2.9. Meteorology, Environmental and Livelihood Impacts of Arctic Rain-on-Snow Events

27 March 2025 | 10:30 - 12:00 (MDT)

Open Session - HYBRID

Room:  UMC Fourth Floor - 415 / 417

Organisers:  Mark Serreze (National Snow and Ice Data Center, University of Colorado Boulder, USA); Andrew Barrett (National Snow and Ice Data Center, University of Colorado Boulder, USA); Alex Crawford (University of Manitoba, Canada)

Session Description:

When rain falls on an existing cover of snow, followed by low temperatures, or falls as freezing rain, it can leave a hard crust. These Arctic rain-on-snow (ROS) events can profoundly influence the environment and in turn, human livelihoods. Impacts can be immediate (e.g. on human travel, herding, or harvesting) or evolve or accumulate, leading to massive starvation-induced die-offs of reindeer, caribou, and musk oxen, for example. Much remains to be learned about the meteorological conditions leading to ROS events and subsequent freezing, including links with the atmospheric circulation at the scale of planetary waves to the mesoscale to the local scale, their frequent association with atmospheric rivers, the distribution of events across the Arctic landscape and ocean, and whether events are becoming more common or severe in the warming climate. In turn, obtaining knowledge and information most germane to impacts, such as the thickness of ice layers, how ice layers form within a snowpack, and antecedent conditions that can amplify impacts, necessitates collaboration and knowledge co-production with community members and Indigenous knowledge-holders. This session invites contributions on all aspects of rain-on-snow events, and especially those that bridge different types of observations and ways of knowing to understand environmental and livelihood impacts.

Instructions for Speakers:  Oral presentations in this session should be at most 8-minutes in length, with an additional 2 minutes for questions (unless more detailed instructions are provided by session conveners). See more detailed presenter instructions here.

Oral Presentations: 

• unfold_moreAnalysis of the Rain-on-Snow Event in December 2021 in Interior Alaska Using the Arctic Regional Reanalysis (ARR) and ERA5 — Kazuyoshi Suzuki 

  Kazuyoshi Suzuki ¹; Milija Zupanski ²; Akira Yanmazaki ¹; Takashi Dan ¹; Hotaek Park ¹; Tetsuya Hiyama ³; Go Iwahana ⁴; Hideki Kobayashi ^{1
  1} Japan Agency for Marine-Earth Science and Technology; ² Colorado State University; ³ ISEE, Nagoya University; ⁴ IARC, University of Alaska Fairbanks

  Format: Oral in-person

  Abstract:

  A record-breaking precipitation event was observed in interior Alaska on 26 December 2021, with daily maximum precipitation of nearly 100 mm in both Fairbanks and Poker Flat, located farther north in the near Arctic Circle. Monthly precipitation in December exceeded 200 mm at both locations, with Poker Flat recording the higher precipitation. In this study, we clarify the contribution of a significant rain-on-snow event to the precipitation that exceeded typical summer levels in the Arctic, using in-situ observations and reanalysis datasets. Additionally, the effects of the record-breaking precipitation on the snowpack, soil layer, and the water and energy balance were analyzed. Simultaneously, we are developing an Arctic region system reanalysis (ARR) using Polar WRF-MLEF. We attempted to reproduce the anomalous precipitation from the reanalysis values using our system. Furthermore, we assessed the impact of AMSR2’s sea surface wind retrieval and tower meteorological observations. Analysis using ERA5 and ARR suggested that the extreme precipitation was caused primarily by a low-pressure system developing over the Kamchatka Peninsula, an Aleutian low extending from Kamchatka, and a blocking high-pressure system over the Northeast Pacific Ocean south of Alaska. Additionally, a high sea surface temperature anomaly contributed to the increased atmospheric moisture during the event.

• unfold_moreCritical Seasonal Conditions in the Reindeer-Herding Year: A Synopsis of Factors and Events in Fennoscandia and Northwestern Russia — Bruce C. Forbes 

  Bruce C. Forbes ¹; Roza Laptander ^{2
  1} Arctic Centre, University of Lapland; ² Universitåt Hamburg, Institut für Ethnologie

  Format: Oral in-person

  Abstract:

  We identify what herders in Fennoscandia and northwestern Russia see as critical conditions and events in the annual reindeer herding cycle. Indigenous S´ ami and Yamal reindeer herders identify eight seasons, each of which has crucial importance in its own way. Differences in perception between Fennoscandian and northwestern Russian reindeer herders about good and bad seasonal conditions are based on the degree of climatic and geographic variation, herd control and the variety of simultaneous pressures on pastures. The scope and speed of ongoing climate change in the Arctic will profoundly modify these conditions, and consequently shape critical events and outcomes in reindeer herding. The resulting challenges need to be assessed in the context of social and economic dynamics. Reindeer herders throughout Fennoscandia and Russia are concerned about future prospects of their livelihood. To adapt to climate change and develop new strategies, reindeer herders must have access to pastures; they must retain their mobility and flexibility; and their participation in land-use decisions must be endorsed.

