Three Decades of Changes in the Urban Heat Island Effect in Denver, Colorado, Revealed by Landsat

Abstract

Rapid urbanization has imposed negative environmental impacts and contributed to global climate change on multiple scales. The urban heat island (UHI) is directly caused by urban expansion, dramatically increasing land surface temperature (LST). Despite the growing concern about the UHI in Denver, Colorado, few studies among the existing literature have addressed this issue. This study used United States Geological Survey (USGS) Landsat 5, 7, and 8 analysis-ready data (ARD) to characterize land cover changes and UHI in Denver for three decades (e.g., 1990, 2000, 2010, and 2020). Land surface temperature was derived from USGS Landsat Collection 2 ARD for twelve dates across summer, fall, and winter seasons in 1990, 2000, 2010, and 2020, and analyzed on both seasonal and annual scales. Land cover change (LCC) analysis detected a 13% increase in developed land cover and a 12% decrease in cropland and grass/shrubs from 1990 to 2020. The relationship between land cover and LST was modeled using ordinary least squares (OLS) and geographically weighted regression (GWR) analysis between land cover indices—e.g., the normalized difference vegetation index (NDVI), two-band enhanced vegetation index (EVI2), urban index (UI), and LST. The results from the regression models showed seasonal variability, spatiotemporal variations, and other underlying factors affecting the bivariate correlations. Finally, the seasonal and annual distribution and variation of UHI intensity were measured, and it was identified that the mean annual UHI intensity in 2020 was 1°C higher than that recorded in 1990, which illustrated a consistent spatial distribution throughout downtown Denver and the central areas of the city, while the intensity of UHI represented a more scattered distribution in the non-urban areas. The methods applied in this study can serve as a model for future research on other cities, and the findings can be used to inform sustainable urban planning and to mitigate the effects of UHI in Denver.