Estimation of the Maximum Physically Possible Precipitation in Saxony Using a Mesoscale Atmospheric Model

Abstract

A series of sensitivity studies have been performed to estimate the impact of presumed global warming on synoptic scale weather events. Within the framework of an epignostic study, mesoscale simulations of the Elbe river flood (August, 2002) employing the COSMO-DE model of the DWD have been carried out. The first set of runs was realised on a model domain size of 201 x 201 grid points with different temperature offsets at constant relative humidity. The results gave no hints on enhanced area accumulated rain sums in a warmed climate. Different temperature offsets at constant relative humidity does not result in significantly changed rain sums with respect to the reference run (climate as is). Increasing the water vapour mixing ratio so far, that the relative humidity increases, the total rain amounts increase, too. The observed rain sums originate from both thermodynamic and hydrodynamic effects (superposition of stratiform, convective and orographic rain contributions). An enhancement of the absolute water vapour mixing ratio at higher temperatures is indeed a necessary, but not a sufficient condition to enhance the rain formation. For example, a displacement of rain-promoting synoptic features might counteract rain formation, when the superposition of processes from different scale is not ensured any longer in a changed atmospheric system.