The Nile Basin has been the focus of research on the links between climate variability, extreme events and social events over the last 2000 years of history. Unfortunately, we currently only have global climate and Earth system model data with low spatial resolution for this period. To understand how climate affects society, we must rely on proxy data, as global climate models lack the necessary regional process detail. Our goal is to enhance our understanding of the historical climate of the Nile Basin on a regional scale using the customized COSMO-CLM paleoclimate model. We intend to run simulations with COSMO-CLM (forced by MPI-ESM-LR) by using the “past2k” simulation set up with an optimized configuration for both the present (1979–2019 CE) and paleo periods (500–2000 BCE) at resolutions of around 50 and 12 km. In this approach, we tried to systematically consider orbital, solar, and volcanic influences, as well as changes in vegetation, land use, and greenhouse gas concentrations in the simulation. We found that the temperature simulations are overall in agreement with the reanalysis data and the observational record. However, it is worth noting that our precipitation simulations performed relatively weakly, especially in the Nile Basin.

Abstract. The past 2500 years were marked by major historical developments across the eastern Mediterranean, the Middle East, the Arabian Peninsula, and the Nile Basin from Lake Victoria to the Nile Delta. Modeling efforts by both the global and regional climate modeling communities remain limited in this region. Here, we address this gap by presenting the first transient regional climate simulation for the area spanning 2350 years, from 500 BCE to 1850 CE, using the COSMO-CLM model. The simulation reveals an exceptionally pronounced climatic response to the consecutive volcanic eruptions of 536 and 540 CE, which motivated an additional century-long ensemble experiment to investigate this interval in greater detail. The eruptions produce marked surface cooling through reduced incoming solar radiation and are accompanied by large-scale circulation anomalies. In the simulation, widespread cooling persists until around 550 CE, with boreal summers showing the strongest anomalies during the first two to three years after the eruptions. Precipitation responses display strong regional contrasts: anomalously wet conditions occur over the Mediterranean, the Middle East, and Southeast Africa, particularly during the climatologically dry Northern Hemisphere summer season, whereas the Sahara, the Arabian Peninsula, Central Africa, and Northeast Africa experience concurrent dryness concentrated in their respective rainy seasons. The most severe climatic anomalies occur within the first one to two years after the eruptions and gradually weaken over the following years.

Data related directly to the First Plague Pandemic [FPP] (541–750 CE) in the Byzantine Empire has been gathering for over a century. Initially, only textual evidence was used, resulting in varied interpretations. In recent decades, however, a wider range of materials from natural sciences and archaeology has been included in FPP reconstructions. The methods used to analyze and interpret these data differ across disciplines and have varying levels of margin of error. The cross-disciplinary use of such data, still in early development, has produced interpretations that are sometimes debated, mainly due to a lack of familiarity and ongoing communication among relevant fields. Even within the same dataset, like written sources, the persistent use of significantly different approaches has resulted in various FPP reconstructions. Our goal is to change that by reexamining both the original data from the eastern and central Mediterranean from the mid-sixth to the mid-eighth century and the methods behind them. We explore new data and apply methods from a broad range of disciplines to identify gaps and uncertainties and suggest ways to address them.

The Earth's climate is currently undergoing significant transformations, marked by increasing temperatures, more frequent extreme events, and shifts in precipitation patterns. To comprehend these changes on decadal to centennial time scales and contextualize current climate change, it is essential to leverage paleoclimatic data spanning centuries to millennia. This analytical approach enhances our insight into natural climate variability, trends, and extremes, facilitating projections, planning, and preparation for the future. Paleoclimate reconstructions, utilizing physical, chemical, biological, or detailed documentary records, offer valuable insights into climate conditions and variability across different historical periods. In contrast, climate models provide comprehensive information and data describing the entire climate system. Paleoclimate models specifically simulate the climate of past centuries to millennia by reconstructing the forcings influencing Earth's energy and, consequently, its climate. However, global circulation models with low horizontal resolution fall short in fully elucidating atmospheric pattern interactions and linking potential climate impacts contributing to significant societal events in history. Recognizing these limitations, regional climate models emerge as promising tools for a more realistic representation of topography and regional climate information pertinent to paleoclimate studies. In our investigation, we employ the fully paleoclimate-adjusted regional climate model COSMO-CLM over China on a 0.22° resolution. This model incorporates external forcings such as solar, orbital, volcanic, greenhouse gas, and land-use changes, aiming to reduce reliance on input from coarse-resolution General Circulation Models (GCMs). The goal is to produce simulations that better capture climate changes over the past 2000 years at the regional scale. Focusing on specific periods during the Little Ice Age and major tropical volcanic eruptions, we compare our model results with climate reconstructions from various regions in China. The COSMO-CLM successfully reproduces the impact of volcanic eruptions on China's climate, particularly regarding temperature changes. However, the intricate topography introduces complexities that affect the regional model's performance, leading to notable differences compared to other reconstructions, along with inherent uncertainties in the results.

