Urban cooling island effect of main river on a landscape scale in Chongqing, China

The condition of urban surfaces determines, to some extent, the atmospheric physical environment produced by the surfaces. Riverine water, which forms "urban cooling islands" (UCIs), is a typical natural urban element and an indispensable land cover type that plays an important role in improving the urban heat environment. The main river in Chongqing, China, was selected for a study of the spatial and temporal evolution characteristics of the UCI effect and analyze their coupled relationships with different types of urban land use and granularity levels. The UCI intensity and turning temperature were quantified based on the land surface temperature (LST) difference and the distance gradient of the surrounding landscape. The results indicate that (1) the main river is a lower-temperature zone for Chongqing City during daytime in the spring, and daytime and nighttime in the summer, and the highest-temperature zone during nighttime in the spring. (2) The correlation between the LST changes for different land uses, and the landscape index of class level shows that the smaller the value of the landscape area index (LAI) and landscape shape index (LSI), the smaller the variation of the LST. Conversely, the larger the LSI of the patch, the greater the degree of determination of the LST value. (3) Different land uses cause different LST changes in the buffers. The mean change occurs at 400 m for the impervious surface, at 362.5 m and 262.5 m for lawn and bare land, respectively, and at 462.5 m for forest and farmland. (4) Impervious surfaces are the most susceptible to the UCI effect of the nearby water bodies, while farmland is the least susceptible. The heat absorption and heat dissipation capacities of farmland are greater than those of impervious surfaces in the buffer zone. These results may help to plan and optimize the layout of urban land use around riverine water.