3.2. Evaluation of regulation services
After a city enters the stable development stage, heat island effect, environmental pollution, too high urban population density, and poor social health, threatened safety and other social problems have gradually emerged. Due to the destroyed urban natural environment, the influences of the natural environment on human survival, life, and production are widely concerned. Therefore, the benefits of urban water bodies and green spaces have been extensively explored in order to arouse public awareness of nature protection. Subsequently, relevant evaluation index systems were established to evaluate the environmental loss and develop a reasonable and targeted restoration plan based on the key impact indices. Therefore, the targets of evaluation index systems were gradually changed from ecosystem supply services to regulation services (Table 3).
The regulation services of an urban ecosystem involve four aspects: hydrology, ecology, environment, and society. The evaluation indices of the regulation services of urban rivers and lakes involve the elements of six aspects: hydrological characteristics, water environment quality, structure and function of water ecosystems, waterfront spatial structure, landscape effect, and stress factors (Zhang et al. , 2005). The indices that fully reflect the pressure, state, and response of river basins, such as population density, annual GDP growth rate, water resources per capita, annual rainfall, forest coverage, and industrial wastewater treatment rate, should be selected to evaluate the health status of ecosystems (Yan et al. , 2008). In addition, the wind environment, light environment, building and surrounding environment can be selected to comprehensively evaluate the greening development potential and quantitatively analyze the cooling characteristics and cooling efficiency of vertical greening (Shi, 2018). In Wetland Ecosystem Health Evaluation Index System proposed by the Wetland Conservation and Management Center of the State Forestry Administration, the health status of wetland ecosystems should be evaluated in five aspects: water environment, soil, biology, landscape, and society (Qian et al. , 2016).
These evaluation systems comprehensively consider the ecological service functions of water bodies and green spaces in urban ecosystems for regulating climate and preventing floods, and can analyze the factors affecting the stability of urban ecosystems based on specific functional indices and evaluation results. The comprehensive evaluation based on water, soil, land, atmosphere reflects the interaction between various natural elements, so that the environmental problems can be explored and the health conditions of ecosystems can be judged by evaluation results for ecosystem restoration. Due to the enhanced awareness of ecological civilization and natural restoration in urban planning, the comprehensive evaluation of water bodies and green spaces is significant. In the comprehensive evaluation, some characteristic indices are integrated together to reflect the interaction between them and the characteristics of the urban blue-green space as a composite ecosystem and improve the evaluation system.