The climate of the eastern Mediterranean and the Middle East is well documented in natural (speleothems, tree rings, sediments and pollen) and human-historical archives. The 6th century CE is of particular interest from both a historical and climatic perspective. It is a period of prosperity for the Eastern Byzantine Empire and political stability, but also a time when there was a heavily debated plague pandemic and significant climate variability associated with a major cluster of volcanic eruptions. Dynamical downscaling can bridge the gap between palaeo-records and climate reconstructions, which can be affected by various sources of uncertainty, and the coarsely resolved Earth System Models (ESMs) with 200 km or more horizontal resolution. A transient paleo-simulation with the appropriately adjusted regional climate model COSMO-CLM (CCLM, COSMO 5.0 clm16) is carried out to investigate possible links and feedbacks between the socio-political and economic conditions and the climate variability of that period in more detail.The state-of-the-art and CMIP6 compliant forcing reconstructions of volcanic (stratospheric aerosol optical depth), orbital (eccentricity, obliquity, precession), solar (irradiance), land-use and greenhouse-gas changes used for the MPI-ESM-LR (Jungclaus et al. 2017) are therefore implemented in the regional climate model. The simulated temperature and precipitation are compared with those of other CMIP6 models as well as with proxy records and reconstructions. In connection with the two successive volcanic eruptions in 536 and 540 CE, the annual temperature of the entire region dropped noticeably until about 550 CE. The signal for precipitation is not as clear, but the years of the eruptions are the driest of the century in the eastern Sahara and Arabian Peninsula and the wettest in the eastern Mediterranean.

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 degrees 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.

The Eastern Mediterranean and Middle East region is influenced by multiple large-scale atmospheric circulation patterns including the Indian Summer Monsoon the North Atlantic Oscillation (NAO), the East Atlantic / Western Russia and Scandinavian patterns. The area offers a broad spectrum, both in time and space, of long high-quality instrumental time series, documentary information and natural archives. Yet, recent reviews revealed that paleoclimate modelling with low horizontal resolution cannot fully help to understand the interactions of the multiple atmospheric patterns, the Mediterranean SSTs and connect potential climate impacts that may trigger or contribute to major social-historical events. Thus, there is a need to integrate high-resolution regional climate modelling into paleo applications. Furthermore, such integration will close the gap between the coarse resolution of climate models and the regional to local scale that is covered by the proxy and historical evidence and will enable a better data-model comparison. We use the regional climate model COSMO-CLM (CCLM) in an adjusted (orbital, solar and volcanic forcing, greenhouse gas concentrations and land-use changes) paleoclimate version. Simulations are performed with 0.44° and 0.11° spatial resolution on a domain including the Eastern Mediterranean and the Middle East in time slices of the past 2000 years. Simulations of the present (1979-2019) with this paleoclimate version of CCLM forced by ERA-Interim reanalysis data have shown promising results compared to observational and reanalysis data sets. The mean annual cycles of precipitation and temperature of the Mediterranean are correctly shown with high temperatures and low precipitation during the summer months and lower temperatures and higher precipitation during the winter months. Additionally, the effect of climate change is simulated with increasing temperatures during the last 40 years. Simulations of the present (1979-2019) and past periods (525-575 CE and 1220-1290 CE) forced by the MPI-ESM-LR ‘past2k’ simulations performed under the CMIP6 protocol will be performed at the next step and first results will be shown in the frame of this conference. The periods are chosen because of high volcanic activity and to study the volcanic influence on climate. Those results are going to be used to link historical events with the regional climate and contribute to a better understanding of the indirect and complex association between climate and society.