• unfold_moreA comprehensive snow monitoring system to detect the impact of rain-on-snow (ROS) events on the seasonal snowpack and hydrological system on Svalbard — Federico Scoto 

  Federico Scoto ¹; Roberto Salzano ²; Antonio Donateo ³; Giuanluca Pappaccogli ⁴; Mauro Mazzola ⁵; Andrea Spolaor ^{6
  1} Institute of Polar Sciences, National Research Council (ISP-CNR); ² Instutute of Atmospheric Pollution Research, National Research Council (IIA-CNR); ³ Institute of Atmospheric Sciences and Climate, National Research Council (ISAC-CNR); ⁴ University of Salento; ⁵ Institute of Polar Sciences, National Research Council (ISP-CNR); ⁶ Instutute of Polar Sciences, National Research Council (ISP-CNR)

  Format: Oral in-person

  Abstract:

  Driven by Arctic amplification, the Svalbard Archipelago has experienced warming at a rate four times higher than the global average over the last decades. This has led to more frequent warm spells and associated rain-on-snow (ROS) events, particularly in winter. ROS events have a significant effect on snowpack properties, glacier mass balance, local ecosystems, and infrastructures. Given the expected increase in frequency and intensity of these phenomena in the coming years, it is essential to improve our understanding of such extreme weather events and particularly of their effects on the seasonal snow cover.

  The assessment of the spatial distribution impacts on the cryosphere is commonly approached by numerical modelling and remotely sensed observations (spaceborn or airborn), but a multi-scale gap occurs without specific ground-based measurements.

  To bridge this gap, and closely examine the impact of ROS on the snow cover, a comprehensive snow observing system was installed in late 2020 in Ny-Ålesund (West Svalbard). It provides high-resolution measurements of snow depth, SWE, albedo, snow temperatures, and LWC profiles. Over the first three years, the nivometric station has significantly enhanced our understanding of the physical/chemical modifications occurring in the snowpack in response to extreme events. The results showed rapid increases in snow temperature and wetness during warm spells, providing new insights into the snowpack dynamics that are essential for determining the thresholds that could activate hydrological systems. Here we present the observational set-up, the data collected, and potential strategies for local communities to prevent the consequences related to ROS events.

• unfold_moreHow do atmospheric rivers get into the Arctic? — Hua Lu 

  Luisa Aviles Podgurskia ¹; Patrick Martineau ²; Ayako Yamamoto ³; Hua Lu ¹; Thomas Bracegirdle ¹; Tony Phillips ^{1
  1} British Antarctic Survey, UK; ² Japan Agency for Marine-Earth Science and Technology; ³ J. F. Oberlin University

  Format: Oral in-person

  Abstract:

  More than 90% of the precipitable water in the Arctic is transported via atmospheric rivers (ARs)—long, narrow corridors of concentrated water vapor in the atmosphere. These ARs play a crucial role in the Arctic climate system, significantly influencing extreme weather events such as rain-on-snow occurrences, which have substantial socioeconomic implications.

  In this study, we present detailed case studies of three AR events observed during the MOSAiC expedition (2019-2020). By employing backward air parcel tracking techniques, we trace the pathways of moisture uptake and transport into the Arctic associated with these ARs. Furthermore, we analyze the synoptic weather patterns, including cyclones, blocking systems, and other large-scale atmospheric features, including the low-level jet that influenced the trajectories and steering of these moisture-laden air parcels.

  This research provides a process-based understanding of Arctic ARs by uncovering the dynamical drivers and evaluating the relative contributions of various physical processes along the AR paths. Our findings shed light on the mechanisms driving AR-related precipitation in the Arctic and their potential impacts on regional weather and climate, offering valuable insights into the complex interactions within the Arctic climate system.

