Impacts of Bay Area Shelter-in-Place during COVID-19 on urban heat fluxes

The purpose of this project is to make quantitative connections between changes in social and economic activities in northern California urban areas and related Earth system environmental responses to the COVID-19 pandemic. Specifically, we will test the hypothesis that the absence of worker activities during Shelter-in-Place in the San Francisco Bay Area has detectably altered the infrared heat flux from parking lots, highways, and large industrial buildings, caused mainly by quantitative changes in the reflective properties (including brightness) in these different classes of urban surfaces. Satellite thermal infrared (TIR) sensor brightness temperatures from Landsat and Land Surface Temperature (LST) from ECOSTRESS will be mapped and quantified for all the large (> 0.25 km 2 ) urban features in the San Francisco Bay Area that have flat (impervious) surfaces, such parking lots, wide roads, manufacturing factory rooftops, refineries, etc. There is an urgent and unique timing requirement for this project, namely to visit numerous locations in the Bay Area during the Shelter-in-Place, such as large vacant lots and county parks, and make in situ measurements of ground thermal emission temperature from hand-held TIR sensors to validate and calibrate Landsat TIR and ECOSTRESS surface temperatures under the current (and presumably temporary) relatively clearer sky conditions. It is possible that the uniquely less polluted atmosphere is creating a detectable difference in surface heat flux that will be different next year at the same time(s). After all the large potential “dark object” urban features in the Bay Area have been delineated using sub-meter aerial imagery (source: NAIP 2018), the satellite LST time series we will develop, starting before Shelter-in-Place directives and continuing throughout the coming months, will be compared to LST maps acquired on (or near) the same dates from several previous years and into 2021. The overall regional differences in LST from these differentiated impervious surface features can serve as a key quantitative indicator of how COVID-19 has altered the aggregated Bay Area environmental footprint.