<p>The interactions and feedbacks between climate stress and social systems are currently the focus of interest for the scientific community and the general public. Understanding how paleo societies responded to extreme climate conditions is important for gaining insight into current and future climate concerns. The East Mediterranean (EM) and the Nile River basin (NR) are ideal areas for scientific and historical studies and modelling experiments due to the abundance of proxy and historical data. The 6<sup>th</sup> century AD is of particular interest from both a historical and scientific perspective, as it coincides with a period of prosperity for the Eastern Byzantine Empire and political stability, but which also experienced a plague pandemic and significant climate variability in parallel or as a result of a major cluster of volcanic eruptions. To investigate these events and the climate variability in the 6th century in more detail, a transient paleo-simulation is carried out with the appropriately adjusted regional climate model COSMO-CLM (COSMO 5.0 clm16). The regional climate model is driven by the global MPI-ESM-LR at 0.44° for the last 2500 years. The state-of-the-art external forcings of the CMIP6 compliant Earth System Model comprise of volcanic (stratospheric aerosol optical depth), orbital (eccentricity, obliquity, longitude), solar (irradiance), land-use (leaf area index and plant coverage) and greenhouse-gas (CO2 equivalent) changes, implemented in the regional climate model. The simulated temperature and precipitation will be compared with those of other CMIP6 models, and proxy records. This research will provide a comprehensive interpretation of the regional climate and its impacts during the 6th century AD in the Mediterranean.</p> <p> </p> <p>Reference</p> <p>Jungclaus, J. H., Bard, E., Baroni, M., Braconnot, P., Cao, J., Chini, L. P., Egorova, T., Evans, M., González-Rouco, J. F., Goosse, H., Hurtt, G. C., Joos, F., Kaplan, J. O., Khodri, M., Klein Goldewijk, K., Krivova, N., LeGrande, A. N., Lorenz, S. J., Luterbacher, J., Man, W., Maycock, A. C., Meinshausen, M., Moberg, A., Muscheler, R., Nehrbass-Ahles, C., Otto-Bliesner, B. I., Phipps, S. J., Pongratz, J., Rozanov, E., Schmidt, G. A., Schmidt, H., Schmutz, W., Schurer, A., Shapiro, A. I., Sigl, M., Smerdon, J. E., Solanki, S. K., Timmreck, C., Toohey, M., Usoskin, I. G., Wagner, S., Wu, C.-J., Yeo, K. L., Zanchettin, D., Zhang, Q., and Zorita, E.: The PMIP4 contribution to CMIP6 – Part 3: The last millennium, scientific objective, and experimental design for the PMIP4 <em>past1000</em> simulations, Geoscientific Model Development, 10, 4005–4033, https://doi.org/10.5194/gmd-10-4005-2017, 2017.</p>

Abstract. Understanding the past climate at regional scale, the impact of natural variability and sensitivity by studying the underlying dynamics and processes, can provide a point of reference for future climate conditions under anthropogenic forcing. The Eastern Mediterranean (EM) and Nile River basin (NR) regions are of particular interest for the study of past climate due to their location under the influence of major atmospheric teleconnections. We developed a high-resolution regional model for paleoclimate applications, COSMO-CLM, by integrating all external forcings and conducted a transient simulation from 500 BCE to 1850 CE. Principal Component Analysis (PCA) was applied for winter/summer precipitation and temperature to validate the model set up and showed very good agreement between simulated and observational/reanalysis data. Further, 400–362 BCE and 1800–1850 CE have been selected for the comparison of the mean climate conditions of the early Roman period (ERP) and pre-industrial times (PI). The comparison of temperature and precipitation suggests comparable mean climatic conditions with spatial differences in terms of variability within the study regions. Over the Eastern Mediterranean (EM), ERP is wetter and warmer in both winter and summer compared to PI, with higher variability in temperature and precipitation in summer than in winter. In the Nile River basin (NR), ERP summers were wetter and more variable compared to PI. The ERP over NR is warmer by approximately 0.5 °C in winter and cooler by 0.5 °C in summer, with low variability in winter and high variability in summer compared to PI. The relevant large-scale circulation of the two periods shows consistent spatial structures with the corresponding precipitation/temperature EOF patterns, albeit with varying amplitudes. The 2500 years transient simulation sheds light to the paleoclimate conditions and relevant atmospheric circulation as well as processes of periods of interest in complex areas with detailed output and comprehensive forcing allowing for better representation of the regional climate variability and change. Comparison of simulated output with proxy records, reconstructions and detailed studies of specific events, e.g., volcanic eruptions, can help to capture the spatiotemporal extent of these events and their impact on climate variability and change, in addition to providing insights into their impact on societal change and human history.

