The Arctic is experiencing rapid warming, with temperatures rising at 2–3 times the global average. Svalbard, located halfway between Norway and the North Pole, exemplifies this rapid change, experiencing a concerning temperature increase of approximately 4 °C over the past century, and more than double the Arctic average since 1991. This warming is attributed to the influx of warm Atlantic water and air, coupled with a strong poleward flow of moisture in the form of atmospheric rivers. Svalbard's unique location and exposure to oceanic and atmospheric variability make it an ideal location to study long-term hydroclimate changes. Recent observations indicate that rapid hydroclimatic changes are underway, evidenced by exceptionally warm, ice-free seas and above-normal precipitation during the 2015–16 winter. These conditions led to catastrophic mudflows and avalanches in Longyearbyen, highlighting the need to understand the drivers of these extreme events and predict future risks. While thermodynamics can explain long-term Arctic-wide projections, understanding the dynamics and short-term climate variability, particularly the role of atmospheric blocking, is crucial for assessing regional hydrological extremes. Atmospheric blocking plays a vital role in regulating moisture transport in the northernmost reaches of the North Atlantic Current, including three dominant patterns: Scandinavian, Ural, and Greenland blocking. These patterns, especially Scandinavian and Ural blocking, often lead to the advection of warm mid-latitude air masses into Svalbard. However, the impact of climate warming on the characteristics and frequency of these blocking events is still unclear due to limitations in data length and proxy availability. This study uses a multi-proxy approach, combining instrumental data, paleoproxies (lacustrine sediments and tree rings), and paleoclimate model simulations to investigate the long-term perspective on hydroclimate changes and their drivers in Svalbard.

Previous research has highlighted the significant impact of Arctic warming on mid-latitude weather patterns and the role of atmospheric blocking in regulating Arctic warming and sea ice decline. Studies have linked specific blocking patterns, such as Scandinavian, Ural, and Greenland blocking, to various changes in Arctic climate, including sea ice loss and surface melting over the Greenland Ice Sheet. The insufficient length of instrumental data and the lack of suitable proxies to characterize blocking events before the instrumental era have hampered a comprehensive understanding of these phenomena. Existing climate models also vary in their representation of atmospheric blocking, leading to uncertainties in future projections. This study builds upon existing research by employing a novel multi-proxy approach to investigate the long-term interplay between atmospheric blocking, regional climate variability, and Svalbard's hydroclimate.

This study employed a multi-faceted approach, integrating instrumental data, paleoproxies, and climate model simulations to analyze hydroclimate changes in Svalbard and the neighboring Arctic region. Instrumental data (1955-2019), including precipitation from University of Delaware (UDEL) and Global Precipitation Climatology Centre (GPCC) gridded products, atmospheric fields (geopotential height, winds, surface air temperature) from ERA5 reanalysis, and sea surface temperatures (SST) from HadISST+ and ERSST were used to examine the synoptic conditions responsible for recent extreme events and to establish relationships between Svalbard precipitation and atmospheric circulation features. Regression analysis was employed to quantify these relationships. Paleoclimate data utilized an annually laminated sediment record from Lake Linné (Linnévatnet) in western Svalbard. This sediment record, analyzed for grain size and calcium (Ca) content using laser diffraction and Itrax X-ray fluorescence, served as a proxy for past precipitation and temperature variability, especially for heavy rainfall events. The study also incorporated existing tree-ring-based summer temperature reconstructions from Scandinavia and other Eurasian regions to provide a longer-term perspective on temperature and blocking patterns. Climate model data included the MPI-ESM1-2-LR past2k transient simulation (1-1850 CE) to analyze regional circulation and its relation to Svalbard temperature and precipitation, and two CMIP6 models (IPSL-CM6A-LR and MPI-ESM1-2-HR) to project future changes in Svalbard's temperature and precipitation under different emissions scenarios. The Scandinavian Blocking (SB) index was calculated using principal component analysis on 500 hPa geopotential height anomalies to assess its temporal variation and correlation with other climate variables. Sediment traps at Linnévatnet provided high-resolution data on daily sediment fluxes and grain size, allowing for the direct linking of specific precipitation events with the SB index. The analysis covered a broad temporal scale from daily data (sediment traps) to multi-centennial scales (lake sediment cores and tree rings) encompassing the last two millennia.

