2.1.1. Ecological benefits
Due to the accelerated urbanization process and dense urban buildings,
the local temperature, humidity, air convection and other factors of the
urban surface have been artificially changed, thus causing the change in
urban microclimate (Xu et al. , 2019). Many researchers
investigated the distribution pattern of the UHI effect (Peng et
al. , 2016), and the relationships between air temperature (Qiu et
al. , 2017), land surface temperature (Yu, 2018), and land cover (Gaoet al. , 2019), and their correlation with ecosystem service
values (Anjos and Lopes, 2017) and found that urban green space and
water bodies had a good UCI effect.
A blue space, as a low-temperature corridor, can effectively alleviate
the UHI effect. The shape and contour of water bodies are the main
factors affecting UCI (Dai and Yao, 2021). Due to the unique continuity,
linear waters can effectively divide the aggregation status of heat
islands, block the regional expansion of the UHI effect, and provide
heat dissipation channels for heat exchange between the internal and
external parts of urban heat islands (Cheng et al. , 2019).
Through the physical effect of water evaporation, a surface water body
can reduce the temperature of the heat island area well and the closer
it is to the center of the urban heat island, the stronger the cooling
effect is (Yue and Xu, 2013).
As a natural underlying surface for climate regulation, a green space
provides a city with ecosystem services maintaining biodiversity and
regulating the urban climate. Vegetation coverage, planting structure,
and width of green space affect the UCI effect (Anjos and Lopes, 2017;
Yang et al. , 2017), and can strengthen the temperature effect in
the horizontal direction of the water body. Compared with densely built
asphalt roads and concrete roads, a green space has a faster heat
absorption rate and a smaller specific heat capacity (Lo et al. ,
1997). Good physical shading can reduce the leaf surface temperature and
transpiration can prevent the air temperature from rising (Kobayashi H,
2005), thus alleviating the UHI effect.
Some scholars studied the relationship between green spaces and the
cooling effect of water and found that there was a nonlinear
relationship between green space vegetation coverage and the cooling
effect of water. In addition, the type of vegetation coverage also
affects the cooling effect of water (Table 1). Green spaces and water
bodies have a synergistic effect in reducing the ambient temperature and
their cooling effects on the surrounding environment are mutually
influenced (Robitu et al. , 2006; Wu et al. , 2018).
Therefore, in a limited urban area, the UCI effect can be maximized by
constructing a blue-green space in order to promote the development of a
city (Montazeri et al. , 2017). A blue-green space can provide the
habitat to maintain biodiversity and regulate urban climate, displaying
its ecological service function as a composite ecosystem.