The project DAKI-FWS (BMWi joint-project “Data and AI-supported early warning system to stabilise the German economy”; German: “Daten- und KI-gestütztes Frühwarnsystem zur Stabilisierung der deutschen Wirtschaft”) develops an early warning system (EWS) to strengthen economic resilience in Germany. The EWS enables better characterization of the development and course of pandemics or hazardous climate extreme events and can thus protect and support lives, jobs, land and infrastructures. The weather and climate modules of the DAKI-FWS use state-of-the-art seasonal forecasts for Germany and apply innovative AI-approaches to prepare very high spatial resolution simulations. These are used for the climate-related practical applications of the project, such as pandemics or subtropical/tropical diseases, and contribute to the estimation of the outbreak and evolution of health crises. Further, the weather modules of the EWS objectively identify weather and climate extremes, such as heat waves, storms and droughts, as well as compound extremes from a large pool of key data sets. The innovative project work is complemented by the development and AI-enhancement of the European Flood Awareness System model, LISFLOOD, and forecasting system for Germany at very high spatial resolution. The model combined with the high-end output of the seasonal forecast prepares high-resolution, accurate flood risk assessment. The final output of the EWS and hazard maps not only support adaptation, but they also increase preparedness providing a time horizon of several months ahead, thus increasing the resilience of economic sectors to impacts of the ongoing anthropogenic climate change. The weather and climate modules of the EWS provide economic, political, and administrative decision-makers and the general public with evidence on the probability of occurrence, intensity and spatial and temporal extent of extreme events as well as with critical information during a disaster.

How did climatic and environmental variability and stress affect past societies in an area of increasing relevance for contemporary planning and policy concerns? The Eastern Mediterranean (EM) and the Nile river basin (Nile) bear a long history of human social dynamics, making it a suitable area for exploring potential interactions between climate variability, extreme events, environmental changes and society over a variety of time scales. The areas contain abundant natural and human-historical archives that preserve information on the climate conditions and impacts on humans and ecosystems covering the past centuries to millennia. So far, the links between climate and societies are examined mainly from the proxy records or the derived paleoclimatic reconstruction perspectives, without addressing the detail of the processes and underlying dynamics that offer the regional climate model simulations. In order to improve our understanding of past climate in the EM and Nile at the regional scale, we developed a spatially high resolved fully-forced paleoclimate version of the COSMO-CLM running over the past 2500 years. All forcings used for the driving ESM, namely volcanic (stratospheric aerosol optical depth), orbital (eccentricity, obliquity, precession), solar (irradiance), land-use and greenhouse-gas changes are implemented to COSMO 5.0-clm16 (see Hartmann et al. for more details). As a starting point for exploring the relationship between climate and society over the last 2500 years, we compared the mean climate conditions (2m temperature and precipitation) of two periods that are 2400 years apart, namely BCE 400-362 and 1980-2018 CE. Overall, the results show that summer temperatures differ by up to 3 degrees between the two periods. In particular, over the tropics, the temperature differences are largest. Precipitation changes vary within the study area and the climate regimes covered. We will further analyze the dynamics and climate variability of the area over the two periods to explore more details of regional and local climate change.