• unfold_moreEvaluating potential change in future rain-in-winter hazards and potential travel risks in three subarctic communities — Jennifer Schmidt 

  Peter Bieniek ¹; Jennifer Schmidt ²; Matthew Berman ²; Rick Thoman ^{1
  1} University of Alaska Fairbanks; ² University of Alaska Anchorage

  Format: Oral in-person

  Abstract:

  Rainfall during the winter months in Arctic and high-latitude communities freezes on infrastructure and often does not fully melt until the spring thaw. Such rain-in-winter (RIW) events pose hazards for communities. Given the potentially increasing hazard, communities need to prepare to mitigate the risks. This study aimed to identify historical and projected changes in RIW for three communities in Alaska and Canada - Anchorage, Fairbanks, and Whitehorse - to support local scenario planning efforts. Observational data from Anchorage and Fairbanks identified increasing frequencies of RIW since the 1960s. Initial community meetings in Whitehorse identified mid-winter temperature fluctuations resulting in thawing-freezing as a primary hazard that observations also identified as occurring more frequently over the period of record. Future projections from four global climate models showed RIW increasing in frequency into the future for all three communities, with a shortened season in Anchorage. Anchorage was further complicated by its steep topography and spatial precipitation gradient within the city. Dynamically downscaled reanalysis and local weather station observations reveal that this complex local climatology generates enhanced RIW at higher elevation and southeastern areas of the city. Specialized statistical analysis of common travel routes identified surface transportation issues unique to the community, including higher risks for travel for residents of these enhanced hazard neighborhoods. The results of this study point to increased future RIW hazards already ongoing in Fairbanks and Anchorage and potentially emerging as an issue for Whitehorse.

• unfold_moreEvaluating Rain on Snow Events on the summit of Mount Washington, New Hampshire and The Possible Future Impacts of a Changing Climate — Charlie Peachy 

  Hayden Pearson ^1,2; Charlie Peachy ^{1
  1} Mount Washington Observatory; ² University of Tromsø

  Format: Oral in-person

  Abstract:

  This study investigates the characteristics of rain-on-snow (ROS) events on the summit of Mount Washington, New Hampshire, using data from the daily weather observations taken at the Mount Washington Observatory from 1981 to 2020 to create two different climatologies (1981-2010 and 1991-2020). Several metrics were used to evaluate ROS events, including the frequency and duration of ROS events, the total amount of precipitation during the events, and their impact on snowpack stability and the surrounding watershed. Based on these metrics, several statistically significant (p < 0.05) trends were found in the data set, and a case study was then performed to investigate the characteristics of a ROS event that occurred on December 18-19, 2023, which resulted in record flooding across the majority of Northern New England. Notably, a positive increase in ROS events was found for both climatologies, but the highest increase happened in the most recent two climatologies. Furthermore, the decadal trends showed that the most recent decade (2011-2020) shifted the maximum number of ROS events from November to December relative to the other three decades (1981-2010), indicating a shortening winter season and weakening snowpack. Additionally, the December 2023 event case study showed how the snowpack characteristics at the beginning of the winter season can significantly contribute to the flooding associated with ROS events, particularly one that produced an 800-year flood.

• unfold_moreA Comprehensive Analysis of Trends and Changes in Precipitation Partitioning over the Arctic Ocean — Zaria Cast 

  Zaria Cast ^{1
  1} University of Colorado at Boulder

  Format: Oral in-person

  Abstract:

  As the Arctic warms, rain-on-snow (ROS) events are likely to become more common and increase in severity. While past research has highlighted the impacts of ROS events over land, such as impacts on reindeer herding, the frequency, characteristics and impacts of ROS events over the Arctic Ocean are not well known. This study evaluates ROS events from 1979 to present using ERA-5 reanalysis data over both land and sea-ice in the Arctic. This analysis focuses on the spatial and seasonal distribution of ROS events, specifically the frequency, intensity and meteorological conditions associated with them. We assess monthly trends in ROS events from 1979 to present-day. Lastly, we analyze the impact of ROS events on Arctic sea-ice persistence and stability by evaluating links between ROS and sea-ice age. Overall, the findings will provide more knowledge on the changing climate in the Arctic, highlighting implications for the future of Arctic Sea ice and offering insights for improved model predictions.

