Analysis of streamflow responses to climate variability and land use change in the Loess Plateau region of China

- SWAT model was used to simulate monthly streamflow in the upper Sang-kan river basin.
- Recent perennial drought in the Sang-kan river was mainly induced by human activities.
- Land use change led to streamflow increase in the USK basin during 1986-2012.
- Change of climatic variability caused the streamflow to decline during 1986-2012.

Reduced streamflow is a major concern in the Haihe river basin, which supplies water for agriculture, industry and the growing population along the river. The upper Sang-kan (USK) river basin is the headwater of the Haihe river. To understand the drivers of streamflow change in this basin, effects of land use change and climate variability on temporal flow variability were studied using the Soil and Water Assessment Tool (SWAT). The calibration and validation results of the Scenario 0 (S0) model (with land use of 1986 and climate derived from 1979 to 1990) indicated that SWAT simulated monthly streamflow well. This was indicated by the Nash-Sutcliffe model efficiency (NS) and the Coefficient of Correlation (r2) for monthly flow, which were 0.89 and 0.91 for the calibration period (1981-1985) and 0.79 and 0.82 for the validation period (1986-1990), respectively. After calibration and validation of the SWAT model (S0), three different scenarios were simulated and compared in order to study the effects: Scenario 1 (land use of 2000 and climate during the 1979-1990 period, abbreviated as S1), Scenario 2 (land use of 2012 and climate during the 1979-1990 period, abbreviated as S2), and Scenario 3 (land use of 2012 and climate during the 2001-2012 period, abbreviated as S3). By comparing the simulated hydrological results of S0 vs. S1 and S2, and S2 vs. S3, and the annual changes in water use, it can be concluded that the recent perennial drought in the USK river has mainly been caused by human activities; warmer temperatures and less rainfall resulted in streamflow declining by 39.1%, while land use changes and the accompanied water use change for irrigation resulted in surface runoff increasing by 37.6% and streamflow increase between 2.2% and 3.9%, during the period of 1986-2012; increasing ground water and surface water usage for urbanization, industrialization, and reservoir constructions can be attributed from 63.1% to 64.8% of the perennial drought in USK river in recent years. The hydrological simulations provided a better understanding of streamflow changes in the USK basin. The study results can be helpful to maintain ecosystem services and sustainable water use in this region and in the Haihe River basin.