Analysis of Daily Ambient Temperature and Firearm Violence in 100 US Cities

Abstract

ImportanceFirearm violence is a leading public health crisis in the US. Understanding whether and how ambient temperature is associated with firearm violence may identify new avenues for prevention and intervention.ObjectiveTo estimate the overall and regional association between hotter temperatures and higher risk of firearm violence in the US.Design, Setting, and ParticipantsThis cross-sectional study used distributed lag nonlinear models, controlling for seasonality and long-term time trends by city and pooled results overall and by climate region. The most populous cities in the US with the highest number of assault-related firearm incidence (ie, shootings) from 2015 to 2020 were analyzed. Data analysis was performed from October 2021 to June 2022.ExposuresMaximum daily temperature by city.Main Outcomes and MeasuresThe primary outcome was the number of assault-related firearm shootings by city.ResultsA total of 116 511 shootings in 100 cities were included in this analysis. The pooled analysis estimated that 6.85% (95% CI, 6.09%-7.46%) of all shootings were attributable to days hotter than city-specific median temperatures. This equates to 7973 total shootings (95% CI, 7092-8688 total shootings) across the 100 cities over the 6-year study period, although the number of total persons injured or killed would be higher. Estimated risk of firearm incidents increased almost monotonically with higher temperatures, with a local peak at the 84th percentile of the temperature range corresponding to a relative risk of 1.17 (95% CI, 1.12-1.21) compared with the median temperature. However, even moderately hot temperatures were associated with higher risk of shootings. Although significant, there was low heterogeneity between cities (I2 = 11.7%; Cochran Q test, P = .02), indicating regional or climate-specific variation in the daily temperature and incident shootings relationship.Conclusions and RelevanceThese findings underscore the importance of heat adaptation strategies broadly throughout the year to reduce shootings, rather than focusing on only the hottest days.