Arctic winter heatwaves: an ever-increasing phenomenon challenging the arctic environment and local communities Workshop

Activity Report

Rising temperatures are increasing the frequency of extreme events, such as summer and winter heatwaves. Such heatwaves, characterized by persistent warm and humid air masses known also as "warm spells", bring prolonged periods of unusually high temperatures and often result in "rain-on-snow" events (ROS). This phenomenon represents an emerging challenge to the Arctic ecosystem and its inhabitants, affecting environmental, ecological, and socioeconomic aspects. Despite their sporadic nature, winter heatwaves impact both coastal and inland areas of the Arctic region. Studying the effects of these extreme events throughout the snow accumulation and melting periods is crucial for understanding their impact on the winter Arctic environment. When rain falls on snow, it creates hard crusts or percolates through the snowpack, forming pools at the snow-ground interface. These processes alter the snow-albedo feedback and accelerate the hydrological cycle associated with snow melting. Therefore, winter heatwaves and ROS events disrupt the snow season by impacting snow accumulation, moistening, and ripening processes, and triggering water runoff through the snowpack. Ultimately, this water presence leads to state transformations and heat transfer processes at the snow-ground interface, resulting in soil warming and permafrost thawing.

A workshop was organized to develop a multidisciplinary strategy to enhance and promote the study of winter warm spells and present these findings to the ICARP IV process. Although warm-spell and heat waves occur in also during summer, the increase frequency and the impact of the winter events are more severe since they are able to directly impact and change the cryosphere and all the environmental process (biological and no) link to it. The objective was to create a roadmap for investigating the impact of winter warm spells on the Arctic environment and to highlight their potential socioeconomic effects on local communities and activities in the Arctic region. The event, organized by the Institute of Polar Science (ISP-CNR, Dr. Andrea Spolaor) in collaboration with the Institute of Atmospheric Pollution Research (IIA-CNR, Dr. Roberto Salzano), took place from June 11st to 13th, 2024 at Montegrotto, Italy. It brought together experts and researchers from various European and non-European institutes specializing in the polar environment. Topics covered by the invited participants included the impact of Arctic winter warm spells on snow chemistry and aerosol composition, including anthropogenic contaminants (Spolaor, Cairns, Wang, Barbaro, Ardini); snow physics (Van Pelt, Luks, Salzano, Valt, Scoto); snow albedo (Pirazzini, Salzano, Cappelletti); composition and microbial activity in the snow (Larose, Keuschnig); remote sensing of the snow cover (Salzano); and the role of snowmelt in surface and subsurface hydrology (Diogo Costa, Moser, Guyennon). The scientific meeting aimed at deepening discussions about the consequences and activities necessary for understanding the impact of winter warm spells on the Arctic environment and related socioeconomic aspects.

The workshop was divided into three days. On the first day, the invited participants arrived, and the objectives and goals of the workshop were outlined, link to the ICARP IV process. On the second day, each participant was asked to present their research activities, specifically focusing on how Arctic heat events might impact their specific scientific field, identifying unanswered questions, and discussing the requirements for improving their studies, as well as possible connections or synergies with other scientific disciplines. Each presentation lasted approximately 15 minutes, followed by time for questions, comments, and additional information from other participants. On the third day, the group worked on drafting a common document outlining the research priorities related to these events and the associated needs. Three main research priorities emerged from the workshop, each accompanied by the necessary actions to address them, which will be presented to IASC and the ICARP IV process.

Three highlights:

• Increased frequency of extreme warm events during winter in certain Arctic regions, driving significant environmental changes in the cryosphere.
• Direct impacts on the coastal snowpack, hydrological systems, ecosystems, and local wildlife, altering natural processes and habitats.
• Specific metrics are necessary for accurately identifying and characterizing these extreme events to enhance predictive models and to support decision-makers.

