Results from a study carried out by scientists from World Agroforestry (ICRAF), Swedish University of Agricultural Sciences (SLU) and Université de Ouagadougou indicate that West Africa will experience an increase in the number of extreme rainfall events in the 21st century, thanks to climate change.
These results of the study funded by the Swedish Research Council (Vetenskapsrådet) and the Swedish Research Council Formas suggest that maintaining or promoting appropriate tree cover in tropical African drylands may be crucial to improving deep soil and groundwater recharge under a future climate with more heavy rainfall.
In semi-arid West Africa, rainfall is characterized by a high spatial, intra‐ and inter‐annual variability. Annual rainfall is concentrated in a single, relatively short, rainy season that occurs between May and October. Rainfall intensities are high and a large proportion of annual rain falls during very intense storms.
In the same study area, the researchers found that there was an optimum tree cover that maximized groundwater recharge, which reflects the balance between the positive and negative effects of trees. The optimum tree cover represents a threshold below which increasing tree cover leads to improved groundwater recharge whereas above this threshold more trees result in reduced water yields. In water‐limited environments, understanding the potential thresholds in the relationship between tree cover and water availability is critical.
In a similar study in China’s semi-arid Loess Plateau, researchers have estimated the threshold at which additional revegetation in the area will cause a shortage in the water supply for human activities. Additionally, they found that this threshold could be significantly reduced in the future owing to climate change and increased water withdrawals and called for a better match of species and planting density in large‐scale restoration programs.
In line with the growing awareness of the important relationship between tree cover and groundwater recharge, more research is needed to better understand how this relationship will change in response to projected changes in rainfall intensity.