilation Office, Greenbelt, United States and Carlos R Mechoso, University of California Los Angeles, Department of Atmospheric and Oceanic Sciences, Los Angeles, CA, United States

Contact First Author: Aaron Anthony Boone; aaron.boone@meteo.fr

Previously Published Material: Initial finding were presented at the AGU (Dec, 2014). More detailed multi-model analysis has been done for this talk

Abstract ID#: 35554

 

English Abstract:
The population of the Sahel region of West Africa has approximately doubled in the past 50 years, and could potentially double again by the middle of this century. This has lead to the northward expansion of agricultural areas at the expense of savannah, leading to widespread land use-land cover change (LULCC). Because there is strong evidence of significant surface-atmosphere coupling in this region, one of the main goals of the West African Monsoon Modeling and Evaluation (WAMME) project phase 2 is to provide a basic understanding of LULCC on the regional climate, and to evaluate the sensitivity of the seasonal variability of the WAM to LULCC. The prescribed LULCC is based on a recent 50 year period using the latest available information, and it is applied to 5 state of the art global climate models over a 5 year period. Previous multi-model LULCC studies show large model spread. Because land cover maps and surface parameters can vary widely among models, we sought to impose similar biogeophysical responses to LULCC using a simple experimental setup. The overall impact is a 20-40 % reduction in annual rainfall in the Sahel and a southward shift of the monsoon. In most of the models, the main factor causing diabatic cooling of the upper troposphere and enhanced subsidence over the region of LULCC is the reduction of convective heating rates linked to reduced latent heat flux and moisture flux convergence. The change in radiative heating rate was found to be a secondary process. For most of the models, the LULCC evokes a precipitation dipole pattern which is consistent with the observed pattern for dry climate anomalies over this region. In broad agreement with previous studies, the impact of degradation on the regional climate is found to be variable among the models, however, the signal is stronger and more consistent here which is likely related to our emphasis on prioritizing a consistent impact of LULCC on the surface biophysical properties.
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