Impacts of Changing Land Use and Land Cover on Regional Climate in Sub-Saharan Africa

Sub-Saharan Africa is a dynamic system in which human activity, ecosystems, and the atmosphere are tightly coupled. Changes in land use and land cover (LULC) driven by human activities are expected to continue across the continent over the coming decades. Rates of change vary depending on local biophysical conditions, demand for forest products like timber and woodfuels, as well as expansion of crop cultivation and grazing land, driven by growing domestic, regional, and global markets. Whereas past changes and future pathways of LULC have been the subject of multiple studies, few have focused on understanding land–atmosphere interactions. The tight coupling of land surfaces to the atmosphere in Sub-Saharan Africa may result in regional changes in climate that could be enhanced or negated by global climate change, and ultimately affect populations and ecosystems in climate-sensitive regions. Some evidence suggests that severe droughts in this region, which threaten livelihoods and are associated with increased conflict, may be linked to LULC changes, and thus understanding the impact of LULC changes on the regional climate is of great importance to local policy makers.

In this work the Weather Research and Forecasting model (WRF) is used to explore the impact that recent changes in LULC have had on the current climate of Sub-Saharan Africa. Initial investigations revealed that several of the land surface models in WRF were found to lack appropriate representations of surface albedo and leaf area index leading to errors in climate responses to LULCC. In order to overcome these issues, the CLM land surface model in WRF has been modified to prescribe satellite derived monthly leaf area index values for 17 bioclimate regions in Sub-Saharan Africa and the albedo values for sandy soils have been scaled up to bring the albedo of arid regions in better agreement with satellite estimates.

Two 17-year WRF simulations are forced by yearly-varying global reanalysis fields – one using LULC specific for each year and one using static LULC representative of the year 2001– to see the influence of LULC changes. LULC changes are processed/simulated using the Dinamica EGO framework. Within Dinamica EGO, observed LULC changes from the Moderate Resolution Spectroradiometer (MODIS) land cover MCD12Q1 product between 2001 and 2007 are compared by means of conditional probabilities (i.e. weights of evidence) against various spatial proximal explanatory variables such as population density, distance to the road network, elevation, among others. The resulting map depicts the probability that a grid cell within the domain will shift from one LULC class to another. By integrating the amount of change from the calibration period with the probability map, new simulated LULC maps are produced, and compared against observed maps for validation purposes.

Preliminary results indicate that changes in LULC between the years 2001 and 2017 can impact thermally driven atmospheric circulations in southern Africa, while the majority of Sub-Saharan Africa experiences only localized changes in climate where LULCC has taken place. Many of these localized changes include warming and drying in response to deforestation. More details on the impacts of LULCC including statistical significance of the LULCC driven climate impacts and interactions with the El Niño Southern Oscillation will be presented.