Temporal and spatial scaling effects of parameter sensitivity in relation to non-point source pollution simulation

Abstract

Scale represents an important concept in all scientific disciplines, but the scaling effect related to non-point source (NPS) pollution simulation and sensitivity parameters has not yet been reported. In this study, the sliding window, the Fourier amplitude sensitivity test and the nested watershed idea were used with the Soil and Water Assessment Tool (SWAT) model to explore the temporal and spatial scaling effects of parameter sensitivity in a typical watershed of the Three Gorges Reservoir Region, China. The results indicated that a great scaling effect could be observed at varying spatio-temporal scales, while the scaling effect would be transferred and amplified from the hydrological modelling to the NPS simulation. Soil properties such as SOL_K and SOL_BD were identified as key parameters under smaller spatial and temporal scales, while channel-related parameters in terms of ALPHA_BF, CH_K and CH_N showed greater sensitivity at larger scales. Specifically, some parameters, such as CH_N, USLE_K, USLE_P and ERORGP, were always identified as key sensitive parameters for the sediment and NPS-TP simulations, but some parameters, such as CH_K, showed sensitivity only above a specific spatial scale (778 km2 in this study). These results could be used as a reference for studying the scaling effect of model parameter sensitivity and provide important information for model construction and the management of NPS pollution at different scales.