Extreme precipitation response to climate perturbations in an atmospheric mesoscale model

Observations of extreme (sub-) hourly precipitation at mid-latitudes show a large dependency on the dew point temperature often close to 14% per degree-2 times the dependency of the specific humidity on dew point temperature which is given by the Clausius-Clapeyron (CC) relation. By simulating a selection of 11 cases over the Netherlands characterized by intense showers, we investigate this behavior in the non-hydrostatic weather prediction model Harmonie at a resolution of 2.5 km. These experiments are repeated using perturbations of the atmospheric profiles of temperature and humidity: (i) using an idealized approach with a 2 degrees warmer (colder) atmosphere assuming constant relative humidity, and (ii) using changes in temperature and humidity derived from a long climate change simulation at 2 degrees global warming. All perturbations have a difference in the local dew point temperature compared to the reference of approximately 2 degrees. Differences are considerable between the cases, with dependencies ranging from almost zero to an increase of 18% per degree rise of the dew point temperature. On average however, we find an increase of extreme precipitation intensity of 11% per degree for the idealized perturbation, and 9% per degree for the climate change perturbation. For the most extreme events these dependencies appear to approach a rate of 11-14% per degree, in closer agreement with the observed relation.