Assessment of urban cooling effect based on downscaled land surface temperature: A case study for Fukuoka, Japan

The phenomenon of urban areas becoming warmer than surrounding rural areas, known as urban heat island, is one of the biggest urban issues due to human activities. The study adopted random forests (RF) based downscaling land surface temperature (LST) to assess the surface urban heat island (SUHI) of Fukuoka, Japan. The LST images were first downscaled to 250 m spatial resolution, and then the seasonal and diurnal SUHI was identified. The results implied that the SUHI in summer daytime is the most significant while in winter nighttime is the least significant in the area. Through the bivariate Moran?s I test and zonal statistics, the cooling effect of the green-blue spaces were evaluated. The forest has the most substantial urban cooling effect with the average LST change occurs at a distance of about 1 km (maximum 6.32 K). The cooling effect of the sea is significant during daytime, whilst that of the lake/river and the cropland/grassland is not obvious. We concluded the urban population and land use and land cover (LULC) are significantly spatial correlated to UHI, and are important factors of considering the urban heat island (UHI) mitigation strategies.