Comparison of rainfall estimations by TRMM 3B42, MPEG and CFSR with ground-observed data for the Lake Tana basin in Ethiopia

A W Worqlul,S Langan,T S Steenhuis,A A Adem,S S Demissie,B Maathuis

doi:10.5194/hess-18-4871-2014

Abstract

Abstract. Planning for drought relief and floods in developing countries is greatly hampered by the lack of a sufficiently dense network of weather stations measuring precipitation. In this paper, we test the utility of three satellite products to augment the ground-based precipitation measurement to provide improved spatial estimates of rainfall. The three products are the Tropical Rainfall Measuring Mission (TRMM) product (3B42), Multi-Sensor Precipitation Estimate–Geostationary (MPEG) and the Climate Forecast System Reanalysis (CFSR). The accuracy of the three products is tested in the Lake Tana basin in Ethiopia, where 38 weather stations were available in 2010 with a full record of daily precipitation amounts. Daily gridded satellite-based rainfall estimates were compared to (1) point-observed ground rainfall and (2) areal rainfall in the major river sub-basins of Lake Tana. The result shows that the MPEG and CFSR satellites provided the most accurate rainfall estimates. On average, for 38 stations, 78 and 86% of the observed rainfall variation is explained by MPEG and CFSR data, respectively, while TRMM explained only 17% of the variation. Similarly, the areal comparison indicated a better performance for both MPEG and CFSR data in capturing the pattern and amount of rainfall. MPEG and CFSR also have a lower root mean square error (RMSE) compared to the TRMM 3B42 satellite rainfall. The bias indicated that TRMM 3B42 was, on average, unbiased, whereas MPEG consistently underestimated the observed rainfall. CFSR often produced large overestimates.

Highlights

Precipitation is a major component of the water cycle, and is responsible for depositing approximately 505 000 km3 of the fresh water on the planet (Ramakrishna and Nasreen, 2013)
The main rainy seasons were found to be significantly correlated with the El Niño–Southern Oscillation (ENSO; Camberlin, 1997), and most of the drought seasons in Ethiopia are more likely to occur during warm ENSO events (Seleshi and Demaree, 1995)
If we look at the rainfall distribution throughout the year, we found that the rainfall estimates of Multi-Sensor Precipitation Estimate–Geostationary (MPEG) and Climate Forecast System Reanalysis (CFSR) agree with the ground-based observation of 84 to 86 % of the annual rainfall that occurs in the rainy monsoon phase from June to September, as exemplified in Fig. 5 for Addis Zemen and Agre Genet stations

Summary

Introduction

Precipitation is a major component of the water cycle, and is responsible for depositing approximately 505 000 km (or on average 990 mm) of the fresh water on the planet (Ramakrishna and Nasreen, 2013). It is one of the major water balance components of the global water budget. The Rahad, Dindir and Welaka sub-basins in the Blue Nile basins, Ethiopia, each had only one rainfall station, despite a catchment area greater than 5000 km. The Rahad, Dindir and Welaka sub-basins in the Blue Nile basins, Ethiopia, each had only one rainfall station, despite a catchment area greater than 5000 km2 This situation is not likely to improve in the near future.

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Methods

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Discussion

Conclusion