Research On Responses Of Runoff To Land Use Changes In Yanwachuan Watershed In The Loess Tableland-Gully Region

In recent years, research on the responses of runoff to land use/land cover changes arouses a broad attention in hydrology and ecology. The loess tableland-gully region is located on the southern Loess Plateau, also the middle reaches of Yellow River, and is the most serious region of soil and water loss associated with its climate, vegetation, and soil characteristics. In order to understand the hydrology conditions and the responses of runoff to land use/land cover changes in the region, this paper used the distributed hydrological model SWAT (Soil and Water Assessment Tool) to simulate runoff and make adaptation assessments by taking Yanwachuan watershed, Gansu Province, as a study area. The runoff responses under different land use scenarios were then analyzed quantitatively.According to the SWAT model database building requirements, the data collected and processed were used to create the spatial database and non-spatial database. Then 23 sub-watersheds and 155 HRUs were automatically delineated by the DEM and stream networks in Yanwachuan watershed. Meteorological observation data were used to simulate runoff and hydrological observation data of 25 years in the watershed were used to calibrate and validate the model parameters and simulation results. Results show that in the calibration and validation periods by years, Nash-suttcliffe coefficients are 0.81 and 0.60 and relative coefficients are 0.95 and 0.88, respectively. In calibration and validation periods by mouths, Nash-suttcliffe coefficients are 0.88 and 0.87 and relative coefficients are 0.94 and 0.88, respectively. The result indicates that SWAT model can be successfully applied to the area.Based on the SWAT model validated, the runoff responses to different land uses were simulated. Results show that the runoff depth is increased after turning into cultivated land and reduced after turning into forest land and grass land. Results of annual runoff simulation show that runoff depth is increased by 11.93% after turning into cultivated land and reduced by 19.43% and 10.44% after turning into forest land and grass land, respectively. Results of monthly runoff simulation show that forest land and grass land reduce the flood peak significantly and cultivated land increases the flood peak on the contrast. From average monthly runoff depth in August, it is found that comparing to current land use, forest land is reduced by 24.59%, grass land is reduced by 12.28%, and cultivated land is increased by 15.42%. Forest land and grass land play important roles in conserving water and these patterns of land use can release water in dry season and regulate the annual runoff distribution.The quantitative analysis of runoff responses under different land uses/land covers may provide data and technical supports for local authorities in ecological construction.