On the implementation of external forcings in a regional climate model – a sensitivity study around the Samalas volcanic eruption in the Eastern Mediterranean/Middle East

Abstract. Natural and human-historical archives document regional climate variations and extremes of the past 2500 years across the Eastern Mediterranean/Middle East. Earth System Models (ESM) can contribute to the interpretation of the variations in the paleoclimate data and the dynamics of the underlying mechanisms. State-of-the-art ESMs have a good temporal resolution but are spatially too coarse to adequately address regional processes. Here, we provide for the first time a regional climate model (RCM) output adjusted to past climates forcings covering the Eastern Mediterranean/Middle East at a 0.44° horizontal and up to hourly temporal resolution. CMIP6 external climate forcings of volcanic, orbital, solar and greenhouse-gas changes are implemented in the RCM COSMO-CLM (CCLM, COSMO 5.0 clm16). The sensitivity of the model to each of the implemented forcing is tested separately and in combination in a case study around the large Samalas volcanic eruption (1255–1264 CE) with strong socio-economic impacts in the study area. We evaluate the impact of the different implemented forcings compared with the standard CCLM model version for the present time. The orbital forcing is found to have the largest effect with cooler winter/spring and warmer autumn during the test period. The volcanic forcing has a strong cooling effect for a couple of years after the large volcanic eruption. Other climate forcings only show a smaller impact in the sensitivity study, while the improvements in simulated precipitation are mainly due to the higher spatial resolution than to a specific forcing. The study is the basis for the new 2500-year-long transient, fully forced RCM simulation. It offers an assessment of the implementation of forcings in the RCM, along with an enhancement of the simulations' skill through the use of the RCM. We aim to enhance our understanding of the role of single and joint forcings on climate variability and extremes, their underlying processes at the regional scale, potential climate-society interactions and address limitations and uncertainties.