Orals: Mon, 4 May, 16:15–17:55 | Room 0.49/50
The field of historical climate reconstruction through documentary evidences has made significant advances in recent years, including a global synthesis of the index approach in climate reconstruction (Nash et al., 2021), a global documentary climate dataset (Burgdorf et al., 2023), and new perspectives to study historical climatology (White et al., 2022). Based on the progress, this study addresses two specific research questions: 1) What are the numerical structures and characteristics of the reconstructed climate index data across existing datasets from various continents? (2) Are these structures and characteristics reflective of long-term climatological traits in the regions, or are they controlled by other factors? By answering the questions, we collected climate index data from Africa, Australia, China, Europe, India and South America to analyze the data structure in each dataset. Each dataset’s structure was then compared against modern observational data, including ERA5 and the Global Historical Climatology Network (GHCN) monthly data, to identify correlations and asses credibility of the climate index data. The analysis involves spatial and temporal comparisons, statistical tests, and discussions on data quality and limitations.
How to cite: Lin, K.-H. E., Lin, Y.-H., Lee, J.-I., Nash, D., Grab, S., Adamson, G. C. D., Dobrovolný, P., Gergis, J., Nicholson, S. D., Norrgård, S., del Rosario Prieto, M., Tseng, W.-L., and Huang, H.-C.: A global synthesis of climate indices reconstructed from historical archives, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6141, https://doi.org/10.5194/egusphere-egu26-6141, 2026.
Extreme cold events have played a crucial role in shaping environmental conditions, agricultural productivity, and societal resilience across Europe; however, reconstructions for Central and Eastern Europe prior to the early modern period remain scarce. Establishing a long-term perspective on cold extremes is essential for understanding natural climate variability and contextualising recent climatic changes. This study presents the first systematic reconstruction of cold extremes in medieval Poland for the period 1000–1500 CE using documentary evidence.
A comprehensive database was developed from handwritten and unpublished sources, published documents, and secondary literature. Each record was critically evaluated and coded for event category, location, date, duration, intensity, source quality, and reported impacts. Four principal categories of cold extremes were identified: (1) severe frosts; (2) snow and snowstorms; (3) freezing of rivers, lakes, and the Baltic Sea; and (4) cold waves. The dataset allowed for the distinction of 135 severe frost events, 45 snow-related events, 90 ice-related events, and 65 cold waves, each classified using a three-tier intensity index (1: weak/moderate; 2: strong; 3: very strong or catastrophic).
Spatial attribution was performed for six major historical regions: Baltic Coast and Pomerania, Masuria–Podlasie, Greater Poland, Masovia, Silesia, and Lesser Poland, with an additional category (Poland) for events lacking a precise location. The results show a clear geographical imbalance in documentary coverage: the Baltic Coast and Pomerania region accounts for 49.71% of all identified weather notes, likely reflecting the larger number of preserved documentary sources from this area. Although a much larger number of weather notes originally existed, repeated descriptions of the same event were removed, and only the most reliable and independent sources were retained in the final database. This methodological refinement ensures that the reconstructed patterns accurately reflect genuine climatic signals, rather than merely reflecting documentary redundancy.
Intensity analysis shows that very strong and catastrophic events constitute 46.28% of all cases, making them the most frequently documented category in the medieval sources. Strong events constitute 32.28%, while weak and moderate events are the least common, accounting for 21.42%. Many of these extreme events describe multi-week or multi-month cold episodes, allowing for detailed assessments of temporal persistence and severity.
Reported impacts include human and animal mortality, crop failure and famine, infrastructure damage, effects on transportation and trade, economic losses, political consequences, and environmental disturbances. These findings highlight both the climatic and socio-economic significance of cold extremes and demonstrate the value of documentary evidence for reconstructing high-resolution regional climate variability over multi-centennial timescales.
This reconstruction provides a new empirical foundation for comparing medieval cold extremes with modern climatological records, supports model–data comparison exercises, and contributes to broader efforts to interpret past climate variability across Central Europe.
This work was supported by the National Science Centre, Poland, project No. 2020/37/B/ST10/00710.
How to cite: Akbari Moghaddam Sani, S., Przybylak, R., and Oliński, P.: Reconstructing Cold Extremes in Medieval Poland (11th–15th Centuries) from Documentary Evidence, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-335, https://doi.org/10.5194/egusphere-egu26-335, 2026.
There is growing concern that ongoing climate change is altering the frequency and magnitude of river floods. However, the lack of long-term observational time series of flood events makes verification difficult, particularly in the Mediterranean region, where complex orography produces strong sub-regional variability. Because available instrumental discharge records are too short to identify low- and high-frequency periodicities and to disentangle climatic and anthropogenic forcings, it is necessary to integrate measured data with non-systematic hydrological information derived from historical documents, archaeological evidence, and sedimentary proxies. Here we present the reconstruction and analysis of floods of the Arno and Serchio rivers, located in a key area of the Mediterranean Basin, based on archaeological and historical sources. Both rivers are well known for their destructive floods affecting the cities of Lucca, Pisa, and Florence. The earliest historically documented flood dates to 217 BCE. Phases of increased flood occurrence are identified during the early Roman period (1st–2nd centuries BCE) for the Serchio River, while enhanced flood activity affecting both rivers is observed during the Late Antique Little Ice Age. In addition, a new flood record for the Arno River since the 12th century CE was developed using an automated methodology for the analysis of written sources. The reconstructed series allows the identification of several flood-rich phases in the Arno basin, some of which broadly coincide with periods of reduced solar activity previously recognized in other Italian rivers. In contrast, correlations with reconstructed North Atlantic Oscillation indices appear variable and dependent on the selected index and time lag. Overall, these results emphasize the importance of long-term archaeological and historical records for providing a broader context to recent flood variability and for improving the interpretation of flood patterns in Mediterranean river systems.
