High-resolution Climate Simulation Using Double-nesting Method for Georgia

In this study, the latest version of the Abdus Salam International Center for Theoretical Physics (ICTP) Regional Climate Model is used to simulate the historical climate of Georgia for the 1986- 2005 period. Georgia is a small country with complex terrain, situated in the eastern part of the South Caucasus. It borders the Black Sea to the west, the Russian Federation to the north, Turkey and Armenia to the south, and Azerbaijan to the southeast. RegCM4.7.0 has been forced with the boundary conditions obtained from the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim reanalysis at 0.75° × 0.75° (EIN75). To simulate climate with high horizontal resolution and represent more special details for the complex terrain of Georgia the double-nested dynamic downscaling method has been used. The simulation with the 12-km resolution has been conducted by nesting the outputs of 50-km-resolution simulations for Georgia. The model capability was evaluated by comparing along with observations. Simulated annual and seasonal near-surface air temperature and precipitation was compared with the gridded observation data sets of the Climatic Research Unit (CRU) and University of Delaware (UDEL), as well as all available meteorological station datasets from Georgia. Results illustrate that the RegCM4 simulations by the double-nested method have the capability to depict quite well the spatial and temporal distributions of the surface air temperature and precipitation over Georgia. The double-nested method reproduces the observations better than the 50-km-resolution models. The topographical effects of complex terrains are detected better at 12 km resolution. The outcomes are especially important for the country from both social and scientific points of view as very few climate modeling studies exist for Georgia with high spatial resolution, and this is the first attempt to simulate the climate of Georgia with a 12 km resolution. This work was supported by Shota Rustaveli National Science Foundation of Georgia (SRNSFG) FR-19-8110.