Quantitatively Evaluate The Effects Of Precipitation And Vegetation Variation To Flood Under The Condition Of Single Rainstorm

Precipitation and vegetation are two key factors affecting floods in the watershed.Quantitative evaluating their contribution to flood is of great scientific significance to vegetation construction and water resources management.Based on the geographic information data and hydrometeorological data from 1983 to 2017 in red soil region of South China,we used cumulative anomaly method to divide time periods,and analyzed the characteristics of rainstorm and flood by linear regression method,moving average method and Mann-Kendall test method.Then the HEC-HMS model was used to simulate single rainstorm,and the contribution rates of precipitation and vegetation variation to total flood volume and peak flow were quantitatively calculated.The results showed that:(1)The runoff coefficient of rainstorm flood for 1983-2017 abruptly changed in 2003,thereby dividing the study period into baseline period and change period,namely 1983-2003 and 2004-2017.(2)The rainstorm volume and the total flood volume showed a non-significant upward trend in 1983-2017,1983-2003 and 2004-2017,and the future changes of both were persistent and would show an upward trend,but the duration was only eight years.The periodic variation characteristics of the rainstorm volume and the total flood volume found by the wavelet analysis real part contour map and the model square contour map were basically the same.The first,second and third main periods of rainstorm volume variation were 26 a,11a and 6a,respectively,while the change of total flood volume were mainly controlled by the two main periods of 10 a and 6a.The correlation coefficients(r)of total flood volume and rainstorm volume,peak flow and rainstorm volume,flood duration and rainstorm duration were 0.858,0.64 and 0.704,respectively,showing extremely significant correlation.While the correlation between precipitation intensity and total flood volume,peak flow were relatively low.It indicates that the rainstorm volume is closely related to the total flood volume,and the peak flow may be affected by vegetation coverage and other factors in addition to precipitation.(3)HEC-HMS model had good simulation effect on single rainstorm flood,with the evaluation results being within the error range.The contribution rates of precipitation and vegetation variation of different rainstorm floods were different with respect to the total flood volume or to the peak flow.The average contribution rate of precipitation and vegetation variation to the total flood volume was 66.5% and 33.5%,while to the peak flow was 58.9%and 41.1%,respectively.The average contribution rate of vegetation variation to peak flow is higher than that of total flood volume.(4)Under the condition of single rainstorm,the average contribution rates of precipitation and vegetation variation to the total flood volume and peak flow of unimodal flood were 53.4 %,46.6 % and 47.2 %,52.8 %,respectively,while the average contribution rates of multimodal flood were 65.4 %,34.6 % and 54.2 %,45.8 %,respectively.And the vegetation variation has a greater impact on unimodal flood.