Research On Water Accessibility And Ecological Water Requirement At Watershed Scale

Water is not only an extremely important and active factor in the natural and social environments, but also a basic natural and strategic resources that cannot be replaced to maintain the earth’s ecological system functions and support the development of social and economical system. With the continuous development of human society and the growth of demand for materials, it strengthen the exploitation of environmental resources, making natural resources shortage and even depletion, water shortages and pollution is one of the important issues we faced.In this paper, taking the Hanjiang River Basin as the study area, water accessibility evaluation model-SHRD is proposed based on DEM data, combing with the factors such as slope gradient, altitude, volume of runoff and water taking distance; the system of basin ecological water requirement is constructed from the overall basin, and then use SHRD model to evaluate the ecological water requirements satisfaction. The main conclusions are:(1) Water accessibility It is feasible to evaluate water accessibility by SHRD model, and exponential fitting is better than linear fitting, reflecting the water accessibility increases gradually from the Northwest Territories to southeast, and water accessibility is closely related to the distribution of river morphology.(2) The threshold value of catchment area81km is the reasonable threshold value in the process of extracting Hanjiang river system based on DEM data, and then test the extracted results using the length, drainage density and channel offset of the river. It turns out that the extracted river network is highly consistent with the actual river network, which could meet the need for furthe research and practical application.(3) Reference crop evapotranspiration Reference crop evapotranspiration in Hanjiang River basin ranges from413.47mm to609.7mm, and annual average value is511.19mm; spatial distribution of Reference crop evapotranspiration shows decrease from southeast to northwest, which is consistent with changes in precipitation, temperature and other climatic factors within watershed. It indicates the reference crop evapotranspiration is mainly influenced by temperature, precipitation and other climatic factors in this basin. (4) Ecological water requirement Total ecological water requirement is4.144×1010m3in Hanjiang River basin, where water demand of agriculture ecosystem is the largest, up to2.559×1010m3; that of wetland ecosystem is smallest, only0.475x1010m3, while the water demand of vegetation ecosystems and towns ecosystem are between them, respectively,0.535×1010m3and0.565×1010m3; on terms of three-level ecosystems, the largest water requirement is paddy,2.147×10m; while the water requirement of grass is minimum, only0.06×10m; other ecosystems are between them.(5) Ecological water requirement satisfaction Evaluation of ecological water requirement satisfaction in Hanjiang basin using SHRD model shows some increasing trend from southeast to northwest, and maximum value is985%and minimum value is31.6%。Ecological water requirement of satisfaction in each interval area difference between disparity, satisfaction between-25%to0took the largest area, about15.607×103km3, accounting for39.02%. Satisfaction of between25%and50%area of0, is the smallst region.