Flood Response To Land-use And Land-cover Change In The Xixi Watershed Of Jinjiang River

The study area, Xixi watershed, is a sub-basin of Jinjiang Basin, located in Fujian Provice, southeastern part of China. Jinjiang Basin is one of the most developed zones in China. Since the late 20th century, the frequency of flood disaster has been higher than any time before. The watershed area is 1259 km2. The storm event was described as having a high intensity and short duration, contributing a significant quantity of precipitation in the study region. The region has a typical subtropical monsoon climate. The average annual temperature is 20.4℃with minimum and maximum temperatures occurring in January and July, respectively. The economy has developed quickly and the population density is increasing unceasingly. Land use and cover change of Xixi watershed is seriously. And thus the study concerning the impact of land use and cover changes on flood becomes significant in the region.In this study, a spatially distributed hydrologic model, HEC-HMS, was examined for its applicability in the Xixi watershed. The Soil Conservation Service (SCS) Curve Number method, the SCS Unit Hydrograph method and the Exponential Recession method were selected for the runoff volume computation, direction runoff computation and base flow computation, respectively. The Muskingum method was applied to flow routing. Eight storm records were used for model calibration and validation. To study the effect of time step length on the model results, simulations were performed for time step lengths ranging from 60min to 15min at the basin scale. The results indicated:For different time step length, the simulation results will be similar with changing the model parameters. For example, the travel time of the flood wave through routing reach (K) will increase with time step length decreases. A choice for a certain time step length should be made before calibration of the model, and a smaller time step length should, in principle, give a, more reliable result. To study the influence of forest cover changes on single-peaked and multiple-peaked storm runoff process. The analyses show that, along with the increase of forest coverage, the scenarios result in obvious decrease in peak discharge and volumes, and the sensitivity of hydrologic response to land use change tends to decrease as the frequency of the flood events increase. Furthermore, the influence of forest cover change on storm runoff, presented weakened with the rainfall intensity enhanced.