Satellite Clear‐Sky Observations Overestimate Surface Urban Heat Islands in Humid Cities

Abstract

Satellite‐based thermal infrared (TIR) land surface temperature (LST) is hindered by cloud cover and is applicable solely under clear‐sky conditions for estimating surface urban heat island intensity (SUHII). Clear‐sky SUHII may not accurately represent all‐sky conditions, potentially introducing quantitative biases in assessing urban heat islands. However, the differences between clear‐sky and all‐sky SUHIIs and their spatiotemporal variations are still poorly understood. Our analysis of over 600 global cities demonstrates that clear‐sky SUHII is mostly higher than all‐sky SUHII, particularly in summer, daytime, and precipitation‐rich regions. Besides, clear‐sky SUHII typically exhibits stronger seasonal and diurnal contrasts than all‐sky SUHII, especially for cities located in humid regions. These discrepancies can be attributed mainly to the increased missing LST data caused by cloud enhancement in urban areas. Our findings highlight the tendency for clear‐sky observations to overestimate SUHII, providing valuable insights for standardizing the quantification of surface urban heat islands.

Feasibility of Urban–Rural Temperature Difference Method in Surface Urban Heat Island Analysis under Non-Uniform Rural Landcover: A Case Study in 34 Major Urban Agglomerations in China

“…To extend the comparison of multiple SUHII indices to a global scale, future studies should consider quantifying SUHI under rural regions with more diverse land cover types and varied climate backgrounds to facilitate its applicability. Additionally, it is important to note that our SUHII measurements were based solely on clear-sky observations, which may lead to an overestimation of regional averaged results [43]. Therefore, the improved high-resolution LST was recommended in future SUHII studies at a regional scale.…”

More Heavy Precipitation in World Urban Regions Captured Through a Two‐Way Subgrid Land‐Atmosphere Coupling Framework in the NCAR CESM2

“…Focusing on China, the simulated URE intensities are comparable with those in observations. The URE, in turn, weakens UHI intensities due to reduced surface incoming solar radiation in urban areas (Figure S3 in Supporting Information S1), thereby mitigating the positive biases in China as seen in the CTL run (Figures 2a and 2b, and Figure S2 in Supporting Information S1) (Vo et al, 2023;Yang et al, 2024).…”

“…Subsequently, grid-scale atmospheric forcings are sent back to the land model, uniformly driving land surface processes over all subgrid land units. Therefore, the conventional grid-scale land-atmosphere coupling framework cannot represent observed differences in atmospheric states between urban and surrounding rural areas (He, 2018;Vo et al, 2023;Yang et al, 2019Yang et al, , 2024. Furthermore, under this framework, urban impact signals at the grid-scale atmospheric states are largely filtered out by area-weighted averaging of subgrid land forcings, due to the small fractional coverage of urban areas (Zhao et al, 2021).…”