# Precipitation Products' Inter-Comparison over East and Southern Africa 1983-2017
## 3 Regions of Study and Precipitation Climatology  
### East Africa  
The analyzed region extends from 5S to 20N and from 28E to 52E including Ethiopia, Djibouti, Eritrea, part of Sudan, South Sudan, Somalia, Kenya, Uganda, northern Tanzania, Rwanda, and Burundi (Figure 1). It is a geographically very complex region located on an area of friction between tectonic plates, and therefore mainly characterized by plateaus and mountain chains. The most important geological feature of the region is the presence of the Great Rift Valley extending for 5500 km from the Red Sea's junction with the Gulf of Aden, then southwest toward Kenya, and finally south to Mozambique. The oldest and best-defined rift, usually referred to as the Ethiopian Rift, is located in the Afar region covering part of Ethiopia, Eritrea, and Djibouti. Then it divides into two branches crossing the equator, the Eastern and Western Rifts, enclosing the large plateau where Lake Victoria lies. The Great Rift Valley is bordered by escarpments with altitudes varying from a few hundred to a few thousand meters, and is surrounded by highlands, the western and eastern Ethiopian Highlands and the East Africa Highlands. The complex geological processes that led to the formation of the Rift Valley are also responsible for the formation of several large lakes, including Lake Victoria, the largest lake in Africa and the second largest in the world. In this region we find the two highest mountains on the entire continent, Mount Kilimanjaro (5895 m) and Mount Kenya (5199 m). Another important geographical feature of EA is the presence of desert areas: the Chalbi desert north-east of Kenya, the Somali desert, the Dancali desert between Eritrea and northeastern Ethiopia, and the Sudan desert. As a result of the simultaneous presence of various regional factors, i.e., complex topography, maritime influence, and lakes, with large-scale tropical controls, a strong spatial variability characterizes EA's precipitation intensity and seasonality [42]. Precipitation varies from less than 50 to almost 2000 mm year\({}^{-1}\), as obtained by averaging the time series of the three products. The lowest values are found in the region of the Horn of Africa and Sudan, two mainly arid regions, whereas the highest values are located in the mountainous area of western Ethiopia, the area of the Lake Victoria, and the mountain chain of Rwenzori at the border between Uganda and the Democratic Republic of Congo. Likewise, the precipitation seasonality shows a high spatial variability as presented in Figure 2 for the monthly climatology from the average of the three precipitation products. A wide area including Somalia, Eritrea, northeastern Kenya and eastern Ethiopia is characterized by two precipitating seasons, the first one from March to May (the so-called _long rain season_) and the second one concentrated between October and December (the _short rain season_). The rain seasons are separated by dry periods (boreal summer and winter)during which the monthly precipitation is lower than 20 mm month-1. In the northern part of Sudan (north of 15N), mainly covered by desert, precipitation is always lower than 20 mm month-1, while central Sudan and South Sudan have a single precipitating season during the boreal summer (June-September) with more intense precipitation up to a maximum of 140 mm month-1. Precipitation is mainly concentrated in a single season in the western mountainous area of Ethiopia, the Ethiopian Highlands, lasting from June to September with precipitation peaks observed in July and exceeding 200 mm month-1. The south-western part of EA (Uganda and Tanzania) has a bimodal precipitation seasonality, from March to May and from October to December, with the more abundant precipitation concentrated in the area surrounding Lake Victoria, where unlike the rest of EA significant precipitation occurs also during January and February.