Study On The Theory And Method Of Water Resources Carrying Capacity In River Basins Under Climate Change

Under the dual influence of climate change and human activity,water resources and environmental issues associated with imbalanced water supply and demand in some basins have been aggravated.Hence,in the control of the traditional water availability,the evaluation on water resources carrying capacity(WRCC)does not meet the requirements of the strictest water resources management.Currently,the impacts of climate change on water resources demand and water environment quality in the future are rarely considered in the study on WRCC.Besides,the analysis of WRCC in the future is based on the different frequency of precipitation,which can not reflect the changes of WRCC in the future.Based on the statistical methods,the analysis of water quality does not reflect the relationship between water quality change process and water resource development and utilization.Therefore,it is urgent to consider the impact of water quantity,coupled with water quality on WRCC,and it has a great theoretical meaning to study the theory and method of WRCC in the river basin under climate change,and it also has a realistic value for realizing the sustainable development.In this study,the mechanism of climate change impact on the WRCC objects were analyzed.Based on it,the calculation model of the climate change impact on WRCC was put forward.Taking the Nanliujiang River Basin as an example,with the evaluation and screening of the climate model results,the built WRCC model was analyzed.The main work and the main achievements are as follows:(1)The theoretical framework of the impact of climate change on WRCCOn the basis of the concept diagram of the WRCC,the WRCC in the river basins under the climate change was defined.Then,from the point of water quantity and quality,the connotation of WRCC was analyzed,respectively.At water quantity level,firstly,the development and utilization of water resources should be no more than a renewable capacity of water resources;Secondly,the development and utilization of water resources should be subject to maintain ecological environment benign development,and ecological water demand should be paid attention to when the economic and social development are supported;At water quality level,firstly,the water environmental quality should meet the requirements of water quality goals of water function zones;Secondly,the water quality should meet the needs of water ecological system security and biodiversity.Then,the effects of climate change on water resources carrying subject mechanism were discussed,especially on the water quality,the impacts of water temperature and precipitation changes on the dilution and degradation of pollutants were emphatically analyzed.(2)The calculation model of WRCC under climate changeBased on the analysis of the mechanism of the climate change impact on WRCC,the climate model output module are selected as input factors of land surface system.The input-output relationship between the atmosphere system and land surface system are built.Then,based on the different water quality targest of water function regionalization,the water quantity and water quality mathematical model of each cell is set up.With the objective function of the largest available water resources in different water quality categories,and with the main control constraint equations,such as the water quantity and quality equation,the ecological and environmental water requirement equation,the optimization model of available water resources in different water quality categories is also set up.Finally,the dynamic trial equation of WRCC is built,and each sub model and each equation make up the calculation model of WRCC under climate change.(3)The study on the response of climate change on the water resources systems in the river basinThe impacts of climate change on the water resources systems were analyzed.The results show that compared with the baseline period(1963-2000),only the precipitation under RCP 4.5 in the next period(2013-2050)is increased.Spatially,the three scenarios are all present from the northeast to the southwest with an increasing trend.From the point of precipitation intensity,the light rain days occupy the most,with a value of approximately two-thirds of annual precipitation days.While the moderate rain takes the largest proportion of precipitation,which is about a half.Compared with the baseline period,the annual runoff under the RCP 4.5 is increased,with the values of 15.7 percentage,while the annual runoff under the RCP 2.6 and RCP 8.5 are reduced,with the value of-0,6 and-0.5 percentage,respectively.Spatially,the averaged runoff of many years shows the distribution characteristics of the high in the west and low in the east.In the same drainage conditions,the average CODcr concentration under the RCP 4.5 in 2030 is lower.The reason may be associated with the larger rainfall,which has a large effect on the dilution of contaminants in water.The average temperature under the RCP 2.6 is relatively low,and the precipitation is also relatively smaller,making the dilution effect of pollutants in water is relatively smaller.Hence,under the RCP 2.6 the average CODcr concentration of each river basin is high.In terms of water requirement,the agricultural water demand under the RCP 8.5 in 2030 is the largest,which is mainly caused by the less rainfall and the higher temperature,while the agricultural water demand under the RCP 4.5 is opposite.(4)The evaluation and prediction in different years of WRCCThe available water resources are used to calculate the value of WRCC by different quality,and a trial test is carried out based on the relationship between the domestic water demand and available water resources of class ??? under carrying level.The results show that in the present situation,the WRCC of GDP in the Nanliujiang River Basin is 132.68 billion yuan,which need 2.882 billion m3 water quantity to support the scale.While the WRCC of population is 6.621 million people,which need 352 million m3 water quantity to support its population.In 2030,the WRCC of GDP under the RCP 2.6,RCP 4.5 and RCP 8.5 are 312.13 billion yuan,514.44 billion yuan and 373.6 billion yuan,respectively,with the water quantity of 3.097 billion m3,4.567 billion m3 and 3.942 billion m3,respectively.While the WRCC of population are 7.042 million people,11.674 million people and 11.674 million people respectively,with the water qlantity of 462 million m3,763 million m3 and 552 million m3,respectively.Under the RCP 2.6,the WRCC of population in Bobai,Beiliu and Hepu are all decreased,while the WRCC of GDP are increased.The main reason is that the growth rate of per capita GDP in these regions is greater than the growth rate of the efficiency of production water use,which makes that the carrying population declines slightly.Of all the cities,only Yulin city and Bobai city are in a state of overload in the present situation,and the overloading degree are 1.14 and 1.08,respectively.In 2030,the overloading degree of Bobai city under the RCP 2.6 and RCP 8.5 are increased,which has reached to 1.29 and 1.19,respectively.Under the RCP 4.5,all administrative units are not in a state of overload,and the overloading degree declines compared with the baseline period.Under the RCP 8,5,only Bobai city is in a state of overload,and the overload degree increases,which reached to 1.19.