Connecting climate model projections of temperature change with observations at regional and local scales – REtuning Climate Model Outputs (RECMO method): the Carpathian Region

It is well known that the results of climate model simulations differ from observations, and accordingly such projections can lead to different future temperature characteristics for the same region of interest. While the relative changes described by different climate models are of similar magnitude, the absolute temperature characteristics (based on their relative performance compared to observations) can be so different. At different warming levels (WLs, where a given temperature threshold can be calculated from temperature projections relative to a reference period or observations) global climate models (GCMs) can provide valuable information on climate change at the global scale. The main uncertainty factor for different WLs is time relative to a reference period (e.g. 1976-2005). Moving from global to regional scales, from coarser (~150 km) to finer (~12 km) resolution, regional climate models (RCMs) are expected to provide more detailed information than GCMs. For example, RCMs can better capture precipitation extremes at finer resolutions than the driving GCMs, especially over regions with complex topography, illustrating the benefits of high-resolution modelling. Thus, the timing of reaching a given WL can be assessed at regional and local scales based on high-resolution RCM simulations and high-resolution observations available for the region of interest. The REtuning Climate Model Outputs (RECMO) method helps to reduce differences between different RCM simulations by reducing uncertainties arising from the different climates described by different climate models under different WLs. It should be noted that the reference is based on observations and not on the model outputs from which the WLs are determined.  It can be argued that the RECMO method may be too selective depending on the performance of the climate models over the region (as RCMs with a relatively large cool bias may never reach that WL). Accordingly, the high-resolution raw and bias-corrected EURO-CORDEX and Med-CORDEX outputs are also used in the present work following the RECMO method for the Carpathian Region. Overall, the new concept helps to reduce differences between climate model simulations and leads to more reliable results with respect to possible future climatic temperature conditions for the region of interest. It should be emphasized that the concept is generally applicable to climate models over any region of the globe, the only limitation being the availability of data.