Super Clausius-Clapeyron scaling of hourly precipitation extremes: is it real or a statistical artefact?

The humidity of the air will rise due to climatic warming, approximately at a rate of 7 % per degree as given by the Clausius-Clapeyron (CC) relation. The same rate of increase is also the benchmark of changes in precipitation extremes with evidence from observational trends and future projection by climate models.

However, there are circumstances when changes in precipitation extremes do not obey the CC rate. For hourly rainfall observations, dependencies of precipitation extremes on (dew point) temperature of two times the CC rate (2CC scaling) have been derived from present-day climate variability. However, it is still unclear whether this high sensitivity is indicative for long term variability due to climate change. It has been argued in the literature that 2CC scaling is entirely caused by the statistical processing and has no physical meaning. However, a simple physical explanation of 2CC behaviour also exits. In this talk I will explain this controversy. Further, I will show results of high resolution convective permitting model simulations for present-day climate and a warmer climate, which support scaling rates of hourly extremes between 1 and 2 CC dependent on the region and season.　

Speaker: Geert Lenderink (KNMI)