Watershed discretization based on multiple factors and its application in the Chinese Loess Plateau

摘要

The spatial discretization of watersheds is an indispensable procedure forrepresenting landscape variations in eco-hydrological research, representingthe contrast between reality and data-supported models. When discretizing awatershed, it is important to construct a scheme of a moderate number ofdiscretized factors while adequately considering the actual eco-hydrologicalprocesses, especially in regions with unique eco-hydrological features andintense human activities. Because of their special lithological andpedologic characteristics and widespread man-made vegetation, discretizationof watersheds in the Loess Plateau in Northern China is a challenge. Inorder to simulate the rainfall-runoff process, a watershed in the LoessPlateau, referred as Ansai, was spatially discretized into new units calledland type units. These land type units were delineated under a scheme offactors including land use, vegetation condition, soil type and slope.Instead of using units delineated by overlaying land use and soil maps, theland type units were used in the Soil and Water Assessment Tool (SWAT).Curve numbers were assigned and adjusted to simulate runoff, using the USNatural Resources Conservation Service (NRCS) curve number method. Theresults of the runoff simulation better matched actual observations.Compared to the results that used the original units, the coefficient ofdetermination (R2) and the Nash-Sutcliffe coefficient (E_NS) formonthly flow simulation increased from 0.655–0.713 and 0.271–0.550 to0.733–0.745 and 0.649–0.703, respectively. This method of delineating intoland type units is an easy operation and suitable approach foreco-hydrological studies in the Chinese Loess Plateau and other similarregions. It can be further applied in soil erosion simulation and theeco-hydrological assessment of re-vegetation.