The climate of the last 2500 years is documented in natural (speleothems, tree rings, sediments and pollen) and human-historical archives. Proxy records and subsequent climate reconstructions can be subject to a considerable amount of uncertainty, as the proxies can only capture a fraction of the entire variability. Climate model simulations can contribute to the interpretation of variations observed in the paleoclimate data and better understanding of dynamics, mechanisms and procedures. The state-of-the-art simulations following the CMIP6-protocol are highly resolved in time but still present a rather coarse horizontal resolution (200 km or more) to adequately address regional paleoclimate questions/hypotheses. Dynamical downscaling can close the gap between the regional archives and the coarsely resolved Earth System Models (ESMs). Using regional climate models to downscale ESM output requires a consistent implementation of the climate forcings in the regional model used also for the driving ESM. State-of-the-art and CMIP6 compliant reconstructions of volcanic (stratospheric aerosol optical depth), orbital (eccentricity, obliquity, precession), solar (irradiance), land-use and greenhouse-gas changes used for the MPI-ESM are therefore implemented in the regional climate model COSMO-CLM (CCLM, COSMO 5.0 clm16). The functionality of each implemented forcing is tested separately and in combination for the period (1255-1265) that covers the Samalas volcanic eruption of 1257. The orbital forcing is found to have the largest impact in general and the volcanic forcing has a strong but short-lasting effect after the eruption. The other climate forcings only show very small impact in the chosen period. At the moment, a transient CCLM simulation with all forcings implemented with a horizontal resolution of 50 km is running for the last 2500 years in the Eastern Mediterranean, the Middle East and the Nile River basin.

The question of how sensitive the regional and local climates are to different land cover maps and fractions is important, as land cover affects the atmospheric circulation via its influence on heat, moisture, and momentum transfer, as well as the chemical composition of the atmosphere. In this study, we used three independent land cover data sets, GlobCover 2009, GLC2000 and ESACCI-LC, as the lower boundary of the regional climate model COSMO-CLM (Consortium for Small Scale Modeling in Climate Mode, v5.0-clm15) to perform convection-permitting regional climate simulations over the large part of Europe covering the years 1999 and 2000 at a 0.0275° horizontal resolution. We studied how the sensitivity of the impacts on regional and local climates is represented by different land cover maps and fractions, especially between warm (summer) and cold (winter) seasons. We show that the simulated regional climate is sensitive to different land cover maps and fractions. The simulated temperature and observational data are generally in good agreement, though with differences between the seasons. In comparison to winter, the summer simulations are more heterogeneous across the study region. The largest deviation is found for the alpine area (−3 to +3 °C), which might be among different reasons due to different classification systems in land cover maps and orographical aspects in the COSMO-CLM model. The leaf area index and plant cover also showed different responses based on various land cover types, especially over the area with high vegetation coverage. While relating the differences of land cover fractions and the COSMO-CLM simulation results (the leaf area index, and plant coverage) respectively, the differences in land cover fractions did not necessarily lead to corresponding bias in the simulation results. We finally provide a comparative analysis of how sensitive the simulation outputs (temperature, leaf area index, plant cover) are related to different land cover maps and fractions. The different regional representations of COSMO-CLM indicate that the soil moisture, atmospheric circulation, evaporative demand, elevation, and snow cover schemes need to be considered in the regional climate simulation with a high horizontal resolution.

The interaction between climate variability, extreme events and societies in the Eastern Mediterranean and the Middle East (EMME) and the Nile river basin is of particular interest in the last 2000 years. Major civilizations and complex pre-modern societies have written the greatest and multifaceted history of the area. However, the influence of climate on the societies is examined only from the proxy records perspective, without the detail of the processes that offer regional climate model simulations. The present and future climate and climate variability of this region are currently studied in the frame of the MENA CORDEX program with different global and regional climate models. For the past climate, exist only global climate or earth system model simulations with a coarse spatial resolution with a minimum of 100 km horizontal resolution. We aim at improving our understanding of past climate in the EMME and the Nile river basin (Nile) at the regional scale and use an adjusted paleoclimate version of the COSMO-CLM. Test simulations have been performed over the study region for the years 2017-2018 to identify the best settings of CCLM with respect to the CORDEX-MENA simulations which are carried out by Bucchignani et al. (2016). Test simulations show the CCLM can correctly simulate large tropical volcanic eruptions, as conditions similar to the Tambora eruption by adapting the stratospheric aerosol optical depth (AOD) mimicking conditions after a Tambora-like volcanic eruption. In agreement with Bucchignani et al. (2016), the albedo and aerosols parameters are found to be most important for the area and may be responsible for larger deviations compared to observational data. Thus, CCLM climate modelling for the present (1979-2019) and selected paleo-periods (525-575 CE and 1220-1290 CE) with intense volcanic activity will be forced by the MPI-ESM-LR ‘past2k’ simulation with the optimized settings which is identified in the test simulations. Orbital, solar and volcanic forcing, together with vegetation, land-use changes and greenhouse gas changes will be addressed step by step in the CCLM with resolutions of 0.44° and 0.11°. The present-day simulations show that the temperature and precipitation are well simulated compare to reanalysis and observational data in general. Additional, CCLM correctly captured convection and cloud cover clearly define the model performance in the greater southern areas of the domain that are affected by the tropical convection. Further, the orography and the land-sea interaction seem to significantly influence the local climate and may lead to differences compared to observations, which may also be strongly connected with the specific spatial resolution. For example, the Ethiopian Highlands and the East African Plateau have high elevations and have a large impact on the regional climate. Reference Bucchignani, E., Cattaneo, L., Panitz, HJ. et al. Sensitivity analysis with the regional climate model COSMO-CLM over the CORDEX-MENA domain. Meteorol Atmos Phys 128, 73–95 (2016). https://doi.org/10.1007/s00703-015-0403-3

