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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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Atmos. Meas. Tech., 10, 2009-2019, 2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
06 Jun 2017
Satellite-based high-resolution mapping of rainfall over southern Africa
Hanna Meyer1, Johannes Drönner2, and Thomas Nauss1 1Environmental Informatics, Faculty of Geography, Philipps-University Marburg, Deutschhausstr. 10, 35037 Marburg, Germany
2Database Research Group, Faculty of Mathematics and Informatics, Philipps-University Marburg, Hans-Meerwein-Str. 6, 35032 Marburg, Germany
Abstract. A spatially explicit mapping of rainfall is necessary for southern Africa for eco-climatological studies or nowcasting but accurate estimates are still a challenging task. This study presents a method to estimate hourly rainfall based on data from the Meteosat Second Generation (MSG) Spinning Enhanced Visible and Infrared Imager (SEVIRI). Rainfall measurements from about 350 weather stations from 2010–2014 served as ground truth for calibration and validation. SEVIRI and weather station data were used to train neural networks that allowed the estimation of rainfall area and rainfall quantities over all times of the day. The results revealed that 60 % of recorded rainfall events were correctly classified by the model (probability of detection, POD). However, the false alarm ratio (FAR) was high (0.80), leading to a Heidke skill score (HSS) of 0.18. Estimated hourly rainfall quantities were estimated with an average hourly correlation of ρ = 0. 33 and a root mean square error (RMSE) of 0.72. The correlation increased with temporal aggregation to 0.52 (daily), 0.67 (weekly) and 0.71 (monthly). The main weakness was the overestimation of rainfall events. The model results were compared to the Integrated Multi-satellitE Retrievals for GPM (IMERG) of the Global Precipitation Measurement (GPM) mission. Despite being a comparably simple approach, the presented MSG-based rainfall retrieval outperformed GPM IMERG in terms of rainfall area detection: GPM IMERG had a considerably lower POD. The HSS was not significantly different compared to the MSG-based retrieval due to a lower FAR of GPM IMERG. There were no further significant differences between the MSG-based retrieval and GPM IMERG in terms of correlation with the observed rainfall quantities. The MSG-based retrieval, however, provides rainfall in a higher spatial resolution. Though estimating rainfall from satellite data remains challenging, especially at high temporal resolutions, this study showed promising results towards improved spatio-temporal estimates of rainfall over southern Africa.

Citation: Meyer, H., Drönner, J., and Nauss, T.: Satellite-based high-resolution mapping of rainfall over southern Africa, Atmos. Meas. Tech., 10, 2009-2019,, 2017.
Publications Copernicus
Short summary
A spatially explicit mapping of rainfall is required for southern Africa but obtaining accurate estimates is still a challenging task. We estimated hourly rainfall based on optical satellite data and neural networks. The results indicated that the majority of rainfall events could be captured by the model, but with a clear tendency to overestimate rainfall. Despite being a comparably simple approach, the presented rainfall retrieval could outperform a complex global rainfall product.
A spatially explicit mapping of rainfall is required for southern Africa but obtaining accurate...