How to cite: Bini, M., Zanchetta, G., Luppichini, M., Lazzarotti, M., Fabiani, F., and Fornaciari, A.: Two Millennia of Floods in a Key Area of the Mediterranean Basin Documented by Archaeological and Historical Sources: Climatic Implications and Future Perspectives, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17356, https://doi.org/10.5194/egusphere-egu26-17356, 2026.
The North Pacific is a critical component of the global climate system, yet high-resolution quantitative temperature records for the past millennium from this region remain scarce, limiting our understanding of its natural variability and response to forcing factors. This study presents an annually resolved paleotemperature reconstruction for the Kamchatka Peninsula spanning the last 1200 years, based on a calibrated bromine (Br) proxy derived from maar lake sediments.
Synchrotron radiation X-ray fluorescence (SR-XRF) has been used for nondestructive in situ analysis of elements on a precisely dated sediment core from Lake Chasha. Br in lacustrine systems is strongly associated with organic matter through covalent C-Br bonds, and its sedimentary concentration is fundamentally regulated by temperature-dependent primary productivity and terrestrial organic matter flux in this cold region. For the modern period (1989-2020), the Br record shows a strong and statistically significant positive correlation (r=0.72, p<0.001) with instrumental summer air temperature from a nearby meteorological station, validating its use as a quantitative paleothermometer.
The resulting Br-derived temperature record robustly captures the major climatic epochs of the Common Era: the Dark Ages Cold Period (DACP, ~5th–8th centuries), the Medieval Climate Anomaly (MCA, ~9th–13th centuries), and the Little Ice Age (LIA, ~14th–19th centuries). The 20th-century warming signal is unprecedented in amplitude over the entire 1200-year period. Spectral analysis reveals significant periodicities at ~88,10-11 years and 3-4 years. Visual comparison and coherence analysis indicate that multi-decadal to centennial-scale variability in the record is modulated by both internal climate dynamics, showing an anti-correlation with Pacific Decadal Oscillation (PDO) phases, and external solar forcing, with notable correspondence to major solar minima (e.g., Maunder Minimum).
Our result provides a high-resolution benchmark for the North Pacific, significantly improving our capacity to characterize natural climate variability, evaluate climate models, and decipher the regional interplay between internal ocean-atmosphere oscillations.
How to cite: Novikov, V., Wu, J., Chu, G., and Darin, A.: A high-resolution 1200-year bromine-based paleotemperature record from Maar Lake Chasha (Kamchatka Peninsula), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-918, https://doi.org/10.5194/egusphere-egu26-918, 2026.
We present the first tree-ring based summer surface temperature reconstruction (1382-2017) for the Southern Hemisphere that expresses strong volcanically forced cooling. The Northern Patagonia (NPAT) reconstruction is based on RW and Blue Intensity (BI) parameters measured from Araucaria araucana trees from 6 locations across the middle to southern end of the species’ range in Argentina. This multi-TR-parameter reconstruction explains 53% of the summer surface temperature variance (1903-2017), which is on par with the fidelity of TR based reconstructions from the Northern Hemisphere. The reconstruction coheres strongly with surface mean air temperatures for a large region in South America including sea surface temperatures well into the southeastern Pacific for these latitudes. The warmest 10-year period is 2008-2017, corresponding to the last ten years of the reconstruction, while the coldest period is 1455-1464. The coldest reconstructed year is 1971, followed by 1460. For both the NPAT reconstruction and a range of model simulations, superposed epoch analysis, using major tropical eruptions since the 1400s, indicates a significant post-eruption mean surface cooling of ca. 0.4 - 1.0 oC, depending on which volcanic events are used. The degree of relative cooling is on par, or even stronger, with the cooling represented by individual TR records used in the Northern Hemisphere N-TREND database suggesting that the volcanic response in northern Patagonia over the last 6 centuries is equivalent, or even more extreme, to what is observed in many Northern Hemisphere locations. Our results indicate that the use of ring-density parameters is of paramount importance for assessing past volcanically forced cooling in the Southern Hemisphere, but the dating and seasonality of the eruptions as well as the continentality and mid-latitude location of the woodland sites may also be important factors for capturing the signal of volcanic cooling.
How to cite: Wilson, R., Mundo, I., Marshal, L., Reid, E., Sigl, M., Schmidt, A., Timmreck, C., Fang, S.-W., Abernethy, R., Daux, V., and Villalba, R.: Tree-ring reconstruction of summer temperatures in Northern Patagonia reveals significant cooling following large-magnitude explosive volcanic eruptions in the tropics, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4403, https://doi.org/10.5194/egusphere-egu26-4403, 2026.
Climate variability over the last two millennia (Past2k) reflects the combined influence of internal climate dynamics, including modes such as ENSO, external forcings such as volcanic and solar activity, and, in recent centuries, increasing anthropogenic forcing. Studying the Past2k period provides critical context for understanding current and future climate change in a warming world. In the pre-instrumental era, the absence of direct climate observations necessitated reliance on climate models and paleoclimate archives to infer past climate conditions.
Paleoclimate data assimilation (PDA) is an effective approach to integrate the information from both climate models and natural proxies. Here, we employ an offline PDA framework to generate a new spatiotemporally resolved global reconstruction of the Past2k at annual and seasonal (summer and winter) resolution, including key climate fields (e.g., temperature, pressure, precipitation), drought indices (scPDSI, SPEI), and climate indices (e.g., ENSO, PDO, AO).Proxy observations are compiled from the Iso2k, PAGES2k, CoralHydro2k, and SISALv3 databases, together with additional tree-ring width datasets. The model priors are derived from isotope-enabled Earth system model simulations using MPI-ESM-wiso and iCESM.
