Local biophysical impacts of idealized land-cover and land management changes on climate extremes in the semi-arid West African Savannas

The West African savannas region is currently undergoing extensive agricultural intensification due to rapid population growth. Those anthropogenic land cover changes (LCC) can have significant impacts at regional and seasonal scales but also on extreme weather events to which human, natural and economical systems are highly vulnerable. However, the effects of LCC on extreme events remain either largely unexplored at regional/local scale and/or without consensus. To address this issue, we investigate the biophysical impacts of idealized land use and land management changes (LCLMCs) scenarios on climate extremes in the semi-arid West African Savannas region. This analysis is conducted using high-resolution land-cover change experiments (at 3 km) covering the period from 2011 to 2023. These experiments utilize the fully coupled WRF-Hydro system, which incorporates surface and subsurface lateral flow while describing the vegetation dynamically. The local effects of idealized LCLMCs scenarios are derived through a comparison of multiple land-use and afforestation scenario-based simulations, reflecting a specific LCC transition, occurring over the Sudan Savanna of Burkina Faso and Ghana.

Analyzing 20 extreme weather indices, we find, on average, that LCC robustly lessens regional extreme rainfall by 8% for the number of wet days (R1mm) and by 7% for the heavy rainfall (R10mm) more than mean rainfall conditions (up to 2 times more). LCC can impact regional rainfall extremes 4 times more than temperature extremes on average and intensifies dry days. Afforestation options, such as the conversion of grassland to evergreen broadleaf forest or evergreen needleleaf forest, tend to mitigate the biophysical LCC-induced warming effect and lower the associated occurrence of temperature extreme events. Conversely, opposite effects can be observed under savannas-based afforestation options, likely due to their associated large sensible heat fluxes compared to grassland and cropland. The study investigates the underlying biophysical drivers behind these opposing effects.

We stress here that fully coupled modeling frameworks incorporating all aspects of land-use change and local positive feedback between the terrestrial hydrological system and the overlying atmosphere are needed to better evaluate land-based mitigation and adaptation strategies.