Scenario analysis and forecasts of water environment carrying capacity in Nanjing City

The study of future development of regional water environment carrying capacity (WECC) is necessary to support the construction of regional ecological civilization. Taking Nanjing City as an example, a three dimensional indicator system of WECC based on the composite system of socioeconomic, water resources and water environment was established. A regionally applicable system dynamics model and six development scenarios were also designed. On this basis, the genetic algorithm was applied to projection pursuit optimization, and the genetic projection pursuit method was constructed to predict WECC under different scenarios in 2017-2030. The study showed that the WECC of Nanjing was increasing under each of the scenarios in 2017-2030, and the performance of promoting WECC was: comprehensive development scheme (30.1%) > water saving scheme (28.5%) > water pollution control scheme (24.2%) > economic optimization scheme (24.0%) > current pattern scheme (21.3%) > high population growth scheme (12.5%). Under the current pattern scheme, the WECC of Nanjing would be steadily improved, and exceed Level Ⅰ by 2027. This is to say, under the current development mode, the scale of Nanjing’s socio-economic development would be within the scale that could be supported by the water environment. The WECC under the comprehensive scheme was the fastest to reach Level Ⅰ. Under the high population growth scheme, the development level of WECC would be significantly hindered, and never reach Level Ⅰ during the study period. If Nanjing City adopted the model of population growth, economic optimization, water resource conservation and water pollution control, WECC would be improved faster.