Quantifying Urban Heat Island Effects in a Mountain Forest Tourism Area Using a Forest Reference Baseline

Xitou is a mid-elevation mountain forest region (1000–1200 m a.s.l.) in central Taiwan where intensive tourism infrastructure is embedded within an otherwise continuous forest ecosystem. This setting provides a rare opportunity to apply a spatially explicit monitoring framework to characterize urban heat island (UHI) effects using an ecologically meaningful forest reference state, rather than conventional urban–rural comparisons.

This study establishes a forest temperature gradient baseline based on year-long in-situ thermal observations from elevation-differentiated forest sites. The derived forest lapse rate exhibits pronounced diurnal asymmetry, with weaker daytime cooling and stronger nocturnal cooling, reflecting the combined influence of evapotranspiration, radiative processes, and boundary-layer stability. Expected forest temperatures at hotel elevations were then reconstructed from this baseline and compared with observed temperatures to isolate tourism-driven UHI intensity.

Results show that hotel developments generate a persistent warming of approximately 0.9–1.3 °C relative to the forest baseline. UHI intensity exhibits strong diurnal contrasts: one hotel shows pronounced nocturnal dominance, with nighttime warming nearly 1.8 times daytime values, indicating the importance of building heat storage and nighttime heating, while another shows comparable daytime and nighttime warming, suggesting substantial daytime anthropogenic heat emissions from tourism activities. Seasonally, UHI intensity is significantly stronger in winter and weaker in summer, contrary to typical urban patterns, highlighting seasonal modulation by forest evapotranspiration, which partially offsets anthropogenic heat during the growing season.

Despite the forest’s strong thermal buffering capacity, the results demonstrate that conversion of forest land to tourism facilities measurably intensifies local UHI, altering near-surface atmospheric stability and potentially affecting fog formation, boundary-layer processes, and forest microclimates. These thermal changes imply broader ecological impacts, including increased nighttime heat stress and disruption of forest–atmosphere energy exchanges.