The Dynamic Relationship between Air and Land Surface Temperature within the Madison, Wisconsin Urban Heat Island

The urban heat island (UHI) effect, the phenomenon by which cities are warmer than rural surroundings, is increasingly important in a rapidly urbanizing and warming world, but fine-scale differences in temperature within cities are difficult to observe accurately. Networks of air temperature (T-air) sensors rarely offer the spatial density needed to capture neighborhood-level disparities in warming, while satellite measures of land surface temperature (LST) do not reflect the air temperatures that people physically experience. This analysis combines both T-air measurements recorded by a spatially-dense stationary sensor network in Dane County, Wisconsin, and remotely-sensed measurements of LST over the same area-to improve the use and interpretation of LST in UHI studies. The data analyzed span three summer months (June, July, and August) and eight years (2012-2019). Overall, T-air and LST displayed greater agreement in spatial distribution than in magnitude. The relationship between day of the year and correlation was fit to a parabolic curve (R-2 = 0.76, p = 0.0002) that peaked in late July. The seasonal evolution in the relationship between T-air and LST, along with particularly high variability in LST across agricultural land cover suggest that plant phenology contributes to a seasonally varying relationship between T-air and LST measurements of the UHI.

Automated summary

The urban heat island (UHI) effect, where cities are warmer than rural areas, is increasingly important in a rapidly urbanizing and warming world. This study found that air temperature (T-air) and land surface temperature (LST) show greater agreement in spatial distribution than in magnitude, with a complex relationship that varies with plant phenology.