On the sensitivity of precipitation in convection-permitting climate simulations in the Eastern Alpine region

They are tested individually with regards to a reference experiment and evaluated against two high-resolution gridded (1 km grid spacing) observational datasets over Austria, for winter and summer seasons. Also, a simulation with WRF v3.7.1, using a similar experimental set up, provides an estimate for the model-dependency of precipitation biases. The added-value regarding coarser resolved (0.11 degrees grid spacing, i.e. similar to 12.5 km grid spacing) CCLM and WRF simulations from the EURO-CORDEX initiative, which were used as driving data, is discussed.

In agreement with previous studies, convection-permitting experiments show added-value compared to their driving data regarding precipitation extremes, the height-dependency and the mean diurnal cycle of precipitation in summer. However, CCLM at convection-permitting resolution suffers from a predominant wet bias in mountainous regions in winter, and a dry bias in the eastern Alpine forelands during summer. The latter is related to a significant underestimation of the spatial extent of the precipitation events that cannot be compensated by overestimated intensities as it happens mostly in the mountains.

This interplay is insensitive to the parameters tested. In contrast, WRF at convection-permitting resolution largely overestimates precipitation because of too large and too intense precipitation events, though there are improvements in summertime. Using a direct nesting strategy with an operational high-resolution (0.225 degrees grid spacing, i.e. similar to 20 km grid spacing) analysis product from numerical weather prediction as driving data improves seasonal biases in the 3 km CCLM domain, thanks to reduced (enhanced) frontal precipitation in winter (summer).