Linking Total Precipitable Water to Precipitation Extremes Globally

The relationship between extreme precipitation (EP) and precipitable water (W) is useful to assess design extremes and speculate on their expected changes with rising global temperatures. This study investigates the relationship between daily and longer-duration EP and corresponding W at a global scale by analyzing remote-sensed and reanalysis data sets from 2003 to 2019. An assessment of the consistency in the temporal trend across various W data sets reveals a consistent statistically significant upward trend during the period. This upward trend, while predominant worldwide, is especially significant over tropical land regions. W is found to generally be positively correlated with surface (dew point) temperature, suggesting a rise in temperature will cause a greater W over time. To assess whether EPs occur coincident with extreme W, the Concurrent Extremes Index (CEI) is proposed, which compares the cumulative distribution functions between the two variables and assumes a value of unity if ranks of the EP series are identical to that of the coincident W series, and zero with no correspondence. For EP (defined as the five largest 1-day events per year on average), a high CEI is pronounced across the tropics, except for rainforests. The W-EP relationship is noticeably weakened in nontropics, except the inland regions of North America and East Asia. An assessment indicates that as the duration of the EP becomes longer, the influence of W on EP decreases. However, the contrast in the W-EP relationship between the tropics and nontropics is found to become more pronounced as longer-duration EPs are considered.