Kilometer-Scale Climate Modeling
Convection-resolving climate simulations for the greater Alpine region
In order to better understand the regional climate system and to improve regional climate change projections, a climate change simulation has been conducted using a convection-resolving model at horizontal resolution of 2.2 km across a greater Alpine domain, covering the region from Northern Italy to Northern Germany. To our knowledge, this is worldwide the first convection-resolving climate change simulation covering such a large domain (1100km x 1100km). Due to the computational cost, the simulations have been limited to 10-year long periods.
Validation against precipitation observations shows that the convection-resolving approach strongly improves the simulation of sub-daily precipitation in many aspects. This includes the diurnal cycle of mean and extreme summer precipitation, the diurnal cycle of wet-hour frequency, and the frequency-intensity distribution of hourly precipitation. This improved representation of short-term precipitation is a key for the assessment of flash flooding.
For the Alpine summer season, convection-resolving climate change simulations reveal that projected increases in both extreme daily and hourly summer precipitation follow theoretical expectations from the Clausius-Clapeyron relation (which expresses the increase of the water holding capacity of air with temperature), and amount to about 6-7% per degree warming. This result is of significant importance and the applicability of the 6-7%/K rate provides a surprisingly simple tool to climate change adaptation with respect to heavy precipitation events.
Continental-scale convection-resolving climate simulations
Our group is leading a major modeling project entitled "Convection-Resolving Climate Modeling on Future Supercomputing Platforms (crCLIM)" which is funded by the Swiss National Science Foundation through the Sinergia program. The crCLIM project aims to develop a European-scale convection-resolving climate modeling capability at a horizontal resolution of about 2 km using the next generation of supercomputing platforms. Our group performs, validates and analyzes convection-resolving climate simulations over Europe. Currently a first 10-year long simulation is about to be completed.
Publications
Leutwyler, D., Fuhrer, O., Lapillonne, X., Lüthi, D., and Schär, C.: Towards European-scale convection-resolving climate simulations with GPUs: a study with COSMO 4.19, Geosci. Model Dev., 9, 3393-3412, external pagedoi:10.5194/gmd-9-3393-2016call_made, 2016.
Ban, N., J. Schmidli, and C. Schär (2015), Heavy precipitation in a changing climate: Does short-term summer precipitation increase faster? Geophys. Res. Lett., external pagedoi:10.1002/2014GL062588call_made
Ban, N., J. Schmidli, and C. Schär (2014), Evaluation of the convection-resolving regional climate modeling approach in decade-long simulations, J. Geophys. Res. Atmos., 119, 7889–7907, external pagedoi:10.1002/2014JD021478call_made
Leutwyler, D., O. Fuhrer, X. Lapillonne, D. Lüthi, C. Schär (2015): Continental-Scale Climate Simulation at Kilometer-Resolution. ETH Zurich e-collection, DOI: external pagehttp://dx.doi.org/10.3929/ethz-a-010483656call_made (short description and animation), external pageonline video on Vimeocall_made.