South African Weather Service operational satellite based precipitation estimation technique: applications and improvements

E De Coning,E Poolman

doi:10.5194/hess-15-1131-2011

Abstract

Abstract. Extreme weather related to heavy or more frequent precipitation events seem to be a likely possibility for the future of our planet. While precipitation measurements can be done by means of rain gauges, the obvious disadvantages of point measurements are driving meteorologists towards remotely sensed precipitation methods. In South Africa more sophisticated and expensive nowcasting technology such as radar and lightning networks are available, supported by a fairly dense rain gauge network of about 1500 daily gauges. In the rest of southern Africa rainfall measurements are more difficult to obtain. The local version of the Unified Model and the Meteosat Second Generation satellite data are ideal components of precipitation estimation in data sparse regions such as Africa. In South Africa hourly accumulations of the Hydroestimator (originally from NOAA/NESDIS) are currently used as a satellite based precipitation estimator for the South African Flash Flood Guidance system, especially in regions which are not covered by radar. In this study the Hydroestimator and the stratiform rainfall field from the Unified Model are both bias corrected and then combined into a new precipitation field. The new product was tested over a two year period and provides a more accurate and comprehensive input to the Flash Flood Guidance systems in the data sparse southern Africa. Future work will include updating the period over which bias corrections were calculated.

Highlights

There is mounting evidence that changes in the earth’s climate system will result in more frequent extreme weather events and an increased likelihood of temperature extremes, heat waves, and heavy precipitation events (IPCC, 2007)
The expectation is that the COMB should be slightly better in summer months, due to the bias correction applied to the HE
The quality of satellite based precipitation estimations for South and southern Africa are crucial to ensure the accuracy of flood and/or flash flood warnings

Summary

Introduction

There is mounting evidence that changes in the earth’s climate system will result in more frequent extreme weather events and an increased likelihood of temperature extremes, heat waves, and heavy precipitation events (IPCC, 2007). The World Meteorological Organisation (WMO) organized a series of sub-regional demonstration projects to improve severe weather forecast services in countries where sophisticated remote sensing forecast systems are not currently used (mostly developing countries). Such a project is currently running from South Africa and is called the Severe Weather Forecast Demonstration Project (SWFDP). The goals of this project include: improvement of the lead time of warnings, improved communication between global, regional and National Meteorological Centres (NMC), improved interaction of NMC with disaster management authorities before and during severe weather events (Poolman et al, 2008). One of the gaps identified in the project was that whereas the SWFDP succeeded in improving forecasting systems in the developing countries, there is a serious lack of nowcasting systems, for severe convective storms

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