Surface Urban Heat Island
Across 419 Global Big Cities
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Abstract
Urban heat island is among the most evident aspects of
human impacts
on the earth system. Here we assess the diurnal and seasonal variation
of surface urban heat island intensity (SUHII) defined as the surface
temperature difference between urban area and suburban area measured
from the MODIS. Differences in SUHII are analyzed across 419 global
big cities, and we assess several potential biophysical and socio-economic
driving factors. Across the big cities, we show that the average annual
daytime SUHII (1.5 ± 1.2 °C) is higher than the annual nighttime
SUHII (1.1 ± 0.5 °C) (<i>P</i> < 0.001). But
no correlation is found between daytime and nighttime SUHII across
big cities (<i>P</i> = 0.84), suggesting different driving
mechanisms between day and night. The distribution of nighttime SUHII
correlates positively with the difference in albedo and nighttime
light between urban area and suburban area, while the distribution
of daytime SUHII correlates negatively across cities with the difference
of vegetation cover and activity between urban and suburban areas.
Our results emphasize the key role of vegetation feedbacks in attenuating
SUHII of big cities during the day, in particular during the growing
season, further highlighting that increasing urban vegetation cover
could be one effective way to mitigate the urban heat island effect