An Analysis of the Miami Urban Heat Island and its Potential Influence on Precipitation Distribution in South Florida

Urban areas tend to be consistently warmer than their rural surroundings as a result of lowered surface albedo, reduced evapotranspiration, and increased heat output and retention. The resulting temperature contrast between neighboring urban and rural areas is known as the Urban Heat Island (UHI). It is typically strongest at night, because urban substrates have higher heat capacities than dry soil. The Miami metropolitan area behaves as an urban heat island at times.

The elevated temperatures of UHIs, in conjunction with other properties common to urban areas, have been found to influence precipitation distribution in and around the urban center. The majority of studies examining UHI-precipitation effects have focused on inland urban areas with consistent synoptic patterns. It is not yet known how, or if, the Miami UHI influences precipitation distribution in South Florida, given the region's unique climate and topography.

This study furthers understanding of the Miami UHI and evaluates its influence on regional precipitation through analysis of surface station temperature data from the National Climatic Data Center (NCDC) and NOAA Cooperative Observer Network (COOP) in conjunction with South Florida Water Management District (SFWMD) 2 km x 2 km gridded precipitation data. The daily minimum temperature difference between designated urban and rural representative regions provides the working proxy for UHI intensity (defined as T_{min,urban -} T_min,rural). Preliminary temperature analysis indicates an average UHI intensity of +2.53° C with distinct seasonal variation and a daily minimum temperature maximum near the urban center. Daily UHI intensities are classified as strong (>2.78° C), average (2.28° C – 2.78° C), weak (0° C – 2.28 ° C) or negative (<0° C) (referred to as “urban cool islands”). Quantitative spatial precipitation analysis is then performed on daily and seasonal timescales and analyzed against derived UHI intensity.

A greater understanding of urban meteorological phenomena, including UHI-initiated precipitation, is imperative for a comprehensive assessment of how urban regions impact meteorological environments at the mesoscale level. The results of this study will ideally assist in improving urban planning and water resource management for the city of Miami and have potential applications for other coastal urban environments. Furthermore, the importance of such a study will only increase over time, given that humans continue to migrate to urban areas and anthropogenic climate change is predicted to increase the frequency and intensity of heat-related extremes.