The Study Of Flood Forecasting Coupled With Ensemble Rainfall Forecast

Flood forecasting coupled with precipitation forecast information can prolong forecast period, thus winning precious time for making decisions of flood control operation. However, flood forecasting based on the results of "single" precipitation forecast has the uncertainty, which results from the uncertainty of precipitation forecast information. Decisions based on the above information with uncertainty may not be the best or even larger deviations may occur. For above problems, this paper took the basin above Huanren reservoir as a test basin, testing and evaluating ensemble forecast data of the four centers:UKMO, ECMWF, NCEP and CMC. Availability was researched whether the four centers’data can be used in flood forecasting and ensemble precipitation forecast of ECMWF was adopted to drive the Xinanjiang model for flood forecasting research. Main research contents and conclusions are as follows:(1)The ensemble forecast systems of the four centers were tested and evaluated by using TS score, BS score and Talagrand distribution. Results showed that each of the four ensemble forecasts had a certain prediction technique and the effects were equivalent. Talagrand distribution tests showed that the divergence of ensemble forecast of each center was not enough. Small-level precipitation predictions were bigger and large-level (such as heavy rain events) were smaller. In this test, UKMO and CMC Talagrand distributions were relatively better.(2)Based on statistical analysis of error characteristic values (accuracy rate, vacancy rate and missing rate) of ensemble average precipitation forecast of the four centers, feasibility analysis was taken for their applications in flood forecasting. The results showed that the accuracy of no rain forecast and light rain forecast were higher. Moreover, three estimation methods (bi-linear interpolation, inverse distance weighting method and the correlation coefficient method) were compared and the results showed that there was no absolutely optimal way. So integration of bi-linear interpolation method and inverse distance weighting was put forward for hydrometeorological coupling research.(3)According to basin characteristics above Huanren reservoir, Xinanjiang Model (3Components) was chosen as the flood forecast model and genetic algorithm was applied for parameter optimization.(4)Ensemble precipitation forecast were respectively applied to simulating flood process. And ensemble precipitation forecast had the advantage since it can get the range of runoff simulation, which can provide more useful risk information for decision makers. According to the characteristics of ensemble average precipitation forecast, the average precipitation data were revised and then adopted to simulating the flood process, resulting in a significant improvement of the effect.