Quantifying the Effects of Land Surface Change on Annual Runoff Considering Precipitation Variability by SWAT

Runoff variations were influenced by climate variability and land surface change, but the mechanism was not clear, and quantification of their effects was not mature. To find a reliable method, we selected four sub-watersheds in Luanhe watershed in which runoff series had significant downward trends. We first calibrated and validated the Soil and Water Assessment Tool (SWAT) hydrological model by using the hydrometeorological data in reference period in the four sub-watersheds. The simulated runoff series agreed well with the observed ones, which demonstrated the model performed well. Then we reconstructed the runoff series in impaired period under 1970 and 2000 land use conditions without check dams. According to the simulation results, the contributions of precipitation variability, land use change and construction of large number of check dams were quantified by traditional method. It was found that precipitation variability was the main cause of runoff decrease. In this study, we proposed a new perception for distinguishing the contributions of land surface change and precipitation variability, and got different results from traditional method. Precipitation variability was the main factor for runoff decrease in Luanhe and Wuliehe sub-watersheds, and land surface change contributed more in Yixunhe and Liuhe sub-watersheds. The combined effects were not the summation of single effect of precipitation variability and land surface change. It is of great necessity to do further research on this issue, and will provide reliable information for water resources managers.