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

Abstract

BackgroundExtreme 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.MethodsUtilizing 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.ResultsSignificantly higher human mortality is uncovered in winter when dry tropical air is present in Los Angeles, particularly among those 65 years and older (p < 0.001). The DLNM reveals the relative risk of human mortality increases when above average temperatures are present. Results are especially pronounced for maximum and mean temperatures, along with total mortality and those 65 + .ConclusionsThe discovery of heat-related mortality in winter is a unique finding in the United States, and we recommend stakeholders consider warning and intervention techniques to mitigate the role of winter heat on human health in the County.

The health burden of fall, winter and spring extreme heat events in Southern California and contribution of Santa Ana Winds

“…This is one of the first research study investigating the morbidity burden associated with extreme heat events in the 'cooler' seasons in southern California. The only previous study to our knowledge that has investigated winter heat and health demonstrated that high winter temperature is associated with increased relative risk for mortality in Los Angeles County (Kalkstein et al 2018). Our study adds to these findings by demonstrating an explicit connection to a specific weather patter (i.e.…”

“…These studies indicate that even moderate heat drives health impacts. Moreover, it has been recently suggested that the health burden of relative heat extends beyond the summer season; one study found higher mortality in the presence of hot and dry conditions in Los Angeles County during the winter months, associated with 4.4 total excess deaths per day (Kalkstein et al 2018). However, by focusing on all-cause mortality, this previous study did not capture heat-morbidity signals or consider specific diagnoses, which may underestimate the overall impact of heat.…”

Santa Ana Winds of Southern California Impact PM2.5With and Without Smoke From Wildfires

“…Examination of projected health risks due to future wildfire risk and changes in SAW is warranted. Confounding the smoke‐health impacts associated with SAW and wildfires, SAW also drive coastal heat waves that incur their own health risks (Kalkstein et al, ), which will change in a warmer future as SAW‐driven heat waves become less frequent (Guzman‐Morales & Gershunov, ) but hotter (Hughes et al, ). The ventilation effect of SAW without wildfires, meanwhile, should be beneficial to respiratory health—a hypothesized effect to be examined and quantified in future research.…”

The Mortality Response to Absolute and Relative Temperature Extremes

“…It would also omit all extreme temperature anomalies that fall outside of the core of summer, e.g., the March 2012 event across eastern North America that brought some of the most anomalous conditions seen in recent decades relative to the time of year, yet values that, when compared to an overall annual temperature curve, do not stand out as extreme (e.g., March 2012, [19]). It would also likely neglect events in relatively unique climates, such as the extreme warmth that sometimes affects southern California in the middle of winter due to downsloping easterly winds from the Sonoran Desert, which has been shown to increase human mortality [20,21,22].…”