Hydrological Regime In Loess Plateau And Its Ecological Effects Assessment Under Varying Conditions

Under the influence of climate change and land use change, runoff of medium and small basins in loess hilly area reduced greatly from the 1980 s, affecting the regional hydrological cycle and water balance and it limits the sustainable development of economy and society. This study selected a typical medium-sized basin- Qinghe River as a research object, and used the distributed hydrological model- SWAT model to simulate the runoff process for future regional water resources utilization and management, and environmental protection.Based on the daily meteorological data of seven weather stations surrounding the basin and the hydrological data between Jingcun Station to Zhangjiashan Station in Jinghe River in 1959 to 2010, as well as the land use data of 1990, 2000 and 2009, the paper analyzed the spatial and temporal changes of climate, land use, and runoff, then built SWAT model to simulate the impact of runoff and climate changes on environment. The results were as follows:(1)1981-2005, The annual variation of precipitation had a significant downward trend, the rainfall distribution during the year was uneven, mainly concentrated in the May to October, accounting for about 80% of the total annual precipitation. Interannual variability of the average annual temperature was intense. Based on simulation data of 1960 to 2010, we found that the runoff of flood season(from July to October) was more than 70% of the total’s. The main land use types of river were cropland, forest and grassland; 1990-2000, it had a significant increase in area of forest and area of grassland reduced; 2000-2009, the land-use changes were slight.(2)The paper built SWAT model and simulated surface runoff compared with estimate data, the Ens, R2 and Re of yearly runoff in 1975 to 1980 were 0.84, 0.95, 12.12%; In 1982 to 1985, the Ens, R2 and Re were 0.73, 0.89, 9.72%. The Ens, R2 and Re of monthly runoff in 1975 to 1980 were 0.94,0.96,5.05%; In 1982 to 1985, the Ens, R2 and Re were 0.90, 0.83, 7.12%. So we considered the SWAT model is applicable to the river runoff simulation.(3)Using the calibrated model to simulate changes in runoff under different land use conditions, the results showed that, the annual amount of evaporation continued to increase under different land use, runoff showed a significant downward trend. So that conceding the land to forestry could reduce runoff in semi-arid areas. In addition, the simulation results of three kinds of land use scenarios showed that grassland and forest would consume runoff, but the grassland was less than the woodland, so conceding the land to grassland was more conducive to maintaining the watershed runoff.(4)The climate and runoff change also were impact to watershed ecology. 1980-2014, the average temperature rised and rainfall reduced, annual NPP values fluctuated downward; NPP was positively correlated with watershed precipitation. The vegetation NDVI and annual runoff had opposite trend. This showed that, with the rise of NDVI, vegetation coverage increased and regional evapotranspiration increased, it would lead to a reduction of the runoff.