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

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 (R 2 ) and the Nash-Sutcliffe coefficient (E NS ) 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 ecohydrological 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.

Evaluation of land‐use change effects on runoff and soil erosion of a hilly basin — the Yanhe River in the Chinese Loess Plateau

“…The land-use data of 1975 were used, and the daily simulation results were summed to monthly values. As more than 95% of the sediment in the region is eroded in the rainy season from June to October (Xu, Fu, He, & Gao, 2012), the calibration for the sediment load was performed with the observational data from June to October, instead of for all months as was done for runoff. The calibration was performed using SWAT-CUP programme (Abbaspour, Vejdani, & Haghighat, 2007) following the procedure described in Appendix S1.…”

Variation in the sediment deposition behind check‐dams under different soil erosion conditions on the Loess Plateau, China

“…The underlying surface conditions and soil types in the two watersheds are very different. In the Yanhe watershed, the landform is a typical loess hilly-gully landscape, and the loess covering 86.4% of the watershed is derived from loess parent material, which is a windblown under-consolidated deposit that formed over the past 2.5 million years in arid and semi-arid climatic conditions and is very erodible due to its macropores, well-developed vertical jointing and susceptibility to collapse on wetting (Zhang and Liu, 2010;Xu et al, 2012). This region experiences intense soil erosion as a result of unreasonable land use management, low vegetation cover, erodible soils, and frequent high-intensity summer storms .…”

“…Severe soil erosion has led to the loss of approximately 10 million hectares of cropland per year worldwide, not only reducing the cultivable land for food production but also causing land degradation and river siltation (Onyando et al ., ; Pimentel, ). The Chinese Loess Plateau, located in the middle reaches of the Yellow River, is one of the most severe soil and water loss areas in the world; more than 60% of the land has been subjected to intense soil erosion with an intensity of 2000 to 20000 t/(km 2 ·a), causing riverbed uplift (3–8 m) and flood disasters in the lower Yellow River (Fu, ; Shi and Shao, ; Xin et al ., ). Soil erosion involves the processes of detachment, transport and deposition of soil materials by erosive rainfalls and runoff (Shi et al ., ).…”

A curve number approach to formulate hydrological response units within distributed hydrological modelling

“…Steep slopes cause reduction of initial abstractions, decrease in infiltration, and reduction of the recession time of overland flow, which in turn results in increased surface runoff. Today it is accepted that 25 the reference CN values are applicable for terrain slopes around 5 %, and several researchers have proposed empirical formulae for adjusting the CN-values to slope (Huang et al, 2006;Xu et al, 2011). much lower values, of about 30-40, should be employed to represent the significant infiltration losses in such basins (Efstratiadis et al, 2014a).…”