Summary of input provided for the ICARP IV process

The input highlights the need for collaborative, multidisciplinary research efforts to address the increasing threat of Arctic extreme events, such as winter heatwaves and rain-on-snow occurrence. The identification of those extreme events is at the moment based on single-domain requirements (meteorological, marine, ecological, human health) and on mid-latitude conditions. More effort must be addressed to adapt criterias to the Arctic environment, assessing the impacts on the atmosphere-cryosphere interface, and potential feedbacks on the connected ecosystems and human activities.The priorities focus on enhancing data collection, improving climate models, understanding ecological and societal impacts, and working with Indigenous communities to develop effective adaptation strategies. These priorities align with key ICARP IV topics, including climate dynamics, vulnerability and resilience, and Indigenous knowledge co-production. Here the research priorities and needs.

• Research Priority 1: Will Arctic Winter Warm Spell Events in the Arctic Become More Widespread, Frequent and Intense in a Changing Climate?
• Research Priority 2: Process-Based Understanding of Arctic Winter Warm Spells on the Arctic Environment at Event and Seasonal Timescales.
• Research Priority 3: Knowledge Co-Creation of Current and Future Downstream Consequences on Ecosystems and Society together with Arctic Communities.

Recommendations for priorities in Arctic research for the coming decade

Below is the list of recommendations and needs linked to each of the research priorities mentioned in the previous point and produced during the workshop.

Research priority 1:

1. Develop a shared definition of Arctic Winter Warm Spells (AWaS): Establish a standardized definition that is relevant across the entire Arctic region that is applicable to the whole ecosystem. Standardize several existing definitions (focused mainly on human health, marine environments and ecosystems located at mid-latitudes), with a set of indicators aimed at assessing the impact of extreme events on the cryosphere. This definition will facilitate consistency, clarity, and communication across various disciplines and regions.
2. Access to long-term, intercomparable, and harmonized datasets and observations: Increase both in-situ and remote data to study the frequency, duration, and intensity of AWaS from a pan-Arctic perspective. These datasets should include Essential Climate Variables (ECV) to ensure comprehensive monitoring and analysis. Consistent and high-quality data are crucial for understanding long-term trends and variations.
3. Improve model performance: Enhance climate and numerical weather prediction model to better simulate AWaS at the finest possible scale, ensuring they can accurately represent spatial variability. This improvement is essential for making reliable climate projections and understanding future scenarios. High-resolution models will help predict localized impacts and aid in developing targeted adaptation strategies.

Research priority 2

1. Source and composition of air masses: Investigate the origins and characteristics of air masses that lead to winter warm spells. Understanding the pathways and properties of these air masses will reduce uncertainties in predicting future events and their impacts.
2. Precipitation phase change: Study how winter warm spells affect the phase change of precipitation (from snow to rain or mixed precipitation). This has significant implications for the hydrological cycle, snowpack dynamics, and overall Arctic climate system.
3. Improve snowpack representation in Earth system models: Enhance the representation of multi-layered snowpacks in Earth system models, using new and existing observational data. Accurate snowpack modelling is crucial for predicting melt, refreezing and runoff water contributions and changes in albedo.
4. Impact on the cryosphere: Examine the effects of winter warm spells on the physical and optical properties, chemistry, and biology of the cryosphere. This includes studying changes in sea and lake ice, snowpack, permafrost, and glacier dynamics. Understanding these impacts is vital for assessing the broader implications for the Arctic environment.
5. Impact on hydrology: Analyze how winter warm spells influence hydrological processes, such as flooding and ice jams. Changes in river and stream flows can have downstream effects on ecosystems and human communities.
6. Nutrient and contaminants (re-)mobilization and microbial signatures: Investigate how winter warm spells affect the biogeochemical cycles, including the mobilization of nutrients and pollutants, the translocation of microbes as well as their altered activity and function. These processes are important for preserving impurity records that are useful climate and environmental proxies and understanding ecological impacts.
7. Increased occurrence of avalanches: Assess how winter warm spells contribute to the frequency and intensity of avalanches and landslide. This is crucial for hazard prediction and mitigation, especially for communities and infrastructure in avalanche-prone areas