Relative to previous global reconstructions, this assimilation framework advances PDA by explicitly assimilating isotopic proxy records, employing physically based proxy system models, accounting for proxy seasonality and climate sensitivity, and incorporating low-resolution records across multiple timescales. We conducted comprehensive evaluations of the reconstructed fields and indices against instrumental/reanalysis datasets, as well as existing global PDA-based reconstructions, and also assessed the reconstruction skill in earlier centuries. These evaluations show that our reconstructions perform well and yield reliable results. We expect that our datasets will provide a millennial-scale climate context to support further studies of past climate variability and to inform analyses of ongoing and future climate change.
How to cite: Cheng, J., Cauquoin, A., Okazaki, A., Truax, O., Sinha, A., Li, H., Li, S., and Yoshimura, K.: A New Dataset of Global Climate and Hydroclimate Reconstructions over the Common Era, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18416, https://doi.org/10.5194/egusphere-egu26-18416, 2026.
Drought variability over the last millennium remains poorly understood in a global context--reflecting the sparsity of instrumental records and reconstructions from paleoclimatic proxies. Yet, a quantification of the long-term forced and unforced variability of droughts across regions globally is key for assessing the extremeness of currently observed drought events. Here, we use 20 ensemble members from a 600-year ensemble simulation (ModE-Sim, 1420 - 2009) and modern reanalysis data (ERA5-Land, 1950-2024) to place recent drought extremes in a multi-century historical context. For measuring drought magnitude and timing, we consider the annual maximum potential cumulative water deficit (PCWD)--a physically and ecologically-grounded metric, integrating atmospheric moisture demand and supply and the relative timing of daily precipitation, snow melt, and radiation. To investigate changes over the simulated period, we assess trends, low-frequency variability, and effects of external forcing. Our results show that internal hydroclimate variability differs across regions and can be of the same magnitude as forced events. Towards the modern era (2000-2024), PCWD exceeds the reference (1420-1969) with unprecedentedly high values in 13 out of 43 regions. Despite modern droughts not being unprecedented in most regions when considering a 600 year reference and unforced variability across 20 ensemble members, our results show that the statistics of droughts are widely shifting. Moderate (5-year) drought extreme events have at least doubled in frequency in modern times in 20 out of 43 land regions. The severity of modern severe (30-year) drought extreme events is unprecedented in 36 out of 43 regions with respect to the last 600 years. Depending on the reference period chosen to characterize modern extremes, the affected region and total number of regions with unprecedented annual record PCWD differs strongly. This study highlights a fundamental transformation in drought regimes, which is unprecedented over the past 600 years for a large fraction of global land regions, even as unprecedentedly strong droughts have been recorded to date in only about a quarter of regions globally. This highlights the importance of reference period and metric selection in characterizing modern extremes. Taken together, our findings demonstrate that modern droughts are not only more intense, but also more frequent than those of the preindustrial past in most regions globally. However, in many regions, drought extremes in the reanalysis period do not yet exceed the most severe events simulated across ensemble members over the past 600 years.
How to cite: Helpap, P., Brönniman, S., Hand, R., Franke, J., and Stocker, B. D.: Are modern droughts unprecedented?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2598, https://doi.org/10.5194/egusphere-egu26-2598, 2026.
Permafrost, a defining feature of high-latitude landscapes, has been rapidly degrading in recent decades due to ongoing global warming. One of the clearest indicators of this degradation is the loss of permafrost area. While recent retreat is well documented, few studies have placed changes of permafrost extent in the context of pre-industrial natural variability. Here we show, using multiple simulations from the Paleoclimate Model Intercomparison Project Phase 3 (PMIP3) and 4 (PMIP4), reanalyses, and reconstruction products spanning the full or part of the Common Era that the recent permafrost retreat is very likely unprecedented in the last 2,000 years. Across datasets, we estimate a permafrost area decrease of 0.7 to 2.5 million km², with the largest losses occurring along the southern margins of discontinuous permafrost. These regions are found to hold between 43 and 138 PgC of soil organic carbon, now vulnerable to potential microbial decomposition. The resulting carbon emissions could have already amplified global warming by 0.2 ºC, with implications for the pan-Arctic environment and the stability of global climate. This work highlights the value of ESM simulations for assessing permafrost variability over the Common Era, especially when interpreted alongside proxy-based paleoclimate reconstructions.
How to cite: García-Pereira, F., González-Rouco, J. F., and Meabe-Yanguas, N.: Recent permafrost retreat is very likely unprecedented in the Common Era, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6545, https://doi.org/10.5194/egusphere-egu26-6545, 2026.
The Atlantic Meridional Overturning Circulation (AMOC) is a key modulator of global climate and constitutes one of the tipping point elements in the context of anthropogenic climate change. Recent studies have identified an ongoing AMOC slowdown, potentially leading to a collapse which would have substantial climatic and societal impacts. However, the shortness of instrumental record is too limited to capture the full variability of the AMOC, and to delineate the contribution of internal variability from the impact of anthropogenic climate change. In this study, we attempt to put recent AMOC changes in a long-term context by assessing its variability over the past 2000 years. To this end, we compile marine proxy reconstructions from the North Atlantic to identify coherent signals over periods of known climatic perturbations such as the Roman Warm Period, the Medieval Warm Period and the Little Ice Age and to determine their potential relationship with the AMOC state. Further, we compare these reconstructions with outputs from a transient numerical simulation over 1700-2023 AD run with the NEMO – SI3 global ocean-sea ice model, forced by a paleo-based atmospheric reconstruction, to identify ocean circulation changes across the termination of the Little Ice Age and under modern global warming.
How to cite: Tiwari, S., Goosse, H., Dalaiden, Q., and de Vernal, A.: AMOC changes over the past 2000 years: insights from marine proxy records and a simulation with a sea-ice-ocean model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15884, https://doi.org/10.5194/egusphere-egu26-15884, 2026.
