Satellite-derived subsurface urban heat island

Area of Science:

• Environmental Science
• Urban Climatology
• Remote Sensing

Background:

• The subsurface urban heat island (SubUHI) describes warmer underground temperatures in cities compared to rural areas.
• Measuring extensive underground temperatures in situ is challenging.
• Satellite data offers a potential solution for mapping the SubUHI.

Purpose of the Study:

• To reconstruct the subsurface thermal field of Beijing using satellite data.
• To analyze the spatial heterogeneity and temporal dynamics of the SubUHI.
• To investigate the occurrence of subsurface urban cool islands (UCI).

Main Methods:

• Utilized satellite-based Moderate-Resolution Imaging Spectroradiometer (MODIS) data.
• Employed a three-time-scale model to reconstruct the subsurface thermal field.
• Analyzed temperature data at various depths (shallower than 0.5 m, 0.5–10 m) and time scales (diurnal, annual).

Main Results:

• The SubUHI exhibits high spatial heterogeneity.
• At depths <0.5 m, SubUHI dominates, with diurnal extremes delayed by 3.25 h and 1.97 h per 0.1 m.
• A subsurface urban cool island (UCI) was observed at depths <0.05 m during spring daytime.
• At depths 0.5–10 m, annual extremes are lagged by 26.2 days per meter, with an average SubUHI intensity of 4.3 K.

Conclusions:

• Satellite-based remote sensing is effective for mapping urban subsurface thermal fields.
• The SubUHI's intensity and temporal dynamics vary significantly with depth.
• Understanding the SubUHI is crucial for urban planning and managing underground thermal environments.