Water scarcity is a main constrain for sustainable development in semi-arid regions. Social adaptive capacity theory offers a new idea for resolving water resource scarcity problem. The concept of Social adaptive capacity is put forward based on understanding the complex relation between human and ecosystem. As we known, nature is not a balanced system filled with nice biogeochemical cycles, circulating in a predictable pattern, but instead consist of complex and adaptive systems, where extreme events, such as floods and droughts, form a natural part of the reality. Nature is full of surprises, sudden shocks, which hit at random, resulting in complete reorganization of the playing field on which all biological life forms depend. In order to cope with randomness, shocks and extreme events, ecosystem has an inbuilt capacity to absorb shocks while maintaining function. This capacity of ecosystem is defined as the "adaptive capacity". Human systems can also plan and implement adaptation strategies in an effort to reduce potential vulnerability or exploit emerging opportunities even further. We call 'social adaptive capacity’ for this capacity of plan and implement adaptation strategies in an effort to reduce potential vulnerability or exploit emerging opportunities even further. Social adaptive capacity theory is a new for dealing with natural resource problem, and offers a new idea for resolving resource scarcity problem. There is a big challenge for human that natural resources are lack, especially water resources. Societies may be able to live with water scarcity, provided they can adapt through doing things with water in a better, more efficient way, and perhaps doing entirely other things than agriculture, then an index portraying the adaptive capacity of a society will provide a relevant picture of the impending challenges of that society.
In this paper, we introduce the origin of concept of social adaptive capacity for water scarcity, from the understanding that humans are completely intertwined with ecosystem, and discuss the structural components of social adaptive capacity for water scarcity by analyzing human ecosystem. Based on the relationships among factors of social adaptive capacity for water scarcity system and the analytic network process (ANP), we construct model of measuring social adaptive capacity for water scarcity. And the index system of measuring social adaptive capacity for water scarcity is constructed by on analyzing the characters of society, economy and culture in middle of the Heihe River Basin. Taking Ganzhou district in middle of the Heihe River Basin for study area, this paper does case study on measuring social adaptive capacity for water scarcity. The results are drawn follows: (1) The level of social adaptive capacity for water scarcity is not high in Ganzhou, whose index is 2.411, it means that social resource should be mobilized in process of solving water scarcity problems. (2) Among eight irrigation regions in Ganzhou, there is a different numerical value of social adaptive capacity for water scarcity, Yingke's is the highest, whose index is 2.625; Shangsan's is the lowest, whose index is 2.210. (3) In system of social adaptive capacity for water scarcity, the function of social order is the largest, social regime is second, cultural resources is last, in Ganzhou. So we should attach importance to cultivate cultural resources of Ganzhou. (4) In Ganzhou, two key resources are scarcity in system of social adaptive capacity for water resources. The levels of natural population growth rate and water consumption per capita are lower, social justice and awareness of water conservation of two indexes are higher. However, people's sense of security and trust are scarcity, clear power, managerial capacity and social and economic resources also should be improved. This paper discusses social adaptive capacity is a real resources to achieve water resources sustainability, aiming at offering a new method for research of water resources sustainability, providing scientific support for decision-making to adapt new social, economic and institutional tool to achieve water resources sustainability.