The Max Planck Institute for Meteorology Earth System Model (MPI-ESM) is used to produce an ensemble of simulations of the Common Era (CE) and several climate change scenarios until 2300 CE. The ensemble of simulations uses the standard version of the MPI-ESM (MPI-ESM1.2-LR) and a variant that includes developments in the hydrology and thermodynamics of its land surface model, JSBACH, particularly over permafrost areas: the Permafrost Physics Ensemble (MPIESM-PePE). Five members of the ensemble extend back to 0 CE under reference PMIP4/CMIP6 forcing specifications.
Subsurface hydro-thermodynamic processes have been modified to allow for exploring uncertainties related to the land model depth and to Arctic climate, specifically Arctic hydrology. Different vertical discretizations of JSBACH, including changes in its depth, are considered to modify the thermodynamic configuration of the model. JSBACH was modified to also include soil moisture phase changes with freezing-thaw conditions and other hydrological features, like an organic topsoil layer; dynamic soil thermal properties, or the implementation of a simple wetland and a new multi-layer snow scheme. These hydrological changes result in three contrasting model configurations: one stemming from the use of the standard model and two different set ups, including the previous improvements, in which the Arctic becomes comparatively wetter or drier.
Changes in a wetter or drier Arctic hydrology feedback to change Arctic temperatures and Arctic Amplification within periods of warming/cooling and thereby influencing Northern Hemispheric circulation. Changes in land depth influence the subsurface thermal state, with implications for land energy storage and permafrost. The MPIESM-PePe ensemble allows for exploring sensitivity to these changes in multi-centennial to millennial timescales. Some examples of model-data comparison will be provided.
How to cite: González-Rouco, F., García-Pereira, F., Meabe-Yanguas, N., Martínez-Vila, Á., Jungclaus, J., Hagemann, S., Lorenz, S., De Vrese, P., Cuesta-Valero, F. J., García-García, A., Beltrami, H., García-Bustamante, E., Navarro, J., Huang, R., Smerdon, J., and Tejedor, E.: Simulating the Common Era and climate change scenarios with the MPI-ESM: opportunities for model-data comparison, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19068, https://doi.org/10.5194/egusphere-egu26-19068, 2026.
The contemporary warming currently being observed on Earth is most intense in the Arctic and Sub-Arctic. Until the mid-20th century, human impact on the Arctic environment and climate was small, so it is extremely important to maximally understand these past conditions in order to better understand current and future changes.
To date, there has been little work based on climate data from Labrador dating back to the 19th century. In the case of bioclimatic studies, even fewer such works exist. In order to fill this gap, the following analyses were performed.
Changes in bioclimatic conditions in the north-eastern Labrador Peninsula were estimated based on two series of measurements. The first includes six years of meteorological observations from six measurement stations: Hebron, Hoffenthal, Nain, Okak Rama, and Zoar. The second series is based on data from the Hebron and Nain stations and covers nearly 50 years of data. Moravian missionaries conducted the meteorological measurements on behalf of the Deutsche Seewarte (German Society for the Protection of Climate). Contemporary data for comparison were obtained from the Canadian Centre for Climate Services and cover the years 1991–2020.
Deutsche Seewarte Hamburg provided the stations with tested and calibrated measuring instruments. Meteorological observations were carried out in accordance with the standardised Seewarte guidelines. These data were digitalised and made available by Deutscher Wetterdienst (DWD).
During the observations, measurements were taken of, among others, air temperature, atmospheric pressure and wind speed and direction. They were taken daily at three measurement times: 8:00, 14:00 and 20:00. Based on these data, bioclimatic analyses of selected bioclimatic indices were performed: Wind Chill Temperature (WCT) and Insulation Predicted (Iclp).
The data presented included the monthly mean values of selected parameters and their year-to-year changes. The frequencies of individual categories of meteorological conditions were determined based on the analysed bioclimatic indices. The results were compared with values obtained at other stations and compared to the conditions currently prevailing on the peninsula.
Based on the analyses conducted, it appears that, during the historical period, the average annual air temperature was lower, but wind speeds were also lower. Differences in bioclimatic conditions between the stadia are small, but conditions are least favourable in the north of the peninsula, whereas they are most favourable in the south.
The work was supported by the National Science Centre, Poland project No. 2020/39/B/ST10/00653.
How to cite: Chmist, K., Araźny, A., Przybylak, R., Wyszyński, P., and Singh, G.: Changes in bioclimatic conditions on the coast of the Labrador Peninsula from the end of the 19th century to the mid-20th century, compared to the contemporary period, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-605, https://doi.org/10.5194/egusphere-egu26-605, 2026.
This study examines the long-term thermal conditions in Nain, located on the coast of Labrador, and their changes by utilising all available sub-daily meteorological observations from the Arctic. Systematic weather recording began in 1771, when Moravian missionaries established a station among Inuit communities in the region now known as Nunatsiavut. They conducted measurements until 1939, although these were likely not continuous throughout the entire period. The long-term series of sub-daily air temperatures is available for the following intervals: 1771–1786, 1882–1913, and 1926–1938. For comparison, we also include a recent period of temperature data from 1990 to 2020. Thus, the analysis focuses on four periods representing important climatic phases: the Late Little Ice Age (LIA, 1771–1786), the Transitional Period (TP, 1882–1913) from the LIA to the Early Twentieth-Century Warming (ETCW), the mature phase of the ETCW (1926–1938), and the Contemporary Warming (CP, 1990–2020).
All sub-daily temperature data (recorded two to four times per day during the first period and at higher frequencies in later periods) were digitised, converted to modern Celsius units, and subjected to quality control. Mean daily air temperatures (MDATs) were calculated from the prepared sub-daily readings using a simple arithmetic mean. Next, MDATs were corrected to the so-called real daily mean using adjustment functions derived from contemporary hourly observations (1991–2010). These corrected MDAT values were then used to compute monthly, seasonal, and annual averages, as well as day-to-day temperature variability and thermal indices, including growing degree days (GDD), positive degree days (PDD), the air thawing index (ATI), and freezing degree days (FDI).
