Source: GeoHealth
In the United States, nearly 9% of adults suffer from asthma, and it is the most common lung condition affecting children. During extreme heat events, the risk for hospitalization caused by asthma symptoms such as wheezing, shortness of breath, and chest tightness is heightened.
Previous research connecting asthma risk or hospitalizations and extreme heat has focused on data from weather stations that capture measurements in only one static location, rather than a wide range of temperatures over different neighborhoods. Baltimore’s Code Red Extreme Heat Alert, for instance, reflects only daytime temperature and humidity measured from National Weather Service sensors at Baltimore/Washington International Thurgood Marshall Airport (BWI).
Baltimore has a high prevalence of asthma and asthma-related emergency department visits. The city is also economically and racially segregated, and minority and low-income residents are more susceptible to both the effects of asthma and the effects of living in urban heat islands, where temperatures can rise several degrees higher than surrounding areas.
To investigate the link between extreme heat and asthma attacks in Baltimore, Corpuz et al. linked location-specific temperature data with emergency room records. The researchers found 695 pediatric cases and 819 adult cases of patients hospitalized for severe asthma at Johns Hopkins hospitals during the months of June, July, and August from 2016 to 2022. They then geocoded each case to a specific address and neighborhood.
In previous work, the researchers built models that used known information about temperature and local topography to generate 1-meter-scale maps of daytime and nighttime minimum and maximum air temperatures between 2016 and 2022. To capture different means of heat exposure, the study also used 11 different indices for heat waves, based on factors such as how high temperatures rose, how long heat waves lasted, or how long temperatures stayed above a given minimum.
By using these higher-resolution data and broader heat wave definitions, the researchers detected between 44 and 423 neighborhood-scale heat events during the study period. In comparison, using National Weather Service station data alone led to detecting between 0 and 95 events and missing nighttime risk, therefore underestimating the full scope of heat exposure.
The team found that prolonged nighttime heat waves were connected to higher asthma hospitalization risk, suggesting that the urban heat effect may disproportionately affect residents’ respiratory health at night, especially in neighborhoods where residents are already socially vulnerable. The researchers suggest strengthening Baltimore’s heat alerts to reflect the dangers of nighttime heat as well as specific neighborhood-level risks. (GeoHealth, https://doi.org/10.1029/2025GH001501, 2026)
—Rebecca Owen (@beccapox.bsky.social), Science Writer
