Quantitative analysis of lake-cooling effect in Hefei City, China, based on multispectral remote sensing and its response to urban expansion

Urban expansion has intensified the heat-island effect, and the negative impact on the natural environment has gradually become considerable. However, urban lakes can significantly alleviate the heat-island effect caused by urbanization. Based on four-phase multispectral remote-sensing images during 2005-2020, 17 lakes in the main and surrounding urban areas of Hefei, China, were selected as the objects of our research. Each lake's cooling intensity and distance were calculated; cooling-efficiency data for different lakes were compared and analyzed considering lake areas and regional differences. The following conclusions were drawn: (1) The mean temperature of the lake had a strong positive correlation with the cooling-intensity efficiency and the cooling-distance efficiency, and it was the leading influencing factor of the cooling-intensity efficiency and the cooling-distance efficiency. The mean explanation degree was as high as 63.33% and 51.70%, respectively. (2) The lake area and the distance from the lake to the city center had a negative correlation with the cooling-intensity efficiency and cooling-distance efficiency and were the secondary factors that affect the cooling-intensity efficiency and cooling-distance efficiency. (3) The lakes around the urban area were far away from the main urban area where the heat-island effect was most concentrated, the ability of absorbing the high surface temperature caused by the heat-island effect was limited, and the cooling-intensity efficiency and cooling-distance efficiency were reduced by ~ 6.6 °C/km² and ~ 607.47 m/km², respectively, compared with the lakes in the main urban area. (4) With urban expansion and the intensified urban heat-island effect, the cooling-intensity efficiency of lakes in the main urban area gradually increased, whereas the cooling-distance efficiency of lakes decreased.