Preliminary analysis shows that the first two periods were the coldest, particularly the TP, with a mean annual temperature of -4.9°C. The winter temperature averaged -19.3 °C, while the summer temperature averaged 7.2 °C. In contrast, warming began with the onset of the ETCW, although it was clearly weaker than during the CP. In the most recent period, the mean annual, winter, and summer temperatures were -2.3°C, -15.4°C, and 9.3°C, respectively. From the late 18th century to the present, air temperature in Nain has increased by approximately 4 °C in winter and 2 °C in summer, while the annual temperature has risen by 2.6 °C. Other analysed characteristics (e.g., the frequency of MDATs in 1-degree intervals) show a significant decrease in cold events and an increase in warm events after the ETCW period.
The work was supported by the National Science Centre, Poland, project No. 2020/39/B/ST10/00653.
How to cite: Singh, G., Przybylak, R., Araźny, A., Wyszyński, P., and Chmist, K.: Thermal conditions in Nain (Labrador) from the late 18th century to the Second World War based on Moravian missionaries’ observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-649, https://doi.org/10.5194/egusphere-egu26-649, 2026.
Frequent rainstorm events in North China pose significant threats to both natural ecosystems and socio-economic systems. Based on historical documents including local gazetteers and archives, combined with instrumental records since the Republican era, this study systematically reconstructs the chronology of rainstorm events, extreme rainstorm sequences, and typhoon-induced rainstorm sequences in North China from 1368 to 2024, and further analyzes their spatiotemporal evolution patterns and driving mechanisms. First, following the principle of uniformitarianism, identification criteria for historical rainstorm events were established and validated through comparison with modern instrumental records. The reconstructed rainstorm chronology reveals significant variations across interannual, interdecadal, intra-annual, and spatial scales. Second, using the percentile threshold method, extreme rainstorm event clusters with a 30% occurrence probability from 1470 to 2024 were extracted. Further analysis indicates distinct spatial distributions of extreme rainstorms between cold and warm periods: during cold periods, rainstorm locations shifted northward and westward, primarily concentrated on the windward slopes of the Yanshan and Taihang Mountains. Extreme rainstorm events show positive correlation with typhoon frequency and exhibit significantly higher occurrence probability during La Niña decay years compared to El Niño decay years. Finally, based on identification methods for typhoon-induced rainstorms, typhoon rainstorm event clusters were further extracted. The study finds higher frequency of typhoon rainstorms during warm periods, with increased occurrence in relatively dry years. Unlike extreme rainstorms, typhoon rainstorms show similar occurrence probability during La Niña years and subsequent years, suggesting different driving mechanisms. This research reveals the evolutionary characteristics of rainstorm events in North China across different temporal scales and climatic backgrounds, providing scientific basis for understanding their formation mechanisms and for disaster prevention and mitigation.
How to cite: Liu, W. and Yang, Y.: Reconstruction and Analysis of Heavy Rainfall /Rainstorm Events in Northern China over the Past 650 Years, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-806, https://doi.org/10.5194/egusphere-egu26-806, 2026.
An integrated hybrid ensemble Kalman smoother (IHEnKS) is proposed to optimally utilize proxy data from the past to the future for paleoclimate data assimilation (PDA). As an extension of the integrated hybrid ensemble Kalman filter (IHEnKF), IHEnKS assimilates future proxies through cross-time error covariances, which are estimated from an online PDA by use of a deep learning-based surrogate model. To mitigate the influences of sampling errors and model errors, an adaptively estimated covariance localization varying with spatial and temporal separations is adopted to eliminate the sampling errors in space and time. Moreover, a hybridization with climatological cross-time error covariances through augmentation of lagged climatological perturbations are implemented. Consistent results are obtained from reconstructions of surface air temperature and sea surface temperature in both pseudoproxy and real proxy experiments. IHEnKS with spatial and temporal localizations and hybridization achieves the best reconstructions compared to various configurations of ensemble-based assimilation methods. The advantages of IHEnKS become more pronounced as the proxy network becomes sparser.
How to cite: Sun, H., Lei, L., Tan, Z., Ning, L., and Liu, Z.: An Ensemble Kalman Smoother for Online Paleoclimate Data Assimilation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2226, https://doi.org/10.5194/egusphere-egu26-2226, 2026.
Here we present one of the most comprehensive high-quality datasets of 19th century harvests in all of Europe—consisting of harvest yield ratio series of all the main crops from all 24 counties in Sweden during the period 1818–1870. Hierarchical cluster analysis reveals that a distinct regional structure in harvest variations, with coherent regions in northern, central-eastern, central-western, south-eastern, and south-western Sweden. However, the largest difference is that between the five northernmost counties and the rest of Sweden, reflecting the division into a growing season-temperature constrained agrometeorological zone in northern Sweden (approximately two-thirds of Sweden by area) and a corresponding zone based on the remaining regions in southern Sweden mainly dependent on summer soil moisture availability. Adjusting the harvest data by grain quality (weight) shows how variations in quality mainly mattered for northern of Sweden, where accounting for quality significantly increased the coefficient of variation.
Harvest yields of spring-sown crops (oats, barley, mixed-grain, legumes) were negatively correlated with mean June–August temperatures and positively associated with summer precipitation in the central-eastern, central-western, south-eastern and south-western Sweden, whereas harvest yields of all crops in northern of Sweden benefitted from warm springs and summers. These agrometeorological dependencies of spring crops are consistent with various other studies covering different periods from the late 17th century to the early 21st century (Edvinsson et al. 2009; Skoglund 2022, 2023, 2024; Ljungqvist et al. 2023; Sjulgård et al. 2023; Skoglund & Ljungqvist, 2026, in revision). Winter wheat yields were positively correlated with mean January–April temperatures in central-eastern Sweden, whereas harvest yields of winter cereals in the south-western and south-eastern Sweden shows a closer positive association with temperatures during and after sowing in the preceding August–October. Potato yields show a positive correlation with mean May–July temperatures in all of Sweden except the counties in the south bordering the Baltic Sea.
