A system dynamics approach for water resources policy analysis in arid land:a model for Manas River Basin

The Manas River Basin in Xinjiang Uygur autonomous region,similar to other arid regions,is facing water constraints which challenge decision-makers as to how to rationally allocate the available water resources to meet the demands from industries and natural ecosystems.Policies which integrate the supply and demand are needed to address the water stress issues.An object-oriented system dynamics model was developed to capture the interrelationships between water availability and increasing water demands from the growth of industries,agricultural production and the population through modeling the decision-making process of the water exploration explicitly,in which water stress is used as a major indicator.The model is composed of four sectors:1) natural surface and groundwater resources;2) water demand;3) the water exploitation process,including the decision to build reservoirs,canals and pumps;4) water stress to which political and social systems respond through increasing the supply,limiting the growth or improving the water use efficiency.The model was calibrated using data from 1949 to 2009 for population growth,irrigated land area,industry output,perceived water stress,groundwater resources availability and the drying-out process of Manas River;and simulations were carried out from 2010 to 2050 on an annual time step.The comparison of results from calibration and observation showed that the model corresponds to observed behavior,and the simulated values fit the observed data and trends accurately.Sensitivity analysis showed that the model is robust to changes in model parameters related to population growth,land reclamation,pumping capacity and capital contribution to industry development capacity.Six scenarios were designed to investigate the effectiveness of policy options in the area of reservoir relocation,urban water recycling,water demand control and groundwater pumping control.The simulation runs demonstrated that the technical solutions for improving water availability and water use efficiency are not sustainable.Acknowledging the carrying capacity of water resources and eliminating a growth-orientated value system are crucial for the sustainability of the Manas River Basin.