Impacts of land use change and climate variability on hydrology in an agricultural catchment on the Loess Plateau of China

Land use and climate are two main factors directly influencing catchment hydrology, and separation of their effects is of great importance for land use planning and water resources management. Using the SWAT (Soil and Water Assessment Tools) model, we assessed the impacts of land use change and climate variability on surface hydrology (runoff, soil water and evapotranspiration) in an agricultural catchment on the Loess Plateau of China. Results indicated that SWAT proved to be a powerful tool to simulate the effect of environmental change on surface hydrology. The Nash–Sutcliffe model efficiency (Ens), Percent bias (PBIAS) and ratio of root mean square error to measured standard deviation (RSR) for annual flow was 0.87, 4.0%, 0.36 during calibration period and 0.87, 2.5%, 0.36 during validation periods, respectively. During 1981–2000, about 4.5% of the catchment area was changed mainly from shrubland and sparse woodland to medium and high grassland, and climate changed to warmer and drier. The integrated effects of the land use change and climate variability decreased runoff, soil water contents and evapotranspiration. Both land use change and climate variability decreased runoff by 9.6% and 95.8%, respectively, and decreased soil water contents by 18.8% and 77.1%. Land use change increased evapotranspiration by 8.0% while climate variability decreased it by 103.0%. The climate variability influenced the surface hydrology more significantly than the land use change in the Heihe catchment during 1981–2000; therefore, the influence of climate variability should be considered and assessed separately when quantifying the hydrological effect of vegetation restoration in the Loess Plateau.