Research priority 3

1. Current and future effects on terrestrial ecosystems: Study the impacts of winter warm spells on terrestrial ecosystems, such as the formation of ice layers that affect reindeer herding, burrowing animals, and downstream habitats, as well as vegetation changes. These effects can have profound implications for biodiversity and the livelihoods of Indigenous communities.
2. Current and future effects on marine ecosystems: Examine the consequences of winter warm spells on marine ecosystems, including sea ice, coastal and fjord regional ecology, coastal erosion, and freshwater-marine coupling. Understanding these impacts is essential for managing marine resources and protecting coastal habitats.
3. Related hazards for local populations: Identify the hazards posed by winter warm spells to human populations, such as challenges to winter mobility, tourism, water and food safety, security, and energy production. Addressing these hazards requires comprehensive risk assessments and the development of mitigation strategies.
4. Developing adaptation strategies: Create and implement adaptation strategies to help Arctic communities and ecosystems become more resilient in the face of changing climate conditions. These strategies should be co-developed with Indigenous communities to ensure they are culturally appropriate and effective.
5. Knowledge Co-production with Indigenous communities: This will involve incorporating their traditional knowledge and perspectives to enhance the relevance, applicability, and accessibility of research outcomes. Collaborative approaches will foster resilience and sustainability in the Arctic region

Recommendations for the implementation of the suggested priorities

The recommendation for the implementation of the research priorities by defined needs are provided in the previous point. The full documents is uploaded as separate file summarize all the point and outcome discussed during the workshop. The topic of the Arctic heat waves can be associated to several scientific aspect and research fields. Below are listed and described the link of research priorities identify during the workshop with the ICARP IV topics area.

RESEARCH PRIORITY 1

Link to ICARP IV Topic Area 2: Observing, Reconstructing, and Predicting Future Climate Dynamics and Ecosystem Responses
Observing and Predicting Climate Dynamics: The need for standardized definitions, harmonized datasets, and improved climate models directly supports efforts to observe and predict future climate dynamics, including the occurrence and intensity of winter warm spells. Extreme events are now defined for specific domains such as Health, Marine and Ecosystems. A cryosphere-oriented definition is highly recommended to emphasize how cryospheric components are impacted by extreme events, as the cryosphere interacts with numerous other spheres and, in turn, influences various other environmental systems.

RESEARCH PRIORITY 2

Link to ICARP IV Topic Area 2: Topic Area 2: Observing, Reconstructing, and Predicting Future Climate Dynamics and Ecosystem Responses
Process-based Understanding: Studying air mass sources, precipitation phase changes, snowpack dynamics, and impacts on the cryosphere contribute to understanding how these processes influence Arctic climate dynamics and ecosystem responses.
Link to ICARP IV Topic Area 7: Technology, Infrastructure, Logistics, and Services
Infrastructure and Services: Addressing the technological and logistical challenges of monitoring and predicting winter warm spells and their impacts supports advancements in technology, infrastructure, logistics, and services necessary for effective Arctic research and adaptation efforts.

RESEARCH PRIORITY 3

Link to ICARP IV Topic Area 3: Understanding the Vulnerability and Resilience of Arctic Environments and Societies and Supporting Sustainable Development
Understanding Vulnerability and Resilience: Assessing the impacts on terrestrial and marine ecosystems, hazards to human populations, and developing adaptation strategies aligns with understanding the vulnerability and resilience of Arctic environments and societies. Knowledge co-production with Indigenous communities ensures the relevance and effectiveness of adaptation strategies.

Link to ICARP IV Topic Area 5: Co-Production and Indigenous-led methodologies
Co-Production and Indigenous Knowledge: The recognition of the necessity to co-develop with Indigenous communities for research and adaptation strategies directly supports Topic Area 5, which focuses on co-producing knowledge and including Indigenous-led methodologies.

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