Does city-water layout matter? Comparing the cooling effects of water bodies across 34 Chinese megacities.

As most cities are located around or near waterbodies, it is essential to assess the thermal effect of these waterbodies. This research focuses on 34 Chinese megacities as case studies to examine the spatial relationship between city-water layout and the thermal effect of waterbodies. Landsat-8 remote-sensing images acquired around noontime in summer were used to retrieve land surface temperatures (LST) and classify land cover. The results show that there are three types of city-water layout. For most cities, waterbodies have a cooling effect, and their mean cooling distance (ΔL) ranges from 431 m to 1350 m, with the maximum temperature difference (ΔT) ranging from - 2.21 °C to 7.83 °C. The cooling effect of waterbodies is also influenced by their spatial distribution, size, location, and background climate regions. The larger the percentage or area of waterbodies in a city, the shorter ΔL and the bigger ΔT. Waterbodies have the longest ΔL and the smallest ΔT when they are dispersed within the city, whereas they have the shortest ΔL and the largest ΔT when they are flowing through the city. The results suggest that the thermal effects of waterbodies should be seriously considered by urban planners to improve the urban microclimate.