The study revealed a strong and consistent association between extreme precipitation events in Svalbard and the Scandinavian Blocking (SB) pattern. Analysis of recent extreme events (e.g., 2016) showed that wet conditions in Svalbard are associated with positive mid-tropospheric geopotential height anomalies south and southeast of the archipelago and warmer-than-normal conditions across the region. The SB pattern, characterized by a high-pressure system over northern Scandinavia, diverts the polar jet stream, creating conditions favorable for moisture advection towards Svalbard. Lake sediment analysis from Linnévatnet demonstrated that the coarsest grain-size deposition and high calcium (Ca) values in the lake consistently coincided with periods of heavy precipitation and SB. This relationship is observed both in monthly and daily data. The annually laminated sediment record from Linnévatnet provided a unique long-term perspective on this link, spanning two millennia. The Ca concentration in the sediments, acting as a proxy for rainfall intensity, revealed a long-term decreasing trend from the Medieval period to the Little Ice Age (LIA), with the lowest values between the 1600s and the mid-1800s. This trend reversed around the 1850s, with a steady rise in Ca values, culminating in exceptionally high values during the recent extreme events of 2016. The study found significant co-variability between the Scandinavian summer temperature reconstruction from tree rings and Linnévatnet Ca values, reinforcing the connection between atmospheric blocking, temperature, and precipitation in Svalbard. The study's climate model simulations confirmed the observed relationship between SB and Svalbard precipitation. These simulations also projected a continued increase in mean June-November temperature and precipitation in Svalbard under future warming scenarios, accompanied by a higher frequency of extreme rainfall events.

The findings of this study demonstrate a robust link between atmospheric blocking patterns, particularly the Scandinavian Blocking pattern, and extreme precipitation events in Svalbard over the past two millennia. The annually resolved sediment record from Linnévatnet provides strong evidence for the long-term persistence of this relationship, highlighting the importance of atmospheric dynamics in shaping the region's hydroclimate. The observed correlation between Scandinavian summer temperatures (from tree rings) and Svalbard precipitation further supports the influence of atmospheric blocking on both temperature and precipitation. The study's projections for future precipitation in Svalbard underscore the significant implications of climate change and sea ice decline, suggesting an intensification of extreme rainfall events under continued warming. This has significant implications for infrastructure, human settlements, and ecosystems in the region. While the study focuses on the Scandinavian Blocking pattern, it also acknowledges the influence of other blocking patterns, such as Ural blocking, and the complex interplay between atmospheric circulation, sea ice extent, and regional SST variations.

This study provides compelling evidence of a long-term link between atmospheric blocking events and extreme precipitation in Svalbard. The use of multiple data sources, from high-resolution sediment trap data to multi-centennial proxy records and climate models, strengthens the findings and highlights the importance of atmospheric dynamics in driving hydroclimatic variability in the Arctic. The projected intensification of extreme rainfall events under future climate scenarios emphasizes the need for comprehensive adaptation strategies in Svalbard. Future research could further investigate the role of other atmospheric blocking patterns and refine the projections of extreme precipitation events by utilizing higher-resolution climate models and incorporating more detailed regional climate dynamics.

The study acknowledges limitations inherent in using proxies for climate variables. Although the Ca concentration in Linnévatnet sediments effectively reflects rainfall intensity, it might not perfectly capture the full complexity of precipitation patterns. The tree-ring-based temperature reconstructions are primarily summer proxies, potentially missing nuances in seasonal precipitation variations. Moreover, while the study utilized multiple climate models, uncertainties remain in the representation of atmospheric blocking in climate models, potentially affecting the robustness of future precipitation projections. Additional research using higher-resolution models and longer-term proxy data could address these limitations.