References
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Skoglund, M. K.: Climate variability and grain production in Scania, 1702–1911, Climate of the Past, 18, 405–433, 2022.
Skoglund, M. K.: Farming at the margin: climatic impacts on harvest yields and agricultural practices in central Scandinavia, c. 1560–1920, Agricultural History Review, 71, 203–233, 2023.
Skoglund, M. K.: The impact of drought on northern European pre-industrial agriculture, The Holocene, 34, 120–135, 2024.
Sjulgård, H., Keller, T., Garland, G., and Colombi, T.: Relationships between weather and yield anomalies vary with crop type and latitude in Sweden. Agricultural Systems, 211, 103757, 2023.
Skoglund, M.K. and Ljungqvist, F.C.: Climatic effects on grain harvest variations across Sweden c.1665–1810. Geografiska Annaler A: Physical Geography, in revision, 2026.
How to cite: Skoglund, M., Charpentier Ljungqvist, F., and Edvinsson, R.: Regional climate–harvest relationships in Sweden 1818–1870, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18860, https://doi.org/10.5194/egusphere-egu26-18860, 2026.
European summer hydroclimate has shifted markedly in recent decades, including widespread drying across many regions. However, major uncertainties remain regarding their spatiotemporal variability and underlying drivers. Here, we present the European Last Millennial Data Assimilation (EULMDA), a new reconstruction of European hydroclimate and its main drivers over the past millennium. EULMDA combines five Earth System Model simulations with more than 100 tree-ring records sensitive to moisture and temperature, and shows strong skill in reproducing instrumental variability in multiple climate fields, including large-scale circulation changes. For the warm season, we identify two dominant controls on European drought variability: circulation fluctuations linked to the Scandinavian pattern (SCAND) and long-term summer temperature changes. Together, these factors account for more than half of the spatiotemporal drought variance. The SCAND drives a pronounced north–south dipole in summer hydroclimate, explaining a larger fraction of Mediterranean drought variability than other major circulation modes, contributing to recent multidecadal drying in the Mediterranean alongside wetting in northern Europe. Meanwhile, summer warming intensifies drying across much of Europe. Taken together, these dynamic and thermodynamic processes have shaped European hydroclimate throughout the past millennium, providing critical context for interpreting recent drought trends and insight into mechanisms shaping future hydroclimate risks.
How to cite: Xue, H., Goosse, H., Dalaiden, Q., Seftigen, K., Gennaretti, F., and Shi, F.: Scandinavian pattern and temperature changes govern European summer droughts over the past millennium, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2317, https://doi.org/10.5194/egusphere-egu26-2317, 2026.
The North Atlantic Oscillation (NAO) is primarily a boreal winter climate phenomenon defined by fluctuations in atmospheric pressure between the Bermuda-Azores High and the Icelandic Low. The NAO is often characterized by a distinct tripole pattern of sea surface temperature (SST) anomalies across the North Atlantic, and significantly influences temperature and precipitation patterns, with far-reaching environmental and socioeconomic impacts. Previous studies on the NAO from paleo-archives and instrumental records reveal that the long-term variance of the NAO has been increasing since the 1800s, suggesting changes in its long-term behavior. However, our understanding of the NAO remains limited by short instrumental records. Moreover, most marine-based NAO reconstructions are in high-latitude or subtropical regions, or outside the Atlantic basin. Thus, highlighting the need for additional marine-based records from the tropical Atlantic. Here, we present a high-resolution 185-year Sr/Ca-based boreal winter (DJFM) SST reconstruction (1831-2015) in the western tropical North Atlantic from a massive Colpophyllia natans coral collected at Kelleston Drain, Tobago. We found that the coral-derived DJFM SST record significantly captures regional SST trends (p<0.05). A 20-year smoothed reconstruction of DJFM SST reveals significant interdecadal co-variability with the NAO since the mid-1800s, with two notable exceptions: (1) around the mid-1920s, and (2) after the mid-1970s. While multiple factors may have contributed to the observed decoupling between the NAO and tropical Atlantic SST, both events were found to have coincided with an eastward displacement and expansion of the Icelandic Low-pressure center of action, leading to a breakdown in the NAO-SST tripole relationship. Our findings suggest that boreal winter tropical North Atlantic SSTs are closely linked to interdecadal NAO variability and are sensitive to the non-stationary behavior of the NAO, which is likely driven by changes in the spatial orientation and configuration of its atmospheric centers. Our work contributes to filling a critical gap in marine-based records of the NAO in the tropical North Atlantic and underscores the importance of understanding long-term decadal-scale climate variability in this region.
How to cite: Ong, M. R., Goodkin, N., Guppy, R., Hu, H.-M., Shen, C.-C., and Hughen, K.: Non-Stationary Interdecadal Variability in the North Atlantic Oscillation Revealed in a 185-Year Coral-Based Sea Surface Temperature Record from the Western Tropical North Atlantic, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4127, https://doi.org/10.5194/egusphere-egu26-4127, 2026.
In this contribution, potential drivers of central European temperature oscillations and trends, related to both external forcings and internal climate variability modes, are explored through statistical analysis of several temperature time series, spanning the period since 1501 CE. The target data include local temperature reconstructions, derived from a combination of instrumental and documentary sources, as well as temperature fields approximated by the ModE-RA paleo-reanalysis. To identify and quantify the contributions attributable to individual climate-influencing factors, linear and nonlinear regression analysis techniques are applied to extract temperature components related to external climate forcings (solar and volcanic activity, radiative balance changes) and to teleconnections projected by large-scale internal climate variability modes (NAO, ENSO, as well as decadal variability originating from the Atlantic and Pacific regions). Attention is also paid to the possible manifestations of nonlinearities in the links between climate drivers and the temperature responses, to the presence of non-stationarities and inhomogeneities in the data, and to the differences in results obtained for different proxy-based reconstructions of the explanatory variables.
