Beware That COVID-19 Would Be Worse in Winter: A Study of a Global Panel of 1236 Regions

It is believe that weather conditions such as temperature and humidity have effects on COVID-19 transmission. However, these effects are not clear due to the limited observations and difficulties in separating impacts of social distancing. COVID-19 data and social-economic features of 1236 regions in the world (1112 regions at the provincial level and 124 countries with small land area) were collected. A Large-scale satellite data was combined with these data with a regression analysis model to explore effects of temperature and relative humidity on COVID-19 spreading, as well as the possible transmission risk by seasonal cycles. The result show that temperature and relative humidity are shown to be negatively correlated with COVID-19 transmission throughout the world. Further, the effect of temperature and humidity is almost linear based on our samples, with uncertainty surrounding any non-linear effects. Government intervention (e.g. lockdown policies) and lower population movement contributed to the decrease the new daily case ratio. The conclusions withstand several robustness checks, such as observation scales and maximum/minimum temperature. Weather conditions are not the decisive factor in COVID-19 transmission, in that government intervention as well as public awareness, could contribute to the mitigation of the spreading of the virus. As temperature drops in winter, the transmission possibly speeds up again. It deserves a dynamic government policy to mitigate COVID-19 transmission in winter.