Feedbacks of plant phenology to the regional climate system affect fluxes of energy, water, CO2, biogenic volatile organic compounds as well as canopy conductance, surface roughness length, and are influencing the seasonality of albedo. We performed simulations with the regional climate model COSMO-CLM (CCLM) at three locations in Germany covering the period 1999 to 2015 in order to study the sensitivity of grass phenology to different environmental conditions by implementing a new phenology module. We provide new evidence that the annually-recurring standard phenology of CCLM is improved by the new calculation of leaf area index (LAI) dependent upon surface temperature, day length, and water availability. Results with the new phenology implemented in the model show a significantly higher correlation with observations than simulations with the standard phenology. The interannual variability of LAI improves the representation of vegetation in years with extremely warm winter/spring (e.g., 2007) or extremely dry summer (e.g., 2003) and shows a more realistic growth period. The effect of the newly implemented phenology on atmospheric variables is small but tends to be positive. It should be used in future applications with an extension on more plant functional types.

Physikalische BlätterVolume 34, Issue 2 p. 100-100 AktuellesOpen Access Aktuelles/KKW Obrigheim lieferte 20 TWh First published: Februar 1978 https://doi.org/10.1002/phbl.19780340211AboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume34, Issue2Februar 1978Pages 100-100 RelatedInformation

13 Understanding the past climate at regional scale, the impact of natural variability and sensitivity by studying the 14 underlying dynamics and processes, can provide a point of reference for future climate conditions under anthropogenic 15 forcing. The Eastern Mediterranean (EM) and Nile River basin (NR) regions are of particular interest for the study of past 16 climate due to their location under the influence of major atmospheric teleconnections. We developed a high-resolution 17 regional model for paleoclimate applications, COSMO-CLM, by integrating all external forcings and conducted a 18 transient simulation from 500 BCE to 1850 CE. Principal Component Analysis (PCA) was applied for winter/summer 19 precipitation and temperature to validate the model set up and showed very good agreement between simulated and 20 observational/reanalysis data. Further, 400-362 BCE and 1800-1850 CE have been selected for the comparison of the 21 mean climate conditions of the early Roman period (ERP) and pre-industrial times (PI). The comparison of temperature 22 and precipitation suggests comparable mean climatic conditions with spatial differences in terms of variability within the 23 study regions. Over the Eastern Mediterranean (EM), ERP is wetter and warmer in both winter and summer compared to 24 PI, with higher variability in temperature and precipitation in summer than in winter. In the Nile River basin (NR), ERP 25 summers were wetter and more variable compared to PI. The ERP over NR is warmer by approximately 0.5 °C in winter 26 and cooler by 0.5 °C in summer, with low variability in winter and high variability in summer compared to PI. The 27 relevant large-scale circulation of the two periods shows consistent spatial structures with the corresponding 28 precipitation/temperature EOF patterns, albeit with varying amplitudes. The 2500 years transient simulation sheds light 29 to the paleo climate conditions and relevant atmospheric circulation as well as processes of periods of interest in complex 30 areas with detailed output and comprehensive forcing allowing for better representation of the regional climate variability 31 and change. Comparison of simulated output with proxy records, reconstructions and detailed studies of specific events, 32 e.g., volcanic eruptions, can help to capture the spatiotemporal extent of these events and their impact on climate 33 variability and change, in addition to providing insights into their impact on societal change and human history.