An intercomparison of 10-day satellite precipitation products during West African monsoon

Abstract

In the frame of the African Monsoon Multidisciplinary Analyses (AMMA) programme, a specific rainfall algorithm (EPSAT-SG; Estimation of Precipitation by SATellites – Second Generation) was developed for the requirements of the scientific community and an intercomparison exercise was undertaken to assess the performance of various rainfall analyses to help users of satellite precipitation estimates to take into consideration the limitations of these products. The intercomparison exercise presented in this article includes three regional precipitation products as well as seven operational global products that are publicly available and easily accessible on websites. This study has been performed using validation data from rain gauge observations analyses on the Sahelian region provided by the AGRHYMET centre, for three rainy seasons from 2004 to 2006. The 10 different satellite-based precipitation products are verified against the same reference ground-based dataset of 10-day rainfall accumulations at the 0.5° × 0.5° latitude–longitude resolution.

The performance of the different precipitation algorithms is assessed according to various indicators such as the behaviour of the precipitation distributions, several statistical parameters and spatial distribution of the errors. All the statistical results indicate that the three ‘near-real-time’ products (3B42-RT, CPC MORPHing technique (CMORPH) and Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks (PERSIANN)) have a poorer performance than the other products considered for intercomparison. In fact these algorithms cannot make use of useful inputs such as rain gauge observations that are not available at near real time. It is noted that the simple basic Geostationary Operational Environmental Satellite (GOES) Precipitation Index (GPI) product performs better, with a higher skill score index. The three products Global Precipitation Climatology Project (GPCP)-1dd, Global Satellite Mapping of Precipitation (GSMaP)-MVK and Tropical Rainfall Measuring Mission (TRMM)-3B42 obtain better statistical results but the best results are obtained by the precipitation products created specifically for this African region. The EPSAT-SG product has the best performance according to several statistical criteria including skill score, coefficient of determination and root mean square (RMS) error whereas the Rain Fall Estimation (RFE)-2.0 estimates offer the best match with validation estimates in term of distribution and bias. The Tropical Applications of Meteorology using SATellite and other data (TAMSAT) estimates have also similar statistically good results.

Acknowledgements

We thank the AGRHYMET centre and the affiliated African Meteorological Services for providing us with the gridded fields of 10-day precipitation used as validation dataset for this study and in particular Dr. Abdou Ali. Our thanks naturally extend to the authors of the various products compared in this article for making their product available on their web sites. We also thank Dr. Michel Desbois for having initiated this work.

Based on a French initiative, AMMA was built by an international scientific group and is currently funded by a large number of agencies, especially from France, the United Kingdom, the United States of America and Africa. It has been the beneficiary of a major financial contribution from the European Community's Sixth Framework Research Programme. Detailed information on scientific coordination and funding is available on the AMMA International web site: http://www.amma-international.org.