Potential impacts of forestation on heatwaves over West Africa in the future

Previous studies have projected future climate change impacts on heatwaves in West Africa, but without including the influence of ongoing forestation activities in the region. The present study investigates how the ongoing forestation activities in West Africa may influence the characteristics of heatwaves over the region in the future. The study characterised heatwave using two metrics (excess heat factor (EHF), and a percentile based index (TXI)). A regional climate model (RegCM) is used to simulate characteristics of heatwave for the past (1970-2000) and future (2030-2060; IPCC RCP4.5) climates in West Africa with and without forestation of the Savannah zone (area between 8°N and 12°N). While RegCM gives a realistic simulation of extreme temperature thresholds (i.e. 95th percentile of daily mean temperature and 90th percentile of daily maximum temperature) and seasonal distribution of heatwave days, it fails to reproduce the spatial distribution of heatwave number, days and duration as in observation. Both heatwave indices (TXI and EHF) generally show similar patterns of heatwave characteristics over West Africa, except that heatwave number and days are substantially greater with TXI than with EHF. The results show that the RCP 4.5 emission scenario would induce longer and more frequent heatwave events and days over the whole region and that the increase of heatwave days is likely to occur in all months of the year. The results further indicate that forestation, on the average, may increase the number of heatwave events and days over the forested zone (Savannah), and decrease them over the Sahel and along the Guinea coast. This study has application in the use of large scale forestation activities as a climate change mitigation option in West Africa.