Runoff simulation by SWAT model using high-resolution gridded precipitation in the upper Heihe River Basin, Northeastern Tibetan Plateau

Abstract. Precipitation stations are usually scarce and unevenly distributed in inland river basins, which restrict the application of the distributed hydrological model and spatial analysis of water balance component characteristics. This study regards the upper Heihe River Basin as a case, and daily gridded precipitation data with 3 km resolutions based on the spatial interpolation of gauged stations and the regional climate model is used to construct the soil and water assessment tool (SWAT). This study aims to validate the superiority of high-resolution gridded precipitation for hydrological simulation in data scarce regions. A scale transformation method is proposed by building virtual stations and calculating the lapse rate to overcome the defects of the SWAT model using traditional precipitation station data. The gridded precipitation is upscale from the grid to the sub-basin scale and results in accurate representation of sub-basin precipitation input data. A satisfactory runoff simulation is achieved, and the spatial variability of the water balance components is analysed. Results show that the precipitation lapse rate ranges from 40 mm/km to 235 mm/km and decreases from the southeastern to the northwestern areas; its changes trend is consistent with precipitation. The SWAT model achieves monthly runoff simulation compared with gauged runoff from 2000 to 2014; the determination coefficients are higher than 0.71, the Nash–Sutcliffe efficiencies are higher than 0.76 and the percent bias are controlled within ±15 %. The meadow and sparse vegetation are the major water yield landscapes, and the elevation band at 3,500 m to 4,500 m is the major water yield area in this basin. Precipitation and evapotranspiration presented a slightly increasing trend, whereas water yield and soil water content presented a slightly decreasing trend. This finding indicates that the high-resolution gridded precipitation data well depicts its spatial heterogeneity, and scale transformation significantly promotes the application of the distributed hydrological model in inland river basins. The spatial variability of water balance components can be quantified to provide references for the integrated assessment and management of basin water resources in data scarce regions.