Heat/mortality sensitivities in Los Angeles during winter: a unique phenomenon in the United States

• Published in: Environmental health 2018-05, Vol.17 (1), p.45-12, Article 45
• Main Authors: Kalkstein, Adam J, Kalkstein, Laurence S, Vanos, Jennifer K, Eisenman, David P, Grady Dixon, P
• Format: Article
• Language: English
• Subjects: Air masses; Casualties; DLNM; Extreme Heat - adverse effects; Extreme weather; Health aspects; Heat; Human mortality; Humans; Humidity; Los Angeles; Los Angeles - epidemiology; Mortality; Nonlinear Dynamics; Risk; Seasons; Wind; Winter heat waves
• ISSN: 1476-069X; 1476-069X
• DOI: 10.1186/s12940-018-0389-7

Extreme heat is often associated with elevated levels of human mortality, particularly across the mid-latitudes. Los Angeles, CA exhibits a unique, highly variable winter climate, with brief periods of intense heat caused by downsloping winds commonly known as Santa Ana winds. The goal is to determine if Los Angeles County is susceptible to heat-related mortality during the winter season. This is the first study to specifically evaluate heat-related mortality during the winter for a U.S. city. Utilizing the Spatial Synoptic Classification system in Los Angeles County from 1979 through 2010, we first relate daily human mortality to synoptic air mass type during the winter season (December, January, February) using Welch's t-tests. However, this methodology is only somewhat effective at controlling for important inter- and intra-annual trends in human mortality unrelated to heat such as influenza outbreaks. As a result, we use distributed lag nonlinear modeling (DLNM) to evaluate if the relative risk of human mortality increases during higher temperatures in Los Angeles, as the DLNM is more effective at controlling for variability at multiple temporal scales within the human mortality dataset. Significantly higher human mortality is uncovered in winter when dry tropical air is present in Los Angeles, particularly among those 65 years and older (p