Abstract
Abstract. The spatial discretization of watersheds is an indispensable procedure for representing landscape variations in eco-hydrological research, representing the contrast between reality and data-supported models. When discretizing a watershed, it is important to construct a scheme of a moderate number of discretized factors while adequately considering the actual eco-hydrological processes, especially in regions with unique eco-hydrological features and intense human activities. Because of their special lithological and pedologic characteristics and widespread man-made vegetation, discretization of watersheds in the Loess Plateau in Northern China is a challenge. In order to simulate the rainfall-runoff process, a watershed in the Loess Plateau, referred as Ansai, was spatially discretized into new units called land type units. These land type units were delineated under a scheme of factors including land use, vegetation condition, soil type and slope. Instead of using units delineated by overlaying land use and soil maps, the land type units were used in the Soil and Water Assessment Tool (SWAT). Curve numbers were assigned and adjusted to simulate runoff, using the US Natural Resources Conservation Service (NRCS) curve number method. The results of the runoff simulation better matched actual observations. Compared to the results that used the original units, the coefficient of determination (R2) and the Nash-Sutcliffe coefficient (ENS) for monthly flow simulation increased from 0.655–0.713 and 0.271–0.550 to 0.733–0.745 and 0.649–0.703, respectively. This method of delineating into land type units is an easy operation and suitable approach for eco-hydrological studies in the Chinese Loess Plateau and other similar regions. It can be further applied in soil erosion simulation and the eco-hydrological assessment of re-vegetation.
Highlights
Watersheds are commonly spatially discretized in ecologic and hydrological studies
Land type units were delineated for the spatial discretization of a watershed in the Chinese Loess Plateau
The discretized factors were composed of land use and soil types, the hydrological condition of vegetation and slope
Summary
Watersheds are commonly spatially discretized in ecologic and hydrological studies. The purpose of spatial discretization is to objectively represent the differences in ecological or hydrological characteristics that exist within the watershed (Kumar et al, 2010; Hellebrand and van den Bos, 2008). A watershed is divided into units, which are treated as statistical objects or calculated units for statistical analysis or simulation. Spatial discretization can be regarded as a tradeoff between reality and a model represented by supported data. The more discretized factors and more detailed discretization, the more reliably the discretization represents the true watershed (Das et al, 2008); at the same time, more physical mechanisms and data are needed. Over-parameterization and scaling problems take effect (Doherty, 2003), so it is crucial to select a moderate number of discretized factors with major influences on the eco-hydrological processes, and have plenty of data and theory to support the discretization
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