New research highlights the necessity for additional exploration to deepen our comprehension of urban heat patterns in subtropical and tropical locales. This ensures that strategies to mitigate heat are based on the most reliable data possible. A recent study investigates how effective land surface temperatures (LSTs) are as substitutes for surface air temperatures (SATs) in subtropical regions that experience seasonal rainfall. Researchers utilized satellite remote sensing data to analyze how LST indicates human heat exposure in Miami-Dade County, Florida.
The recent findings demonstrate the critical need for ongoing research to better understand urban heat dynamics in subtropical and tropical areas, confirming that heat mitigation initiatives rely on the most accurate data available.
A recent article published in the journal PLOS Climate on October 2, 2024, investigates the effectiveness of using land surface temperatures (LSTs) as indicators for surface air temperatures (SATs) within subtropical, seasonally moist regions. Researchers at the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science explored how LST reflects human heat exposure in Miami-Dade County, Florida, utilizing satellite remote sensing data. The results of the study are significant for urban heat adaptation efforts, bringing up concerns about how accurately LST depicts outdoor heat exposure in this area and others.
Using Land Surface Temperature to Assess Heat Exposure
“Data from LST, obtained through satellite imaging, have traditionally been applied to estimate surface air temperatures—the temperatures experienced by individuals outdoors,” said Nkosi Muse, a Ph.D. candidate in the Abess Graduate Program in Environmental Science and Policy at the Rosenstiel School and the study’s primary author. “LST plays a crucial role in processes within the lower atmosphere and can be measured at high resolutions—this is vital for recognizing urban heat risks and guiding adaptive strategies, particularly as cities heat up due to climate change and urban expansion,” he explained.
The researchers noted that the effectiveness of LST as a proxy varies depending on geographical and climatic conditions. While this relationship is well-studied in temperate zones, less research has been conducted on LST and SAT correlations in subtropical regions with significant summer rainfall.
This study aimed to fill that gap by focusing on Miami-Dade County. Researchers utilized Landsat 8 remote sensing data from 2013 to 2022 to compare LST readings with air temperature data from local weather stations, examining the effectiveness of LST as a proxy for SAT across different conditions. Their results indicated seasonal fluctuations in the connection between LST and SAT, emphasizing the challenges of utilizing LST data in subtropical, moist regions.
Seasonal Trends of LST and Urban Heat Island Effect
The findings revealed that LST data effectively illustrated the distribution of heat throughout the county, particularly emphasizing the surface urban heat island (SUHI) effect—where urban regions exhibit higher temperatures than neighboring rural areas. This phenomenon was most significant in spring, with an average SUHI intensity of 4.09°C, notably greater than in summer when it averaged 3.43°C. Interestingly, LST peaked in May and June, contrasting the typical northern hemisphere trend, which sees the warmest three months in July and August.
In comparison, surface air temperatures in Miami-Dade County reached their peak in August, with the correlation between LST and SAT fluctuating greatly depending on the season. In winter, LST closely matched SAT, but the alignment diminished during the wetter fall months, and no significant relationship existed during the summer.
Challenges of Using LST as a Measure of Heat Exposure
Even though LST is a valuable tool for identifying heat distribution in urban settings, this study indicates its limitations as a reliable measure of the temperatures people endure in subtropical, seasonally wet regions like Miami-Dade. During rainy periods, LST may not accurately represent the heat exposure experienced by residents. The timing of LST data collection (11 AM ET/12 PM EST) might influence this, as it does not capture the hottest part of the day, particularly during humid, wet months.
“These findings stress the dangers of relying exclusively on LST for urban heat adaptation strategies in regions with climatic patterns that differ from temperate zones,” stated Amy Clement, an atmospheric sciences professor at the Rosenstiel School and a co-author of the study. “As global cities, especially in subtropical and tropical zones, face increasing risks from heatwaves and temperature rises, these results highlight the pressing need for more precise measures to effectively evaluate heat hazards and inform countermeasures,” she added.
Consequences for Urban Planning and Future Inquiry
The insights garnered from this study hold immediate significance for urban planners and policymakers engaged in developing heat adaptation strategies in subtropical and tropical regions. As Miami-Dade County advances new heat policies and the City of Miami unveils its inaugural “Heat Season Plan,” these findings should be integrated into future planning efforts. The study suggests that depending solely on LST could result in misinterpreting heat risks, particularly in the wet season when air temperatures can surpass surface temperatures by a considerable margin.
With urban areas facing mounting pressure to shield vulnerable populations from extreme heat, this research underscores the necessity for enhanced methods of measuring and addressing heat exposure in Miami-Dade. Relying on LST data to pinpoint neighborhoods vulnerable to heat may fail to capture the intensity of heat exposure in several areas, especially during the hottest months. This could potentially yield inadequate or misdirected adaptation strategies.
The study also paves the way for future investigations, particularly regarding how localized factors—such as vegetation, water bodies, or types of urban materials—impact surface energy balances and LST measurements. Gaining insights into these elements could heighten the precision of LST as an instrument for assessing heat exposure in varied urban landscapes.
