Environmental Research Letters (Jan 2024)
Multi-city analysis of satellite surface temperature compared to crowdsourced air temperature
Abstract
Many urban heat studies have been conducted on a city-by-city basis, primarily focusing on summer days, overlooking the broader impact of background climate, seasonality, and diurnal cycle. Moreover, in some cities where there is a lack of observational data on urban air temperature ( T _a ), there has been a reliance on satellite-based land surface temperature (LST) to explore and predict the changes in near-surface thermal environments. However, it is still unclear how applicable LST is for exploring the temporal and spatial variation of air temperature across different seasons and background climates. To address these shortcomings, we used high-density crowdsourced T _a observations and satellite imagery to characterise the temporal variability of city-wide T _a and compare it with LST across 55 populated cities. Cities were selected according to the number of crowdsourced T _a measurements, percentage of clear sky pixels and global coverage. Results show that the temporal trends of city-wide LST and T _a agree more closely at night compared to daytime. During the day, the agreement is greater in winter, especially in colder climates. While the intra-urban spatial distribution of LST does not align with T _a , the city-average values are highly correlated. However, the strength of this correlation differs by season and time of day and is further influenced by background climate. If city-average trends are of focus, LST can be used as an indicator for exploring air temperature variations over time, particularly at night. LST can also be used for winter days in cities with temperate and cold climates. However, its application for summer daytime requires more caution, especially in arid cities. These findings provide new insights into the application of satellite-derived LST for exploring city-average temperature trends and variability.
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