How to cite: Mikšovský, J., Holtanová, E., Dobrovolný, P., Brázdil, R., Marčeková, M., Koláček, J., and Skala, P.: Imprints of climate variability drivers in multi-centennial central European temperature series, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4543, https://doi.org/10.5194/egusphere-egu26-4543, 2026.
Analysing longer time periods than what is covered by modern instruments helps to gain further insights into the climate system, its variability and understanding of historical climate events. However, to study the period before the availability of state-of-the-art instrumental measurements, e.g., to analyse the intra-annual dynamics of past climate changes, datasets with a high temporal resolution are required. For this, paleo-reanalyses are an essential solution.
By assimilating observational, documentary and proxy climate information into atmospheric general circulation model simulations, a full 4D field of reality-informed gridded climate information is produced. However, data for assimilation becomes increasingly sparse as we move into the past, particularly during boreal winter seasons and in unpopulated regions.
Here we present a new idea for alleviating this issue: The assimilation of full-field seasonal climate hindcasts for boreal winter months, initiated during high-confidence boreal summer months of the reanalysis. These machine-learning driven hindcasts provide a multi-member output, which helps to map uncertainties accordingly.
In our presentation, we will discuss initial results regarding the skill of these hindcasts and a way forward in assimilating these data for creating a new paleo-reanalysis data set.
How to cite: Franke, J., Wegmann, M., Hilfiker, L., and Brönnimann, S.: The road to assimilating climate hindcasts into paleo-reanalyses, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5969, https://doi.org/10.5194/egusphere-egu26-5969, 2026.
Climate variability exists at all timescales. However, most paleo data assimilation (PDA) reconstructions are validated against relatively short instrumental measurements. This validation process fails to reveal PDA variability information at long timescales. Here, we compare the variability over the Common Era of near surface air temperature, hydroclimate, and sea level pressure of different PDA reconstructions: 1) the Last Millennium Reanalysis (LMR) project, 2) the Paleo Hydrodynamics Data Assimilation product (PHYDA), and 3) a global monthly paleoreanalysis of the modern era (ModE-RA). Although all PDA reconstructions use a similar version of the ensemble Kalman filter, they differ in important methodological choices. We assess differences in loss of variance, reconstruction uncertainty, spectral features, and the power-scaling exponent ß, globally and regionally. For clarity, higher ß-values would indicate a stronger dominance of longer timescales in the power spectrum. We find that ModE-RA has the largest uncertainty levels and the lowest ß-values across all climate indices globally and regionally; it also shows, in most cases, the largest changes in uncertainty and the greatest loss of variability. Furthermore, reconstructions that differ only by prior models show systematically higher or lower ß-values, globally and regionally, across all climate indices. Indeed, when reconstructions differ, they tend to differ systematically, having universally higher or lower ß-values. Differences in spectral power and ß-values between offline and online reconstructions are surprisingly small but vary across regions. Our results show that different, reasonable methodological choices substantially affect the variability of PDA reconstructions.
How to cite: Pliemon, T., Steiger, N., and Hébert, R.: Large spectral differences in paleo data assimilation reconstructions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10072, https://doi.org/10.5194/egusphere-egu26-10072, 2026.
Droughts are associated with widespread adverse impacts across social, economic and ecological systems (Wilhite, 1992; Wilhite et al., 2007). The frequency, severity and persistence of drought events have increased across much of the Earth’s surface over the 20th and 21st centuries, and increasingly droughts coincide with periods of elevated temperature generating compound hot-dry conditions (Dai, 2011; Mazdiyasni and AghaKouchak, 2015; Chiang et al., 2021; King et al., 2024; Gebrechorkos et al., 2025).
However, drought is a complex natural hazard that can result from both natural climate variability and anthropogenic influence (Wilhite and Glantz, 1985; Wilhite, 2000). With less than 100 years of instrumental data across much of the Earth’s surface, and the most severe droughts developing over an extended period, extreme droughts are few (Brunner et al., 2021; Seneviratne et al., 2021; Williams et al., 2022). It is therefore challenging to characterise worst-case outcomes, which is crucial for informing adaptation efforts.
Here we use the Palmer Drought Severity Index (PDSI) calculated from CMIP6 last millennium simulations and independent PDSI reconstructions from tree-ring width chronologies to characterise drought conditions over the last millennium and place recent extreme drought conditions within a longer-term context. The two datasets are used together to establish how the relative severity of extreme drought conditions varies between regions, the frequency with which these events occur, and the extent to which such events are generated by compound hot-dry conditions. Extreme value statistics are then applied to the three PDSI datasets to estimate the severity of 1-in-10, -50, and -100-year summer droughts and assess how these values vary between the datasets. The extremes of the last millennium are then compared to those of the instrumental period. Results highlight regions that are yet to experience droughts during the instrumental period that exceed those of the last millennium; these areas may be particularly vulnerable to future extremes, particularly where these are enhanced by anthropogenic warming.
How to cite: Taylor, K., Hegerl, G., Evans, M., and Schurer, A.: Quantifying Extreme Drought Risk using Palaeoclimate and Model Observations from the Last Millennium , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20440, https://doi.org/10.5194/egusphere-egu26-20440, 2026.
The Ter-Llobregat basin system, located in Catalonia, supplies water to more than 100 municipalities, including Barcelona, serving a population of approximately 5 million. Recently, severe water shortages have prompted emergency measures to restrict consumption. Given the limited and fragmented nature of historical streamflow records, a deeper understanding of past hydrological dynamics is crucial. Tree-ring data has shown considerable potential for reconstructing streamflow series from limited instrumental data.
