## 2 Materials and Methods  
### Study Area  
The study area covers the Horn of Africa (HoA), which includes Eritrea, Ethiopia, Djibouti, Somalia, and Kenya (Figure 1). The Horn of Africa is one of the highest populated regions of Africa, and the total population reaches about 165 million, of which Ethiopia is the most populous country. The region encompasses diversified mountains, high-lands, valleys, plains, and lowlands. The topography of the region descends from about 5200 meters above mean sea level at Mt. Kenya to about 126 meters below sea level in the Danakil Depression at the border area of Eritrea and Ethiopia (Figure 1).  
The climate of the Horn of Africa is characterized by warm arid in the coastal areas and lowlands of Somalia, Djibouti, and Eritrea, warm semi-arid in the lowlands of Ethiopia and Kenya, cool humid in the high mountains of Ethiopia and Kenya, warm, humid climate dominating highlands of Ethiopia and Kenya, while Western Kenya is hot and humid. The climate variability in the region is highly influenced by the movement of the Intertropical Convergence Zone (ITCZ), the effect of the Sahara Desert, especially in the northeastern parts, El Nino Southern Oscillation (ENSO), and the warm Indian Ocean currents and surface temperature changes [1; 26; 27]. Bimodal seasonal rainfall distributions characterize Horn of Africa [28]; according to 2001-2016 Tropical Rainfall Measuring Mission (TRMM) data, the mean annual precipitation ranges from 81 to 2130 mm in the lowlands per year in the highlands [29]. The main rainfall regimes and seasons of the Horn of Africa are wet from March to May, dry from June to August, wet from September to November, and dry from December to February, but there are obvious differences from southern Kenya to Eritrea with this seasonality.  
The land cover can be generalized from the satellite image extractions. The European Space Agency land use/land cover data (2015) of 300 m spatial resolution shows that the most dominant land covers are shrulbands, croplands (agriculture), forest areas, and grasslands representing 38.9%, 20.4%, 14.1%, and 12.6%, respectively (Figure 2a). Grasslands and shrulbands are dominant in southern parts of Ethiopia and Somalia, and northern parts of Kenya. Cropland land occupies large parts of the highland areas of Kenya, Ethiopia, and Eritrea. Agricultural activities, forests, and water bodies are more common in the western parts of the Horn of Africa and in the Rift Valley areas (Kenya et al., 2015). The most dominant agroecological zones in the Horn of Africa are of tropical climatic types which include warm arid, warm semi-arid, cool semi-humid, and cool semi-arid types covering 36.3%, 19.6%, 2.5%, and 1.2%, respectively (Figure 2b). The tropical warm arid zones are common in large parts of Somalia and Djibouti, western and eastern lowlands of Eritrea, and the eastern side of Kenya. Apart from the impact of climate change on terrestrial vegetation production and phenology, clearing forests and shrulbands for the agricultural purpose by farmers is a common practice in some countries of the region, and this has increased the pressure on the land and endangered ecosystem services (Kenya et al., 2015).  
Figure 1: The elevation range in the Horn of Africa (DEM source: SRTM) and the countries within.