Links between land cover change and climate in the Horn of Africa

Land use and land cover change significantly influence regional energy budgets, and hydrological and biogeochemical cycles which may occur from both anthropogenic and natural disturbances. Likewise, vegetation may also respond dynamically to climate. In the past decades, the Horn of Africa has been hit by several droughts and heatwaves causing severe economic, environmental, and social damage. To evaluate and mitigate such impacts, it is necessary to establish and quantify the linkage between land cover change and regional climate. This study presents an observational analysis of recent (2001–2019) historical changes in land cover and land use and their relation to climate in the Horn of Africa. 

Firstly, we evaluate changes in land cover using the Moderate Resolution Imaging Spectrometer (MODIS) dataset. Results indicate steady expansion of grasslands (net gain is 1.2% of total area) and an opposite pattern for open shrublands during the period 2001–2016. Importantly, deforestation of evergreen broadleaf forest (0.3% of the total area) is also noticeable in continuous fractional vegetation cover (FVC) analysis. Next, the Global Database of Historical Yields (GDHY) is explored to identify the yield trends for two main cereals: maize and wheat.  Wheat yield shows increasing trends in the northern and southern parts, while maize yields increase in Ethiopia and mildly decrease in Kenya. To quantify the adverse impact of drought on yields, three drought indices are used: (a) Standardized Precipitation Evapotranspiration Index (SPEI), (b) self-calibrating Palmer Drought Severity Index (scPDSI), and (c) Standard Evapotranspiration Deficit Index (SEDI). The analysis identifies SPEI12 as arguably the best performing drought index for monitoring and forecasting impacts on yields in this region. 

Finally, a Conditional Spectral Granger Causality (CSGC) algorithm is employed for understanding the influence of climate variability on vegetation dynamics. Although the influence of climatic factors (i.e., precipitation, temperature, and solar energy radiation) on vegetation dynamics is heterogeneous, given the wide spectrum of climate regimes in the region, an overall increased influence of temperature on vegetation dynamics is revealed. In conclusion, the observational evidence indicates that climate plays an important role as a driver of both crop and natural vegetation change in the Horn of Africa.