Here we present a four-century streamflow reconstruction for the upper course of the Llobregat River basin using streamflow data and stable oxygen (δ¹⁸O) and carbon isotope (δ13C) tree-ring chronology from a Pinus uncinata forest growing on the Pedraforca mountain (42°14′23.79″N, 1°42′10.58″E, 2,497 m.a.s.l.) in Catalonia, Spain. For the same period, we also examine historical flood events that occurred across the basin based on typology (fluvial or pluvial), intensity, and seasonality.
Despite the challenges posed by short, discontinuous instrumental records, we obtained robust mean reconstruction statistics with models built using 24 years of non-continuous streamflow data applying a leave-N-out calibration-validation procedure. This demonstrates the potential of the tree-ring isotopic chronologies. Indeed, the δ¹⁸O and δ13C records achieved significant correlation values up to –0.671 and –0.71, respectively, with mid-to-late summer total runoff streamflow records, while the ring-width chronology shows no-clear sensitivity to hydrological variability. The resulting streamflow reconstructions span the period 1600–2002. The δ¹⁸O-based model explains about 25% of the variance in the instrumental period, whereas the δ¹³C-based model explains up to 40%, providing valuable insight into wet and dry periods and extreme years over the past four centuries. Future work including older trees and additional tree-ring sites in the study region could further extend and improve the streamflow reconstruction beyond 400 years.
This four-century streamflow reconstruction provides the first benchmark to characterize natural variability and extremes in the upper Llobregat basin. Placing recent hydrological variability in a centennial-scale long-term perspective is essential for improving water resources management approaches and supporting local-scale risk planning.
How to cite: Lloberas-Millan, G., Tuset, J., Baslasch, C., Barriendos, M., Gutiérrez, E., Molowni-Horas, R., Pino, D., Rodríguez-Morata, C., Del-Stabille, F., Barriendos, J., and Andreu-Hayles, L.: Reconstructing 400 years of streamflow in the upper Llobregat basin (Catalonia, Spain) using stable isotopes in tree rings , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21050, https://doi.org/10.5194/egusphere-egu26-21050, 2026.
Understanding modern warming in a long-term geological context and separating natural forcing from internal variability remain key challenges in paleoclimatology. The Common Era (last two millennia) provides an important bridge between paleoclimate and the instrumental period. Yet building global proxy databases is often limited by manual literature review, data extraction, and metadata curation, which tasks that are time-consuming and can introduce inconsistencies.
We present an LLM-assisted workflow with human oversight to improve proxy database construction. Large Language Models (LLMs) are used to parse peer-reviewed paleoclimate publications and extract metadata such as sampling coordinates, temporal coverage, resolution, archive and proxy types, dating methods, and the authors' climate interpretations. The extracted information is then organized into a consistent format and checked through a multi-level quality control (QC) process.
Using this workflow, we compiled data from major community repositories (PAGES2k, ISO2k, ARC2k, SISALv3, ITRDB, and NTPDC) into a dataset of over 12,000 records. The database covers various archives including tree rings, speleothems, sediments, ice cores, corals, sclerosponges, and documentary sources, with around 70 proxy variables (e.g., δ¹⁸O, δ¹³C, tree-ring width). Quality control includes: (i) chronology classification, (ii) expert review of climate targets, and (iii) standardized formatting for analysis.
Initial results show clear cooling signals following major volcanic eruptions (e.g., mid-6th century, 1257 CE, 1815 CE), and selected proxy networks capture ENSO variability and Northern Hemisphere temperature changes reasonably well. Current work focuses on expanding literature coverage through automated search, improving proxy classification with active learning, and developing machine-learning approaches for spatial reconstructions and model-data comparisons.
How to cite: Shi, F.: An LLM-assisted global proxy database for the Common Era, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21959, https://doi.org/10.5194/egusphere-egu26-21959, 2026.
Posters virtual: Fri, 8 May, 14:00–18:00 | vPoster spot 4
EGU26-4208 | Posters virtual | VPS7
Reconstruction of Japan's Cold-Season Climate in the Past Few Hundred Years Using High-Resolution Multi-ProxyFri, 08 May, 14:15–14:18 (CEST) vPoster spot 4
To understand the climate conditions in Japan before the commencement of modern official meteorological observations, it is necessary to indirectly estimate them using proxy data that serve as climate indicators.
In Japan, there is a nearly continuous annual dataset of Lake Suwa's freezing records spanning over 580 years. Furthermore, diaries from various parts of Japan contain daily weather records. By utilizing these records, daily climate data with the minimum temporal resolution can be obtained. By leveraging these proxies, it is possible to reconstruct the climate of the cold season, which has been previously less understood, across various temporal and spatial scales.
The objective of this study is to reconstruct the changes in cold-season climate in Japan over the past several hundred years with high temporal resolution.
The proxy data currently used include: lake and terrestrial sediments (Lake Suwa, approximately 1000 years), records of cherry blossom flowering and full bloom dates primarily collected in Kyoto (approximately 1000 years), tree rings (approximately 300 years), daily weather records from diaries (approximately 200 years), freezing records of Lake Suwa and Lake Jusan (approximately 580 and 150 years, respectively), early-meteorological observation data (approximately 50 years), and Japan Meteorological Agency observation data (approximately 150 years).
Firstly, the most extensive dataset, the cherry blossom flowering data, is used as a reference. Next, proxy variables are standardized after removing trends caused by human activities. Subsequently, regression analysis is performed for each period where variations either coincide or do not coincide. Furthermore, for each proxy variable, spatial correlations were calculated using 20th-century meteorological observation data to identify the regions represented by that proxy variable.
(This research was funded by JSPS Grant-in-Aid for Scientific Research (24H00118).
How to cite: Hasegawa, N., Katata, G., Hirano, J., Yonenobu, H., Yasue, K., Kumon, F., Hatano, N., Takahashi, H., Zaiki, M., and Mikami, T.: Reconstruction of Japan's Cold-Season Climate in the Past Few Hundred Years Using High-Resolution Multi-Proxy, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4208, https://doi.org/10.5194/egusphere-egu26-4208, 2026.
