To this end, we used freely available satellite images from the European Copernicus Sentinel-2 mission and analyzed these via the mapme.vegetation tool. So-called vegetation indices such as the Normalized-Difference Vegetation Index (NDVI), can be calculated from the Sentinel-2 images and help to understand changes in vegetation cover better. Based on NDVI, we created maps that show the spatial and temporal dynamics of vegetation growth as a proxy for reduced soil erosion in an area encompassing about 100,000 hectares.
The Biji catchment is placed in a semi-arid region with about 450 mm of annual rainfall. Next to the satellite observation, we looked at digital precipitation data from the project Rainfall Estimates from Rain Gauge and Satellite Observations (CHIRPS). Based on this, we observed substantial precipitation anomalies for the years we were analyzing, with reduced rainfall at the beginning towards higher rainfall rates in later years (Figure 2). It is very likely that the growth of vegetation that we measured with the Sentinel-2 satellite observations depends on the amount of rainfall we observe in a given vegetation period, thus it is important to consider rainfall patterns.