Study On Soil-Water Resources Carrying Capacity In Northwest Dry Farming Areas

Soil-water resources is the basic natural resources, which promoting social and economic development, supporting human and all the other organisms, and maintaining the good ecological environment. Soil-water resources carrying capacity system is a causal feedback system which contain social, economic and ecologic factor, and Soil-Water Resources Carrying Capacity (SWRCC) is a important index that measure the coordination degree of soil-water carrying capacity system and connect soil-water resources and social, economic, ecological system, the level of SWRCC often affect the living quality and social economic development. As the population growth and expansion of social economy, the obvious contradiction between supply and demand of soil-water resources induce a series of problems, for example soil erosion, soil-water environment pollution and so on. So with the guide of sustainable development to research and predict the SWRCC potential is important for optimizing allocation of soil-water resources, harmonizing the relationship between human, social economy, ecological environment and soil-water resources, keeping the regional sustainable development, promoting the reasonable utilization of soil-water resources and enriching the sustainable development theory.Most of current researches of carrying capacity focus on single factor of either water resources or land resources and have been limited by their one-sidedness and singleness. Follow the idea of sustainable development, under the premise of collecting material and system analysis the domestic and international achievements of SWRCC, this paper establishes a composite SWRCC indexes system according to the soil-water characteristics of northwest dry farming areas and influencing factors of SWRCC, then establishes quantitative calculating and comprehensive evaluation model about SWRCC. Take Shiyang River Basin and Guanzhong Region for case study, some research contents and conclusions are as follows:(1) The paper take water resources as carrying object, the social economy and ecological environment as carrying object. on the basis of meeting the basic ecological water requirement, In order to highlight the bigger proportion of water consumption that used for food, this paper establishes a quantitative calculating model about water resources carrying capacity which considering basic ecological water consumption, per-capita domestic water consumption, and per-capita water consumption of food and GDP. The water resources carrying capacity in Shiyang River Basin was quantitatively calculated in different living standards and different level of program planning by this model.The results show that water resources carrying capacity is reducing and the degree of overloading is rising with the improvement of people's living standards. Under the same living standard, the number of carried population is growing every year. And it can reach the level of overall well-off by 2010 in Shiyang River Basin. The results of second program reflect that the water resources carrying capacity has improved and the degree of overloading is reducing in planning level, but the basin was still overload in 2003, the RCI is 0.90 and 0.97 respectively in 2010 and 2020, the potential risk still existed.(2) This paper establishes a composite SWRCC indexes system, standards for different carrying degrees of SWRCC and method of determining the weight that combine the subjective and objective factor weights. The SWRCC indexes system which is composed of six sub-systems of water resources, land resources, technological efficacy, social, economic and ecological environment that contain 20 evaluation factors. The subjective factor weights based on fuzzy set decision theory are given to modify the entropy weights of evaluation factors in the model to allocate the weights more reliably, on the one hand fully consider the experts'subjective experience, on the other hand can solve the defect of objective weighting method depend only on simple data.(3) The paper use improved fuzzy comprehensive evaluation model based on entropy and fuzzy sets decision theory and improved Set Pair Analysis(SPA) comprehensive evaluation model to overcome the defect of losing information that affect the validity of traditional fuzzy comprehensive evaluation result and roughness of original SPA. In the improved fuzzy comprehensive evaluation model, the validity indexes is introduced to judge effectiveness of assessment results obtained from original fuzzy comprehensive evaluation and failed samples are reevaluated using the selection nearness principle which based on closeness degree to improve the credibility of comprehensive evaluation results. The improved SPA comprehensive evaluation model describe the samples'same, fuzzy and opposite feature more meticulously, and judge the SWRCC level with the same degree and set of potential, and through the positioning of the set of potential reflect the accuracy of assessment results and the convergence for their subordinate rank.(4) The improved fuzzy and improved SPA comprehensive evaluation models are applied to Guanzhong area, the result of research show that the SWRCC of Xianyang and Weinan in 2008 live in the condition of near overload which isⅡdegree, the level of SWRCC in other cities of Guanzhong area areⅢdegree that means load balance. The SWRCC order from excellent to poor is Baoji, Xi'an, Tongchuan, Weinan, Xianyang. The SWRCC of Baoji, Xianyang, Weinan are improved in planning years, but Tongchuan has the opposite result, SWRCC of Xi'an has increased in 2015, but decreased slightly in 2025.(5) The improved fuzzy and improved SPA comprehensive evaluation models are used to assess the SWRCC of Shiyang River Basin. The research show that SWRCC of Jinchuan isⅢdegree in 2015, whose level isⅣandⅤdegree respectively in 2015 and 2025; the SWRCC of Yongchang live in the condition of near overload that areⅡdegree in 2008 and 2015, it rose toⅢdegree in 2025; Liangzhou's SWRCC areⅡdegree in 2008, and increased toⅢdegree by 2025; compared to the other areas of Shiyang River Basin, the level of SWRCC in Minqin and Gulang in 2008 are lower, they live in theⅠdegree means overload, Gulang's SWRCC areⅡd egree in 2015 and 2025.