Relative importance of water vapor and air temperature in the interannual variation of the seasonal precipitation: a comparison of the physical and statistical methods

The necessary condition for forming precipitation is the saturation of the atmosphere, and thus precipitation can be influenced by both water vapor and air temperature. Using the data from three reanalysis datasets for the recent 39 years, we examine the relative importance of water vapor and air temperature in the interannual variability of precipitation. Two methods are used to estimate the relative importance. One is the physical method, which is based on the very tight relationship between the seasonal precipitation and relative humidity as well as the definition expression of the relative humidity. The other is the statistical method, which uses linear regression and can be applied generally for many of the relationship issues. The goal of this study is to find out whether these two methods can obtain consistent results. For each method, an indicator is constructed to determine the relative importance of the water vapor and air temperature. The indicators of the two methods are calculated for each of the grid points. Comparisons include both their overall spatial distribution patterns and the spatial correlation of the two fields. It is found from the three datasets that over most of the grid points in the globe, the physical method and the statistical method can truly provide consistent results for the relative importance assessment. Both methods reveal that for every season, precipitation is majorly dominated by water vapor over the globe, with the dominance being mostly over the middle-low latitudes. However, there are still many areas where precipitation is dominated by air temperature, which appears especially over the middle-high latitudes.