Global Scaling of Rainfall With Dewpoint Temperature Reveals Considerable Ocean-Land Difference

Short-duration rainfall extremes are expected to intensify with warming at around 7%/K, following the Clausius-Clapeyron (CC) relation, causing concomitant increases in flash floods. Observed hourly rainfall extremes show consistent CC-scaling with dewpoint temperature across all land regions. Here, we use two global climate reanalysis products (ERA5 and MERRA-2) to examine consistency in scaling with observations, in ungauged regions and over the oceans. We find that reanalyzes underestimate observed scaling, but ERA5 provides better estimates than MERRA-2. Scaling rates at high latitudes and midlatitudes are similar to observations, at CC, while over the tropics mixed negative- and super-CC scaling rates are seen. We show underestimation of scaling rates over the tropics is related to deficiencies in simulations of extreme rainfall over orographically complex and convection dominated regions. Importantly, both reanalyzes indicate scaling rates over the ocean are substantially higher than over land, with implications for extreme weather events originating over the ocean.

Automated summary

Short-duration rainfall extremes are expected to intensify with warming at around 7%/K. Reanalysis products underestimate observed scaling, with ERA5 providing better estimates than MERRA-2. Scaling rates over the ocean are substantially higher than over land, with implications for extreme weather events.