Simulating the hydrological impacts of intensive Soil and Water Conservation Measures in the Yellow River Basin Using a Distributed Physically-based Model

Intensive Soil and Water Conservation (SWC) has taken place in the Yellow River basin (YRB) to control soil erosion and river sediment, it has altered the eco-hydrological processes and particularly led to the runoff reduction. However, the SWC are rarely simulated explicitly in the hydrological models of the YRB. In order to understand its hydrological impacts, this study developed a SWC parameterization scheme in an existing distributed physically-based model (GBEHM). The hillslope SWC was parameterized as additional surface storage capacity and simulated together with hillslope hydrological processes. The check dams along the river networks were parameterized as reservoirs and simulated together with the flow routing. The improved model (GBEHM-SWC) had been calibrated and validated comprehensively using the observed river discharge and remote sensing-based evapotranspiration. The annual precipitation and runoff significantly decreased during 1982-2000 at the rate of -4.3 and -1.0 mm/yr, respectively. In the following period 2001-2019, the precipitation recovered at 3.2 mm/yr with a slight increasing in runoff at 0.2mm/yr. Compared to the previous period, the annual average precipitation and temperature increased by 27.3 mm and 0.85 ℃, whereas the observed runoff decreased by 4.3 mm. Therefore, we applied the GBEHM-SWC to quantify the impacts of climate change and SWC in the YRB, spatially and temporally. The SWC contributed to the annual runoff reduction by 3.8 and 3.7 mm (or 2.84 and 2.74 billion m³), respectively, in which the hillslope SWC measures accounted for 51% of the annual runoff reduction. Without the append SWC measures, the annual runoff would increase by 2.9 mm (or 2.17 billion m³) in the recent period due to the precipitation increase. Hillslope SWC and river-networks SWC have their largest impact on runoff reduction in the Longmen-Sanmenxia section and Toudaoguai-Longmen section, respectively. The parameterization scheme developed for the distributed model is useful for the watershed hydrological simulation and prediction under the intensive SWC implementation.