Regional climate models have frequently been shown to add value over GCMs. Questions are related to what added value is and how it can be assessed.
What is added value?
Added value of high-resolution regional climate models with respect to the underlying global climate models means that they are better at representing processes in the climate system and thereby better at simulating regional climate including its variability and trends. It could also mean that they are better at accurately projecting future climate change.
In principle, added value in RCMs over coarse-scale GCMs stems from the RCMs better resolving land-sea contrasts, height of mountains and various important processes in the climate system such as mid-latitude cyclones and frontal systems. While this constitutes added value on a basic level it can be more difficult to actually measure it. In particular, as large-scale conditions from a global climate model can be flawed, a regional climate model cannot necessarily change this situation even if some features may be better represented (Sørland et al. 2018).
How can added value be measured?
Added value for the historical period can be found from comparing output from the regional and global climate model to observations. Added value implying better accuracy for projecting future climate change is more difficult to assess. One possibility is to investigate how regional climate models perform in other regions where the climate is warmer, which to some extent could be seen as a proxy for a future warmer climate. Another, to evaluate to what extent historical trends are captured.
In particular, for the EURO-CORDEX regional climate models used in C3S, studies have shown added value for areas of complex terrain (e.g. Torma et al. 2015) and for daily-scale variability, including high-intensity precipitation (e.g. Prein et al. 2015). Potential added value from future climate model projections with so called convection-permitting models in their representation of heavy precipitation on sub-daily time scales is also to be expected (Kendon et al 2014), but, it is noted that such models are currently not part of the regional climate projections provided by C3S.
References
Kendon, EJ, NM Roberts, HJ Fowler, MJ Roberts, SC Chan, and CA Senior (2014) Heavier summer downpours with climate change revealed by weather forecast resolution model, Nature Climate Change, 4, 570–576, doi:10.1038/nclimate2258
Prein AF, Gobiet A, Suklitsch M, Truhetz H, Awan NK, Keuler K and Georgievski G (2013) Added value of convection permitting seasonal simulations. Clim. Dyn., 41, 2655–2677, doi:10.1007/s00382-013-1744-6.
Sørland S, Lüthi D, Schär C and Kjellström E, (2018) Bias patterns and climate change signals in GCM-RCM model chains. Environ. Res. Lett., 13, 074017, DOI: 10.1088/1748-9326/aacc77.
Torma Cs, Giorgi F, and Coppola E (2015) Added value of regional climate modeling over areas characterized by complex terrain—Precipitation over the Alps, J. Geophys. Res. Atmos., 120, 3957– 3972. doi: 10.1002/2014JD022781.
