Exploring the Influence of Summer Temperature on Human Mobility during the COVID-19 Pandemic in the San Francisco Bay Area

Abstract

Heat related illnesses are one of the leading causes of weather-related mortality in the United States, and heat extremes continue to increase in frequency and duration. Public health interventions include population mobility, including travel to central cooling centers or wellness checks on vulnerable populations. Using anonymized cellphone data from Safegraph’s neighborhood patterns dataset and gridded temperature data from gridMET, we explored the mobility-temperature relationship in the San Francisco Bay Area at fine spatial and temporal scale. We leveraged spatial variability in median income and temporal variability in COVID-19 related policies across two summers (2020-2021) to analyze their influence on the mobility-temperature relationship. We completed quantile regressions for a dataset stratified by income and year. We found that mobility increased at a higher rate with higher temperatures in 2020 than 2021. However, in 2021, the relationship reversed for several wealthier income groups, where mobility decreased with higher temperatures. We then augmented the analysis and calculated a panel regression with fixed effects to characterize the mobility-temperature relationship while controlling for temporal and spatial variability. This analysis suggested that all areas exhibited lower mobility with higher summer temperatures. However, similar to the results of the quantile regression, the rate of decrease in mobility in response to high temperature was significantly greater among the wealthiest census block groups compared with the least wealthy. Given the fundamental difference in the mobility response to temperature across income groups, our results are relevant for heat mitigation efforts in highly populated regions in current and future climate conditions.

Heatwave adaptation conditioned by everyday life: Analyzing interacting changes to daily activities during Pacific Northwest summers

“…In the activity level analyses, data sources range from subway turnstile data in New York City (Stechemesser and Wenz, 2023) to cell phone mobility data in Los Angeles County, Houston, and Tokyo (Ly et al, 2023;Gu et al, 2024;Tian et al, 2024;Kumakura et al, 2024). While all studies focus on overall activity levels during periods of extreme heat, Gu et al (2024) distinguish flows between neighbourhoods, finding reductions in short-distance travel during heatwaves and unchanging long-distance travel.…”

“…Four of the studies assess the impact of socio-economic inequalities on general heatwave activity levels, discussing that disadvantaged individuals may be especially vulnerable based on their activity changes, despite conflicting findings. Stechemesser and Wenz (2023), Ly et al (2023), andTian et al (2024) find that individuals in lower-income regions are less able to reduce mobility during heatwaves -the latter during both day and night -discussing potential factors such as increased work and personal obligations, the use of public transport to escape local heat conditions, and generally lower adaptive capacity. In contrast, Gu et al (2024) find that extreme temperatures disproportionately inhibit the activity of low-income individuals, contextualizing their results by citing a lack of travel options and less disposable income.…”

“…Climatically, the absolute temperature unveils how heatwave intensity, in a traditional sense, impacts adaptive responses during heatwaves. This factor is considered because prior mobility analyses have identified a range of activity changes during extreme temperatures (Stechemesser and Wenz, 2023;Ly et al, 2023;Gu et al, 2024;Tian et al, 2024) and specific usages of indoor cooling facilities (Derakhshan et al, 2023). In addition to absolute temperature, a heatwave's impact on heat stress is relative to a region's norm (Guirguis et al, 2018) -hence the often context-specific definitions of heatwave temperatures (Perkins and Alexander, 2013).…”

“…These inequalities manifest in the mobility behaviours of individuals during heatwaves -a complex, understudied process which shapes exposure to extreme heat. As extreme heat is estimated to cause 489,000 excess deaths globally every year (Zhao et al, 2021) and as heatwaves increase in intensity, frequency, and duration with human-induced climate change (Perkins-Kirkpatrick and Lewis, 2020), literature on extreme heat mobilities has been rapidly growing (Derakhshan et al, 2023;Stechemesser and Wenz, 2023;Ly et al, 2023;Gu et al, 2024;Tian et al, 2024). This literature has identified numerous adaptive mechanisms and intersections between heat exposure and existing inequalities.…”

“…The study period covers three summers after the start of the COVID-19 pandemic (2020COVID-19 pandemic ( , 2021COVID-19 pandemic ( , 2022, including periods both during and after the restrictive mobility policies implemented by governments to limit the spread of disease. Ly et al (2023), who focus on extreme heat in the San Francisco Bay Area from 2020 to 2021, find that even during stringent stay-at-home measures, extreme heat led to a range of mobility behaviour changes. This paper accounts for the influence of varying COVID-19 restrictions, which differ across jurisdictions and years (Ding et al, 2020;Bollyky et al, 2023), through a matched-pair algorithm that aims to isolate heat-related activity differences in each county.…”