Effects of Rainfall and Underlying Surface on Flood Recession-The Upper Huaihe River Basin Case

The effects of rainfall and underlying surface conditions on flood recession processes are a critical issue for flood risk reduction and water use in a region. In this article, we examined and clarified the issue in the upper Huaihe River Basin where flood disasters frequently occur. Data on 58 rainstorms and flooding events at eight watersheds during 2006-2015 were collected. An exponential equation (with a key flood recession coefficient) was used to fit the flood recession processes, and their correlations with six potential causal factors-decrease rate of rainfall intensity, distance from the storm center to the outlet of the basin, basin area, basin shape coefficient, basin average slope, and basin relief amplitude-were analyzed by the Spearman correlation test and the Kendall tau test. Our results show that 95% of the total flood recession events could be well fitted with the coefficient of determination (R-2) values higher than 0.75. When the decrease rate of rainfall intensity (Vi) is smaller than 0.2 mm/h(2), rainfall conditions more significantly control the flood recession process; when Vi is greater than 0.2 mm/h(2), underlying surface conditions dominate. The result of backward elimination shows that when Vi takes the values of 0.2-0.5 mm/h(2) and is greater than 0.5 mm/h(2), the flood recession process is primarily influenced by the basin's average slope and basin area, respectively. The other three factors, however, indicate weak effects in the study area.