Before revision:  Using the average R from January 21 to 23, 2020 as a proxy of non-intervened transmission intensity, we find, under a linear regression framework for 100 Chinese cities, high temperature and high relative humidity  reduce the transmission of COVID-19 with a significance level of 1\% and 5\% , respectively, even after controlling for population density and GDP per capita of cities.
After revision:  Using the average R 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 reduce the transmission of COVID-19 with a significance level of 1\% and 5\% , respectively, even after controlling for population density and GDP per capita of cities.