The Soil and Water Assessment Tool (SWAT) model is widely used to simulate watershed streamflow by integrating complex interactions between climate, geography, soil, vegetation, land use/land cover and other human activities. Although there have been many studies involving sensitivity analysis, uncertainty fitting, and performance evaluation of SWAT model all over the world, identifying dominant parameters and confirming actual hydrological processes still remain essential for studying the effect of climate and land use change on the hydrological regime in some water-limited regions. We used hydro-climate and spatial geographical data of a watershed with an area of 3919 km2
, located on the Loess Plateau of China, to explore the suitable criterion to select parameters for running the model, and to elucidate the dominant ones that govern the hydrological processes for achieving the sound streamflow simulation. Our sensitivity analysis results showed that parameters not passing the sensitive check (p
-value < 0.05) could play a significant role in hydrological simulation rather than only the parameters with p
-value lower than 0.05, indicating that the common protocol is not appropriate for selecting parameters by sensitivity screening only. Superior performance of the rarely used parameter SOL_BD was likely caused by a combination of lateral and vertical movement of water in the loess soils due to the run-on infiltration process that occurred for meso-scale watershed monthly streamflow modeling, contrasting with traditionally held infiltration excessive overland flow dominated runoff generation mechanisms that prevail on the Loess Plateau. Overall, the hydrological processes of meso-scale watershed in the region could be well simulated by the model though underestimates of monthly streamflow could occur. Simulated water balance results indicated that the evapotranspiration in the region was the main component leaving the watershed, accounting for 88.9% of annual precipitation. Surface runoff contributed to 63.2% of the streamflow, followed by lateral flow (36.6%) and groundwater (0.2%). Our research highlights the importance for selecting more appropriate parameters for distributed hydrological models, which could help modelers to better comprehend the meso-scale watershed runoff generation mechanism of the Loess Plateau and provide policy makers robust tool for developing sustainable watershed management planning in water-limited regions.
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