Abstract
Rainfall during typhoons is one of the most important water resources in Taiwan, but heavy typhoon rainfall often leads to serious disasters and consequently results in loss of lives and property. Hence, accurate forecasts of typhoon rainfall are always required as important information for water resources management and rainfall-induced disaster warning system. In this study, a methodology is proposed for providing quantitative forecasts of 24 h cumulative rainfall during typhoons. Firstly, ensemble forecasts of typhoon rainfall are obtained from an ensemble numerical weather prediction (NWP) system. Then, an evolutionary algorithm, i.e., genetic algorithm (GA), is adopted to real-time decide the weights for optimally combining these ensemble forecasts. That is, the novelty of this proposed methodology is the effective integration of the NWP-based ensemble forecasts through an evolutionary algorithm-based strategy. An actual application is conducted to verify the forecasts resulting from the proposed methodology, namely NWP-based ensemble forecasts with a GA-based integration strategy. The results confirm that the forecasts from the proposed methodology are in good agreement with observations. Besides, the results from the GA-based strategy are more accurate as compared to those by simply averaging all ensemble forecasts. On average, the root mean square error decreases about 7%. In conclusion, more accurate typhoon rainfall forecasts are obtained by the proposed methodology, and they are expected to be useful for disaster warning system and water resources management during typhoons.
Highlights
Based on the report of the World Meteorological Organization [1], the tropical cyclone is the second ranked natural disaster in terms of loss of life
We focus on the assessment of Taiwan Typhoon and Flood Research Institute (TTFRI)-ensemble prediction system (EPS) members
The performance of the rainfall forecasts provided by all members in TTFRI-EPS is evaluated and typhoon Saola is taken as an example
Summary
Based on the report of the World Meteorological Organization [1], the tropical cyclone is the second ranked natural disaster in terms of loss of life. Statistically-based techniques fail to provide efficient forecasts of typhoon rainfall with a longer lead time. With the development of atmospheric science and computer technology, the use of numerical weather prediction (NWP) techniques for typhoon rainfall forecasting has been receiving considerable attention (e.g., [10,11,12,13,14]). In order to provide accurate rainfall forecasts when typhoons affect Taiwan, a NWP-based ensemble prediction system (EPS) is established by Taiwan Typhoon and Flood Research. For providing more accurate quantitative forecasts of 24 h cumulative rainfall during typhoons, a methodology based on the use of ensemble NWPs with a meta-heuristic-based integration strategy is proposed. Through the ensemble numerical weather prediction system in Taiwan (i.e., TTFRI-EPS), the NWP-based ensemble forecasts of typhoon rainfall are obtained.
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