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Simultaneous assessment of the summer urban heat island in Moscow megacity based on in situ observations, thermal satellite images and mesoscale modeling
This study compares three popular approaches to quantify the urban heat
island (UHI) effect in Moscow megacity in a summer season (June-August 2015). The
first approach uses the measurements of the near-surface air temperature obtained
from weather stations, the second is based on remote sensing from thermal imagery of
MODIS satellites, and the third is based on the numerical simulations with the mesoscale
atmospheric model COSMO-CLM coupled with the urban canopy scheme TERRA_URB.
The first approach allows studying the canopy-layer UHI (CLUHI, or anomaly of a nearsurface
air temperature), while the second allows studying the surface UHI (SUHI, or
anomaly of a land surface temperature), and both types of the UHI could be simulated
by the atmospheric model. These approaches were compared in the daytime, evening
and nighttime conditions. The results of the study highlight a substantial difference
between the SUHI and CLUHI in terms of the diurnal variation and spatial structure. The
strongest differences are found at the daytime, at which the SUHI reaches the maximal
intensity (up to 10°С) whereas the CLUHI reaches the minimum intensity (1.5°С). However,
there is a stronger consistency between CLUHU and SUHI at night, when their intensities
converge to 5–6°С. In addition, the nighttime CLUHI and SUHI have similar monocentric
spatial structure with a temperature maximum in the city center. The presented
findings should be taken into account when interpreting and comparing the results of
UHI studies, based on the different approaches. The mesoscale model reproduces the
CLUHI-SUHI relationships and provides good agreement with in situ observations on
the CLUHI spatiotemporal variations (with near-zero biases for daytime and nighttime
CLUHI intensity and correlation coefficients more than 0.8 for CLUHI spatial patterns).
However, the agreement of the simulated SUHI with the remote sensing data is lower
than agreement of the simulated CLUHI with in situ measurements. Specifically, the model
tends to overestimate the daytime SUHI intensity. These results indicate a need for further
in-depth investigation of the model behavior and SUHI–CLUHI relationships in general.