A US-based analysis of the ability of the Clausius-Clapeyron relationship to explain changes in extreme rainfall with changing temperature

Numerous papers have shown links between >99th percentile hourly precipitation and daily temperature (P-extreme versus T), often explained using the Clausius-Clapeyron (CC) relationship. The CC relationship predicts an approximately 7% increase in precipitation intensity per degree celsius. However, recent analyses indicate that the P-extreme versus T rate can be larger than the CC prediction. In this work, we analyze the P-extreme versus T rate with an automated method across the contiguous U.S. using station data aggregated on a 161km grid. To evaluate controls on P-extreme versus T, we isolate convective storms to evaluate whether greater than CC rates are due to the transition between storm types or are a feature of convective storms at high T. We repeat the analysis using dew point to assess whether T control on extreme P is indeed a matter of moisture availability. When evaluated using both T and dew point, the northeastern U.S. is most likely to exhibit a greater than predicted P-extreme versus T rate (57% of the region when using T). At 56% of these points, the>CC rates appeared to occur entirely because of a transition between frontal and convective storms. At 30% of these sites, a greater than CC relationship appeared to occur entirely because of greater than CC scaling in convective intensity. At 11% of sites neither was found to be significant, and at 3% both were found to contribute significantly. This analysis suggests that>CC scaling is not prevalent everywhere in the contiguous U.S., and in regions where it does occur, it can be due to multiple causes.