• unfold_moreArctic-wide comparison of ROS events from station data and reanalysis — Michelle McCrystall 

  Michelle McCrystall ¹; Julienne Stroeve ²; Skylar Park ³; Andrew Barrett ^{4
  1} University of Auckland; ² University of Manitoba, University College London; ³ University College London; ⁴ National Snow and Ice Data Centre, Boulder Colorado

  Format: Oral virtual

  Abstract:

  Increases in rainfall has been observed across the Arctic in all seasons. The occurrence of liquid precipitation in winter, however, when there is snow-cover on the ground, can result in rain-on-snow events. These events can have significant impacts such as increasing snow melt and subsequent flooding, or, if followed by freezing temperatures, generate ice layers within the snowpack. These ice layers inhibit winter foraging for reindeer and caribou and in extreme conditions lead to starving and die off events. Current analysis of ROS events is limited to country-specific or single reanalysis-focused studies with limited input from station observations. Therefore, an accurate understanding of ROS across the Arctic and its subsequent impacts is lacking.

  This study addresses this gap through the generation of a pan-Arctic ROS database from station observations from 1979 through to 2022. We compare this data to a pan-Arctic ROS database generated from ERA5 reanalysis for an extended winter period from October-March. The comparisons between these two datasets shows that ERA5 largely underestimates the number of ROS events relative to the station data. Assessing rainfall amounts between the two datasets shows that ERA5 has too low rainfall with monthly average rainfall at 60mm compared to station data which is approximately 180mm. These results follow previous studies that shows that ERA5 has too much drizzle and not enough rain events at higher quantities therefore impacting the assesment of rainfall, including ROS events, across the Arctic from reanalysis data.

 

Poster Presentations (during Poster Exhibit and Session on Wednesday 26 March): 

• unfold_moreLinking Arctic Rain on Snow Events with Atmospheric Rivers — Mark Serreze 

  Mark Serreze ¹; Jessica Voveris ^{2
  1} University of Colorado Boulder; ² Aur Force Weather

  Format: Poster in-person

  Poster number: #263

  Abstract:

  Arctic rain-on-snow (ROS) events can have significant impacts on Arctic wildlife and socioeconomic systems. This study addresses the meteorology of Arctic ROS events from two case studies, with comparisons with other known significant cases. The first event, occurring near Nuuk, Greenland, generated significant impacts, including slush avalanches. The second, less severe, event occurred within the community of Iqaluit, Nunavut. Atmospheric blocking played a leading role in ROS initiation for these and other events, with atmospheric rivers – narrow bands of high water vapor transport, typically originating from the tropics and subtropics – having both direct and indirect effects. Cyclone induced low-level jets and resultant ‘warm noses’ of higher air temperatures and moisture transport are other key features in ROS generation. To our knowledge, our study is the first to visualize how the varying strength and manifestation of these coupled features contribute to differences in the severity of Arctic ROS events. The meteorological drivers identified here find support from other studies on Arctic ROS events and are similar to weather features associated with Arctic precipitation events of extreme magnitude.

• unfold_moreNegative impact of the snow to rain transition of extreme summer precipitation events on the Greenland Ice Sheet surface mass balance — Alex Crawford 

  Nicole Loeb ¹; Alex Crawford ²; Julienne Stroeve ^{3
  1} Department of Environment and Geography, Univeristy of Manitoba; ² Department of Environment and Geography, University of Manitoba; ³ Centre for Earth Observation Science, University of Manitoba, National Snow and Ice Data Center, University of Colorado, Alfred Wegener Institute

  Format: Poster in-person

  Poster number: #306

  Abstract:

  Mass loss from the Greenland Ice Sheet is projected to contribute several centimeters of sea-level rise by 2100. Historically, extreme precipitation events over the Greenland Ice Sheet have been predominantly positive contributors to its surface mass balance (SMB), either adding snow or adding rain that percolates through the surface snowpack and firn layers before freezing into ice lenses. In other words, even when rain-on-snow is occurring, historical extreme precipitation events have typically led to mass gains for the Greenland Ice Sheet. Using simulations from the Regional Atmospheric Climate Model (RACMO) and a variable resolution configuration of the Community Earth System Model (VR-CESM), we show that, in a strong warming scenario (SSP5-8.5), the SMB of the Greenland Ice Sheet switches from consistently positive during summer extreme precipitation events historically to commonly negative by 2100. In southwest Greenland, the switch is more dramatic, with the SMB during extreme summer precipitation switching from always positive historically to always negative by 2100. Across Greenland, the SMB response to extreme precipitation events also becomes more variable, with the interquartile range increasing by 20% to 200% from historical by 2100. This transition coincides with a shift toward a greater fraction of extreme precipitation falling as rain, an increase in the total precipitation occurring during extremes, and an increase in runoff (and therefore mass loss) during extreme precipitation events. In short, the shift to more rain means that extreme precipitation events will no longer reliably counteract summer surface mass loss for the Greenland Ice Sheet.