Sensitivity of simulated precipitation to different RegCM configurations over the Carpathian region in the wettest year

Due to its high influence on agriculture, infrastructure, water management, and other areas, precipitation is one of the most important climate factors. Furthermore, climate change is likely to produce more extreme precipitation events and lead to an excess of surface water and floods, which have severe impacts on society. However, it is still one of the major challenges for climate models to realistically reproduce the regional patterns, temporal variability, and precipitation intensity due to the intricate interactions between atmospheric precipitation processes, including cumulus convection, large-scale circulations, planetary boundary layer processes and cloud microphysics. This is especially true for terrains with heterogeneous orography, like the Carpathian region.

For the sake of quantifying the uncertainty and improving the accuracy of the precipitation simulations of the RegCM4.7 regional climate model over the Carpathian region, we evaluate the performance of different physical options at 10 km horizontal resolution, using ERA-Interim reanalysis data as initial and boundary conditions. Altogether 24 simulations were carried out by using various combinations of the physics schemes (2 land surface, 2 microphysics, 3 cumulus and 2 boundary layer schemes) for the year 2010, which was the wettest year in the Carpathian region since the beginning of the regular measurements. Different parameterization combinations lead to different simulated climates, so their variance can serve as an estimate of model uncertainty due to the representation of unresolved phenomena.

The analysis of the RegCM ensemble indicates systematic precipitation biases, which are linked to different physical mechanisms in the summer and winter seasons. Furthermore, problematic interaction between some parameterizations causes large overestimation of the precipitation. Due to the different treatment of moisture in the schemes, there are differences not only between the representations of the precipitation cycle, but also in other climatological variables such as soil moisture, temperature and cloud cover. Based on the results, RegCM4.7 is the most sensitive to the applied convection scheme, but the interactions with the other schemes (e.g., microphysics and land surface) affect not only the total precipitation, but also the convective and stratiform precipitation in some cases.

Acknowledgements. Research leading to this study has been supported by the following sources: the Hungarian National Research, Development and Innovation Fund (under grant K-129162), and the National Multidisciplinary Laboratory for Climate Change (RRF-2.3.1-21-2022-00014).