The relation between land-cover and the urban heat island in Northeastern Puerto Rico

Population growth and industrialization are causing rapid urbanization throughout the tropics, resulting in elevated temperatures within urban areas, a phenomenon known as the Urban Heat Island (UHI). One such example is the city of San Juan, Puerto Rico, where intense urbanization has caused the formation of a pronounced UHI. Our objective in this study is to quantify the UHI created by the San Juan Metropolitan Area over space and time.

We collected temperature data using mobile transects and fixed-station transects spanning along several urban-rural gradients to show the UHI created by San Juan. We also used this data to examine the relation between average temperature and upwind vegetation. Regression analysis of upwind vegetation vs. average temperature was used to predict temperature based on land-cover change over time.

The data show the existence of a nocturnal UHI, with nighttime urban-rural temperature differences (ΔT_U-R) of up to 3.02°C. Comparisons of diel temperature trends at urban, grassland, and forested sites indicate that canopy cover is needed to reduce daytime UHI effects. The results also shows that the UHI is encroaching on the Luquillo Mountains which may alter the water supply for San Juan. Temperature was predicted best (r² = 0.94) by vegetation in southeasterly upwind directions within 180 meters of the sensor, and under a ‘business as usual' urbanization scenario, over 140 km² of land that showed no signs of UHI in 2000 will have a UHI between +0.4°C - +1.55°C on average by 2050. Furthermore, over 130 km² of land area with a UHI between +0.4°C and +1.4°C in 2000 will have a UHI of +1.55°C on average by 2050.