Optimizing Satellite-Based Precipitation Estimation for Nowcasting of Rainfall and Flash Flood Events over the South African Domain

Estelle De Coning

doi:10.3390/rs5115702

Abstract

The South African Weather Service is mandated to issue warnings of hazardous weather events, including those related to heavy precipitation, in order to safeguard life and property. Flooding and flash flood events are common in South Africa. Frequent updates and real-time availability of precipitation data are crucial to support hydrometeorological warning services. Satellite rainfall estimation provides a very important data source for flash flood guidance systems as well as nowcasting of precipitation events for the data sparse regions of the African continent. Although low earth orbiting satellites with microwave instruments provide good quality rainfall estimates, their temporal and spatial resolution are not adequate for time-critical services. Precipitation estimation using geostationary satellites is less accurate, but provides excellent spatial coverage, is updated frequently and is available in real-time. This study compares different ways to use and combine satellite precipitation estimates and numerical weather prediction model fields over the South African domain in order to determine the optimal estimate of precipitation, which can also be applied in real-time to support flash flood guidance.

Highlights

Global measurements of precipitation are essential to the manage water resources and understand the global climate and hydrological cycle [1]
The aim of this study is to describe an improved methodology to combine the HE with the UMS in order to enhance the input to the South African Flash Flood Guidance system, especially along the coastlines where wintertime stratiform rainfall events are often not captured by the HE
It was found that monthly bias ratios for HE and UMS ranged from 0.125 to 8 in more than 90% of the grid boxes over the South African domain in all months except July (>80%), August (>50%) and September (Figure 4)

Summary

Introduction

Global measurements of precipitation are essential to the manage water resources and understand the global climate and hydrological cycle [1]. Rain gauges provide a relatively good direct measurement of rainfall at a specific point. The availability of rain gauge data at a sufficient spatial. Radar systems can provide a valuable indirect measurement of rainfall, this remotely sensed data source has limitations; its accuracy deteriorates with range from the radar and interference due to clutter, beam blockage and anomalous propagation have to be accounted for. The main advantages of satellite rainfall estimates are the high spatial resolution and coverage over regions where other sources of rainfall data are often not available (oceans, mountains, sparsely populated areas). Sensed rainfall derived from satellite data can provide valuable information for identifying hazardous situations, such as heavy rainfall, that could result in flash floods—even in areas without rain gauges and/or radar systems [3]

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Results

Conclusion