Abstract
The spatio-temporal characteristic of rainfall in the Beles Basin of Ethiopia is poorly understood, mainly due to lack of data. With recent advances in remote sensing, satellite derived rainfall products have become alternative sources of rainfall data for such poorly gauged areas. The objectives of this study were: (i) to evaluate a multi-source rainfall product (Climate Hazards Group Infrared Precipitation with Stations: CHIRPS) for the Beles Basin using gauge measurements and (ii) to assess the spatial and temporal variability of rainfall across the basin using validated CHIRPS data for the period 1981–2017. Categorical and continuous validation statistics were used to evaluate the performance, and time-space variability of rainfall was analyzed using GIS operations and statistical methods. Results showed a slight overestimation of rainfall occurrence by CHIRPS for the lowland region and underestimation for the highland region. CHIRPS underestimated the proportion of light daily rainfall events and overestimated the proportion of high intensity daily rainfall events. CHIRPS rainfall amount estimates were better in highland regions than in lowland regions, and became more accurate as the duration of the integration time increases from days to months. The annual spatio-temporal analysis result using CHIRPS revealed: a mean annual rainfall of the basin is 1490 mm (1050–2090 mm), a 50 mm increase of mean annual rainfall per 100 m elevation rise, periodical and persistent drought occurrence every 8 to 10 years, a significant increasing trend of rainfall (~5 mm year−1), high rainfall variability observed at the lowland and drier parts of the basin and high coefficient of variation of monthly rainfall in March and April (revealing occurrence of bimodal rainfall characteristics). This study shows that the performance of CHIRPS product can vary spatially within a small basin level, and CHIRPS can help for better decision making in poorly gauged areas by giving an option to understand the space-time variability of rainfall characteristics.
Highlights
Developing countries, including Ethiopia with rapid population growth, depend on rainfed agriculture, which is highly vulnerable to fluctuations in rainfall amount
The second part contains the analysis of spatio-temporal variability of rainfall within the basin using the Climate Hazards Group InfraRed Precipitation with Stations (CHIRPS) satellite rainfall estimates
Previous studies in the region [8,14,23,24,30,32,58], which consider the whole of our study area, the Beles Basin, as a lowland, showed that satellite rainfall estimates are better over the lowlands than over the highlands; our study demonstrates that at the local level within the Beles Basin, CHIRPS better estimated rainfall at highland regions than lowlands
Summary
Developing countries, including Ethiopia with rapid population growth, depend on rainfed agriculture, which is highly vulnerable to fluctuations in rainfall amount. In developing countries, observations of rainfall measurements from traditional ground weather stations are characterized by sparse, uneven distribution, poor data quality, temporally inconsistent and unable to access the data in time [8,9,10] Those problems are more common in inaccessible and rugged areas [11] such as the highlands of Ethiopia, where rainfall is extremely variable over short distances [12,13]. Analysis using point-based rain gauge observations is limited to the given particular location, which provides a poor estimation of spatial distribution of rainfall for areas such as Ethiopia, where rainfall is extremely variable over short distances To overcome these limitations, the recently developed long-term and spatially distributed satellite-based rainfall estimates have become important sources of rainfall data to analyze the spatial and temporal variability of rainfall, especially for data-sparse regions [8,16,17]
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