# Precipitation Products' Inter-Comparison over East and Southern Africa 1983-2017
## 1 Introduction  
The African continent is one of the most vulnerable places in the world; its population is over a billion people, most of whom live in semi-arid regions heavily prone to droughts, while other regions are plagued by floods. It is an economically and politically unstable continent, where most of the people live below the poverty threshold and social inequalities often make life precarious. African ecosystems are already being affected by climate change, and future impacts are expected to be substantial [1]. A reduction in precipitation is likely in Northern Africa and the southwestern parts of South Africa by the end of the 21 st century, whereas in regions of complex topography such as the Ethiopian Highlands, downscaled projections indicate likely increases in rainfall and extreme rainfall [1]. Climate change will amplify the existing stress on water availability, affecting agricultural production and food security. This scenario, characterized by a high dependence on agriculture and a lowcapacity to adapt to climate change, is expected to contribute to the exaggeration of social instability [2; 3]. In recent years, Africa has witnessed a series of extreme weather events that have affected the population ranging from extreme droughts to severe floods, highlighting the particular proneness of certain regions to such kind of events. In 2015 Southern Africa was hit by a very severe drought caused by the El Nino episode and intensified by climate change [4]. A strong drought episode during 2011 in Somalia caused the death of tens of thousands of people due to malnutrition and more than eleven million people in East Africa have faced severe food shortages [5]. Conversely, extreme rainfall gave rise to flood events in Ethiopia, Somalia, Kenya, and Uganda during the El Nino-related 1997-1998 episode, and widespread flash and river floods hit the region during the short rainy season in 2019. With this frame of reference, the relevant role played by precipitation estimates and forecasting at different time scales is clear. On the one hand, proper monitoring and short-time forecasting of precipitation are necessary in order to improve alert systems and damage reduction protocols. On the other hand, knowledge of the climatology of precipitation in terms of analysis of the past events, trends of extreme events, and variability in both can enhance awareness of issues connected to water resources and contribute, together with seasonal and decadal forecasting, to the improvement of water resource management, agricultural planning, and food security. Thus, precious information is contained in long-term datasets of accurate precipitation estimates over the past decades. Although the primary and direct sources of precipitation data come from rain gauges, they are often inadequate tools because of their uneven spatial distribution. This is particularly an issue in Africa, where the density of ground stations can be very scarce with an average station density of just one per 26,000 km\({}^{2}\), eight times lower than the World Meteorological Organization (WMO) minimum recommended level [6]. This problem is further aggravated by the high spatial variability of precipitation in many regions of Africa, making the data produced by a rain gauge representative only over a few kilometers' radius around the station [7]. Finally, the reliability of the data and continuity of station operations cannot be guaranteed due to associated maintenance costs [8]. These limitations have increased the importance of complementing the ground-based measurements with precipitation estimates based on satellite observations. Satellite products have the advantage of providing data sets with global spatial coverage and a long temporal extension, in some cases of more than 30 years [9; 10; 11].