Thermal environment effects and interactions of reservoirs and forests as urban blue-green infrastructures

Blue-green infrastructures, including reservoirs, lakes, forests and green spaces, play important roles in the microclimate environment. This study investigated the effects of blue-green infrastructures on the surface temperature adjacent to 12 reservoirs in the Pearl River Delta area, China. The temperature of each reservoir and its surrounding environment was retrieved by Landsat Thematic Mapper (TM) remote sensing imagery. The relationship between the temperature fields around the reservoir and the influencing factors was analyzed with statistical analysis. The results showed that distance (D), underlying surface type, and reservoir capacity (V) had significant effects on the temperature fields around the reservoirs. The temperatures across distances of 0-100 m and 0-200 m away from the reservoir boundary had a linear relationship with distance. The effect of the reservoir on temperature gradually declined when the distance exceeded 200 m. In the 0-300 m range, a quadratic equation with an intercept best fitted the relationship between temperature and distance. Four types of underlying surfaces, including built-up land, bare land, sparse forest land and forest land, were quantified by the normalized difference vegetation index (NDVI). Subsequently, a quadratic model expressing the correlation between temperature and the NDVI was obtained. Moreover, the surface temperature at the reservoir edge was negatively correlated to V. Finally, a multiple nonlinear regression equation was found to effectively describe the influence of D, NDVI and V on temperature fields around reservoirs. The influence of reservoir and vegetation (i.e., NDVI) on the field and their contributions were calculated by mathematical methods. The effects of the reservoir and vegetation on the peripheral temperature interacted with each other; the influence of the reservoir and the vegetation on temperature declined and increased, respectively, as distance increased. By addressing the influence of reservoirs and forests on temperature fields and cooling contribution rates, this study provides more insight into the role of blue-green infrastructure in the urban thermal environment.