The impact of deforestation on climate in Sahelian West Africa

Abstract

The extent of land cover (vegetation) was assessed by comparing the preindustrial period to the present, using a fully coupled regional atmospheric model (WRF) and a land surface model (Noah-MP) with dynamic vegetation, applied at a 15 km horizontal resolution over Sahelian West Africa. Policy brief, January 2025; Warming and Drought Impacts in Sahelian West Africa 2

The impact of deforestation on mean and extreme climate indices (temperature and precipitation) was evaluated using the same models and approach. Additionally, a bias assessment was conducted to validate the model. This model is considered one of the most advanced tools currently available for climate change assessment. The extent of land cover change (LCC) exhibits significant spatial variability across the Sahelian West African region, as shown (Figure 1) by the fully coupled climate model (WRF) and land surface model (Noah-MP), with an average change of approximately 19%. These analyses capture the effects of land cover modifications on the region's surface characteristics. The most substantial changes were observed in the region's eastern part, where the LCC fraction reached up to 45%. This indicates considerable land cover Figure 2 highlights the regional changes in temperature and rainfall/precipitation (mean and extreme indices) in response to LCC from preindustrial times to the present (2022). For temperature (Figure 2a), the region experiences a warming effect of up to +2°C in maximum temperature and +1.5°C in the extreme indices (TNx) due to anthropogenic LCC. Similarly, rainfall has decreased by up to -0.5 mm/day, and the number of wet days (R1mm) has been reduced by up to -10 days/y in response to LCC (Figure 2b). The regional relative contribution of LCC has a greater negative impact on extreme temperatures and rainfall than on mean conditions (see Figure 3). Furthermore, extreme temperatures are affected more significantly than extreme rainfall. For example, LCC has significantly increased land surface temperature by up to +3.8%, as reflected in the rise in the number of tropical nights (TR, defined as days when the minimum daily temperature exceeds 20 °C). On the other hand, extreme rainfall is also negatively affected, contributing to an increase in consecutive dry days (CDD, defined as consecutive days with rainfall < 1 mm), while simultaneously increasing the frequency of very heavy rainfall days and the simple daily intensity index (SDII, defined as the average rainfall on wet days with rainfall ≥ 1 mm.