Before revision:  Using the daily R values from January 21 to 23, 2020 as proxies of non-intervened transmission intensity, we find, under a linear regression framework for 100 Chinese cities , high temperature and high relative humidity significantly reduce the transmission of COVID-19, respectively , even after controlling for population density and GDP per capita of cities. One degree Celsius increase in temperature and one percent increase in relative humidity lower R by 0.0383 and 0.0224 , respectively.
After revision:  Using the daily R values from January 21 to 23, 2020 as proxies of non-intervened transmission intensity, we find, under a linear regression framework for 100 Chinese cities , high temperature and high relative humidity significantly reduce the transmission of COVID-19, respectively . One-degree Celsius increase in temperature and one percent increase in relative humidity lower R by 0.0383 and 0.0224 , respectively.