Assessing the spatio-temporal variability of vegetation productivity in Africa: quantifying the relative roles of climate variability and human activities

Quantitative attribution at the individual pixel level of the relative contributions of climate variability and human activities to vegetation productivity dynamics across Africa is generally lacking. This is because of the difficulty in establishing a baseline or potential vegetation against which the relative impacts of these factors can be assessed. This study addresses these gaps. First, annual potential net primary productivity (NPPP) for 2000-2014 was estimated for Africa using a model constructed from samples of NPP and environmental covariates from protected areas. Second, trends in NPPP, actual NPP (NPPA), and human-appropriated NPP (NPPH=NPPP - NPPA) were estimated and used in quantifying the relative contributions of climate and human activities to NPP dynamics. Over 2000-2014, NPP improvement was largely concentrated in equatorial and northern Africa, while subequatorial Africa exhibited the most NPP decline. Parts of Mali, Burkina Faso, and the central Africa region are associated with the greatest influence of climate-driven NPP improvement. Areas where humans dominated NPP decline include parts of Ethiopia and South Africa. Climate had a stronger role in driving NPP decline in subequatorial Africa. Nonetheless, further work is required to validate the results of this study with high-resolution imagery and field information.