Divergent urbanization-induced impacts on global surface urban heat island trends since 1980s

Urbanization experiences different speeds and forms under diverse development stages across the globe. However, urbanization-induced impacts on long-term surface urban heat island intensity (I-s) trends across global cities and the regulators of such impacts remain understudied Here we estimate interannual trends in daytime I-s (i.e., urban-rural differences in surface temperatures) across 511 major cities for 1985-2020 using annual averages calculated using reconstructed land surface temperature data derived from >250,000 Landsat thermal images. Our study reveals that the global mean I-s growth rate is 0.156 degrees C/decade. We further examine I-s change associated with per 1% impervious land growth (denoted as beta) in each city throughout the research period and during different periods. The global mean beta is 0.018 +/- 0.025 degrees C/% (mean +/- 1 standard deviation) for the whole period, with greater values in humid than in arid climates; and the beta may change during different periods, e.g., it has more than tripled when urban impervious land exceeds 30%, indicating the spatiotemporally divergent impacts of urbanization on I-s trends across global cities. The spatial variations in beta across global cities are well correlated with rural vegetation abundance and precipitation but not with urban population. Among these three factors, rural vegetation abundance possesses the greatest standardized regression coefficient of partial least-squares model, signifying the critical role of biome background in regulating beta. The finding implies that future urbanization over densely vegetated regions should be more carefully and strategically planned due to the greater urbanization-induced surface warming effect.

Automated summary

Urbanization experiences different speeds and forms under diverse development stages across the globe. However, urbanization-induced impacts on long-term surface urban heat island intensity (I-s) trends across global cities and the regulators of such impacts remain understudied. Our study estimates the interannual trends in daytime I-s across 511 major cities for 1985-2020 and reveals that the global mean I-s growth rate is 0.156 degrees C/decade. We further examine the relationship between I-s change and impervious land growth, finding that the spatial variations in beta (the change in I-s associated with per 1% impervious land growth) are well correlated with rural vegetation abundance and precipitation but not with urban population.