Effects of Land Cover Changes on Compound Extremes over West Africa Using the Regional Climate Model RegCM4

Moctar Camara,Ibrahima Diba,Arona Diedhiou

doi:10.3390/atmos13030421

Abstract

This study aims to characterize the impacts of the Sahel–Sahara interface reforestation on compound extremes in the Sahel region during the West African monsoon season (June–July–August–September, JJAS). For this purpose, we performed a simulation with the standard version of the RegCM4 model, and another simulation with the altered version of the same model, taking into account the incorporated forest. Results show that reforestation may strongly influence the frequency of individual extreme events (dry and warm days) by decreasing them over and off the reforested zone. The reduction in these extreme dry and warm days may be due partly to the strengthening of the atmospheric moisture content over most parts of the West African domain and the weakening of the sensible heat flux south of 16° N. The analysis also shows an increase in extreme wet days over and off the reforested zone, which could be associated partly with the strengthening of evapotranspiration over most parts of the West African domain, including the reforested area. The analysis of compound extremes shows a strong occurrence of the compound dry/warm mode over the northern Sahel for both runs, probably due to the weak precipitation recorded in this zone. Both experiments also simulated a strong compound wet/warm mode occurrence over the Sahel due to a high rainfall occurrence over this region. When comparing both runs, the impact of the reforestation was to decrease (increase) the compound extreme dry/warm (wet/warm) mode over the reforested zone. The dry/warm mode decrease is consistent with that of individual extreme dry and warm days, while the compound wet/warm mode increase may be driven by that of the extreme wet days. Finally, when considering the seasonal cycle, the dry/warm mode exhibits a more substantial decrease in the beginning (June–July, JJ) than during the peak of the West African summer monsoon season (August–September, AS). Moreover, reforestation similarly affects the compound wet/warm mode in JJ and AS by increasing it in the reforested region and decreasing it over the Southern Sahel (south of 15° N). This work suggests that reforestation may be a good solution for West African policymakers to mitigate climate change over the region and to develop better strategies for water resource management.

Highlights

An increase in the frequency of extreme weather events in this region could negatively affect socio-economic activities, especially in the agriculture sector, which is highly dependent on the West African monsoon rainfall [5]
The analysis showed an increase in extreme wet days over and off the reforested zone during the JJAS period (Figure 6c), which could be associated partly with the strengthening of evapotranspiration (Figure 3c) over most parts of the West African domain
We studied the impacts of the reforestation at the Sahel–Sahara interface

Summary

Introduction

According to the special report of the Intergovernmental Panel on Climate Change [1], the global average temperature has increased by 0.05 ◦ C from 1998 to 2012. This global warming is accompanied by an increase in extreme weather events. An increase in the frequency of extreme weather events in this region could negatively affect socio-economic activities, especially in the agriculture sector, which is highly dependent on the West African monsoon rainfall [5]. The degradation of the environment, that of plant cover, remains a major concern in West Africa. Many studies [6–8] have shown that this degradation of vegetation cover is due to human activities and climatic variations. Béné and Fournier and Ozer et al [9,10] have shown that human activity constantly damages the environment

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Results

Conclusion