Evaluation And Early Warning Research Of Water Resources Carrying Capacity In The Three Gorges Reservoir Area

Water resource has been considered as an irreplaceable and strategic resource to maintain the function of ecosystem on earth and support social and economic development.With the expansion of the socio-economic scale,harmonious coexistence between man and water is facing challenges,and water security has gradually become a bottleneck restricting the sustainable development of social economy.Under the background of"Ecological Priority,Green Development",the research on evaluation and early warning of regional water resources carrying capacity is of vital practical significance for achieving scientific management and control of water resources,promoting the high-quality development of regional social economy and the ecological civilization construction in river basins.In this paper,the Three Gorges Reservoir Area(TGRA)was selected as the study area,and system of the evaluation and early warning of regional water resources carrying capacity was put forward.Firstly,the evaluation index system of water resources carrying capacity was established.As an important index of the evaluation index system,the value of the water environmental capacity was calculated based on the NPS pollution model of the TGRA.Based on the aforementioned work,the characteristics of water resources carrying capacity at different spatial scales under different social and economic structure and ecological environment conditions were revealed,the driving factors of water resources carrying capacity were identified and early warning research of water resources carrying capacity in the TGRA in 2020 and 2030 were carried out.The main research contents and findings include:(1)Taking into account the requirements for research on evaluation and early warning of regional water resources carrying capacity,the research progress of water resources carrying capacity was reviewed.At present,the research on water resources carrying capacity is gradually changing from static research to dynamic research,from qualitative analysis to quantitative calculation,from situation evaluation to monitoring and early warning of water resources carrying capacity.The application of water resources carrying capacity research is more in line with the strategic water resources security management needs of the nation.It is urgent and necessary to conduct research on evaluation and early warning of water resources carrying capacity in TGRA scientifically and objectively.(2)The system of evaluation and early warning of regional water resources carrying capacity was put forward.Firstly,based on the interdependence and interaction between water resources system,social economy system and ecological environment system,the evaluation index system of water resources carrying capacity in the TGRA with three hierarchical structures,three subsystems and nineteen specific indicators was established.Secondly,as an important index,the value of water environmental capacity was calculated based on the NPS pollution model of the TGRA.Thirdly,the weight and classification criteria of the evaluation index system were determined,and the evaluation method of water resources carrying capacity of the TGRA was established.Fourthly,combined with the process evaluation of water resources carrying capacity based on the actuality year,the early warning method of water resources carrying capacity in the TGRA was put forward.(3)The value of water environmental capacity is an important index that cannot be directly obtained in the index system,and it was calculated based on the NPS pollution model of the TGRA.Under the design hydrological conditions(P=90%of the driest month),water environmental capacity of COD,TP,TN and NH₃-N in the TGRA were 189133.88,5534.10,845.61 and 9110.81 t/a respectively.The value of water environmental capacity of the TGRA was estimated to be 155.181 billion from three aspects:sewage treatment replacement cost,social and economic benefits and ecological benefits.(4)The characteristics and driving forces of water resources carrying capacity at different spatial scales under different social and economic structure and ecological environment conditions were revealed.The water resources carrying capacity in the TGRA displayed a significant regional imbalance,showing a spatial trend of increasing from west to east,from the tail of the region to the head of the region.At the district and county scale,the water resources carrying capacity of Dadukou District was the weakest,with the evaluation grade being class V and Wuxi County being the strongest,with the evaluation grade being class I.On the scale of reservoir area,the water resources carrying capacity was strongest in the head region of the reservoir area,with the evaluation grade being class II,and the evaluation grade was class III in the middle region and class IV in the tail region.On the scale of main function regionalization,the water resources carrying capacity of key ecological functional area was better,with the evaluation grade being class II and key development area being weaker with the evaluation grade being class IV.Among the three subsystems,water resources per capita,urbanization level and value of the water environmental capacity have a significant strong correlation with water resources carrying capacity,which were the main driving factors of water resources carrying capacity.(5)The process evaluation of water resources carrying capacity in 2020 and 2030 and the early warning status of water resources carrying capacity were carried out.In 2020,the total resident population of the TGRA would reach 216.491 million,the urban population 14.987million and the total water demand 5,373.7 million m3.In 2030,the total resident population of the TGRA would reach 24.118 million,the urban population 19.357 million and the total water demand 5,359.2 million m3.Based on the results of process evaluation of water resources carrying capacity,the early warning grades of water resources carrying capacity in 2020 and2030 were classified.In 2020,there would be 0,7,6,10 and 3 districts/counties in red,orange,yellow,blue and green warning state respectively.In 2030,there would be 0,4,8,10 and 4districts/counties in red,orange,yellow,blue and green warning state respectively.Early warning situation of water resources carrying capacity in the TGRA would improve.The main cause of early warning situation was that the rapid development of economy and society has led to the excessive utilization of water resources,which exceeds the supply ability.Change of natural environment,differences of natural endowment and water resources management mechanisms and policies were also unneglectable causes.