Effect of Ambient Temperature on COVID 19 Infection Rate: Evidence from California

Abstract

Previous research has indicated that COVID-19 is less infectious in warmer temperatures under quarantine conditions. The evidence came from highly significant results from Chinese provincial data from February 1st to 12th of February; however, doubts persist about the results due to the authenticity concerns of Chinese data, the wide scope of Chinese provinces, and unidirectional epidemic during that time. In order to add further evidence, we analyzed California counties from March 22nd to the 5th of April. Taking a 7-day time lag (two more than the Chinese analysis to account for differences in healthcare); we find that ambient temperature again is a significant explanatory variable as to why cases spread faster in certain counties. On average each additional centigrade is associated with a 1.6 percentage point decrease in percent of new infections from a base of infectious individuals. Considering the mean percentage increase is around 17%, this means that an increase of 1 degree is associated with an 8.2% reduction in infectiousness. These results corroborate prior evidence and indicate that ambient temperature has an effect on areas that enforce social distancing and lock-down measures.