| Weihe River is the largest branch of the Yellow River, flowing into the Yellow River at Tongguan of Shaanxi. The GuanZhong segment of Weihe River Basin is the core area in Shaanxi Province, where an important strategic position is taken up and significant role of the socio-economic development is played in West Shaanxi Province. However, with rapid socio-economic development of GuanZhong region and constantly increasing of human exploitation activities, there exists many problems in Weihe River Basin, such as, the severe situation in preventing or controlling floods, the obvious contradiction between supply and demand of water resources, the increasing intensification of water pollution, the slow progress in controlling soil erosion etc. All these issues have seriously blocked social and economic sustainable development of Weihe River Basin.Ecological risk assessment is a new rising field of research after the 1990s. It not only is an important branch of environmental risk assessment, but also is the scientific basis of environmental management and decision-making. Ecological risk assessment is a process that evaluates the likelihood that adverse ecological effects may occur or are occurring as a result of exposure to one or more stressors, and its research is involved in many subjects including environmental science, ecology, environmental and ecological toxicology, geography, disaster science etc. Regional ecological risk assessment is a significant branch of ecological risk assessment, and that is an integrated process of risk on studying many risk sources and risk receptors under the complex environmental background based on a large scale.This paper takes catchment area along Weihe River in Shanxi Province as an study area, by using 3S techniques, after processing and analyzing some remote sensing data from Landsat TM / ETM+ in 1990 and 2002, by introducing dynamic analysis model, calculating difference detection of LUCC, single and general dynamic degrees of LUCC, single and general changes about trend and state, change conditions of seven main land types were analyzed firstly in thirteen years.According to the definition and characteristics of ecological risk assessment, by using geographical information system, a variety of mathematical models and methods, under the theoretical framework and method's steps of American ecological risk assessment and regional ecological risk assessment, based on two land use classification maps of 1990 and 2002, we took seven types of landscape as risk receptors and human interferences as risk sources. Through constructing index's model of ecological risk and dividing risk sections, after setting classified symbols to two spatial distributing images of ecological risk index by using the geo-statistical methods, risk zoning maps of five classes, that is, low risk region, lower risk region, medium risk region, a little high risk region, high risk region were mainly acquired.Considering the status quo of frequent flood disaster in the lower reaches of Weihe River, the research divided the whole study area into nine sections including Xianyang city zone, Xi'an city zone, Gaoling county, Lintong district, Weinan city zone, Hua county, Huayin city, Dali and Tongguan county. Taking the administrative boundary of every zone as a unit, through comprehensive analyzing some impact degrees to natural hazards which are rainfall, terrain, water systems, passing flood and flood prevention projects, as well as impact degrees to vulnerability which indicate potential losing extents when encountering flood disaster. Applying to Analytic Hierarchy Process and factorial overlay methods, the graded image of integrated risk assessment for flood disaster was obtained by overlaying acquired images of natural and social attributes. The natural attribute image reflected the assessment of hazard's impact degrees and the social attribute image reflected the assessment of vulnerability's impact degrees.On the basis of the historical data in study area and landscape classified image of ETM+ in 2002, the paper mainly selected four risk sources of drought, flood, pollution and soil erosion. After describing and measuring the four major risk sources, analyzing exposure and hazard, confirming endpoint and dividing risk sections, through constructed model formula of general ecological risk values, we computed integrated risk probability, integrated ecological loss degree, integrated socio-economic vulnerability degree. At last, by overlaying the three parameters, comprehensive spatial distributing assessment image of five grades was acquired for regional major ecological risk sources.As the final aim of ecological risk assessment is to provide the digital-and-quantitative decision-making basis and theoretical support for the regional ecological risk and environmental management, in order to promote continuous improvement of regional ecological environment and maintain the stability of regional ecological structure and function, the research respectively proposed different risk management suggestions for risk region of five grades. At the same time, for reducing disaster risk and loss, we think it not only takes some measures to prevent and mitigate disaster of this region, but also strengthens prevention and management for the upper and middle reaches of the Weihe River. Only in this way, can socio-economic development of study area be in harmony with ecological environment from point to surface, from part to whole and from natural control to human control. Finally, some specific measures to prevent and mitigate disaster were put forward for four major risk sources in the study.The productions of this paper not only can provide a number of scientific basis for the environmental management and decision-making for risk managers aiming at different risk sections, risk sources and risk receptors, but also can provide some significant reference value for ecological environmental construction and sustainable development research in the lower reaches of the Weihe River. |
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