China’s COVID-19 Quarantine Marginally Exacerbated a Warm February 2020

Abstract:

In the midst of the coronavirus pandemic, east China experienced two consecutive months of exceptionally warm weather, with 28 cities observing their warmest January-February period on record. Coincident with these unseasonable temperatures, large areas of China faced restricted economic activity due to COVID-19 quarantines, which were subsequently associated with marked air pollution reductions. Because particulate pollutants can scatter, diffuse, and absorb incoming solar radiation, serving as net negative radiative forcing, a reduction in air pollution can yield warming at the surface. This study explores whether the warm February 2020 in east China was exacerbated by COVID-19 quarantines. Satellite imagery, surface observations, and numerical model analyses are used to characterize the effect of the quarantine on the exceptional warmth. February 2020 meteorological conditions are first simulated with baseline anthropogenic emissions using the Weather Research and Forecasting model coupled with chemistry (WRF-Chem) and repeated with reduced pollution proportionate to the COVID-19 quarantine (C19Q) period; this sequence is performed for four WRF-Chem configurations. The C19Q emissions reductions increased surface air temperatures, with warming concentrated in interior China due to the synoptic circulation pattern. A maximum temperature increase of 0.13°C was observed in Changde, roughly 300 km west of Wuhan. In contrast, warming was not observed over the haze-prone North China Plain, where mean northwest flow dispersed pollution offshore in both emissions scenarios. Though a seemingly minor increase in temperature, epidemiological research suggests marginal warming may have a non-trivial effect on SARS-CoV-2 transmission, especially when integrated over densely populated regions such as east China.