Study on streamflow response to land use change over the upper reaches of Zhanghe Reservoir in the Yangtze River basin

The Zhanghe Reservoir in Yangtze River basin plays a key role in fulfilling the crop water requirements of the irrigation area in its downstream region. This study employs the SWAT (Soil and Water Assessment Tool) model to simulate the variations of Zhanghe Reservoir inflow. The model performed well at monthly timescale, with the values of both NSE and R-2 above 0.7. The land use distribution and the structure changes in 1990, 2000, and 2015 are employed to study the reservoir inflow responses to the land use changes in the contributed basin area. In the historical period (1990-2000), the streamflow was decreased by 0.4%, accompanied by the reductions of farmland and grassland area, and the increase of forestry area. The land use scenarios are further designed for considering possible future land use alterations. The low flow responses to the completely forestry cover for the basin is more obvious to the completely grassland cover. Accordingly, the further afforestation may aggravate the drought situation due to the low flow reduction. In addition, the high flow responses are reversed to these two land cover situations. The obtained results are useful for designing future sustainable development strategies for the region.