Enhancement of Local Hydrometeorology and Impacts on Tundra Wildfire and Subsistence Food Security on the Yukon-Kuskokwim Delta

Changing precipitation in the Arctic is an important indicator of Arctic climate change, which is occurring at accelerated rates due to Arctic Amplification. Previous research has shown increasing poleward advection of moisture from mid-latitudes, and increasing evaporation as a result of increasing temperatures, leading to increasing humidity or ‘humidification’. However, these patterns are not uniform across the circumpolar Arctic, requiring investigation at the regional level to better understand mechanisms and impacts in the complex Arctic climate system. Research on precipitation in the Arctic is notoriously difficult due to a dearth of long-term scientific observation stations. As such, we utilize ECMWF’s ERA5 reanalysis dataset to explore changing climate on Alaska’s Yukon-Kuskokwim Delta, where increasing temperatures and changes in summer precipitation patterns are altering surface moisture balances, which have consequences for tundra wildfire potential and subsistence food activities.

Analysis on the Yukon-Kuskokwim Delta in southwest Alaska establishes a regional baseline climatology and reveals several changes in the local hydrometeorology during the warm season (May–September) for 1982-2022. The YK-Delta region receives approximately 350 mm of rainfall, with August and September as the wettest months of the season and year. Precipitation originates from either large-scale systems (65%) or convective systems (35%). Large-scale precipitation arrives from either the Bering Sea (~44 storms per season) or Gulf of Alaska (~40 storms per season). No strong trend emerged for total precipitation over the 41-year study period (-17 mm/41 years), however, there is a split between declining large-scale precipitation (-41 mm/41 years) and increasing convective precipitation (24 mm/41 years). The decline in large-scale precipitation is supported by declining storm counts in the Bering Sea (-4.6 storms/41 years), though storm counts for the Gulf of Alaska show little change (-0.26 storms/41 years), as well as declining vertically integrated moisture convergence and moisture flux into the region from outside the study boundary. Declining trends in large-scale precipitation and increasing trends in convective precipitation are shifting the ratio of convective precipitation to the total by more than 10%, indicating an increasing importance of the local hydrologic cycle. This increasing importance is further supported by the significant increase in evaporation (32 mm/41 years, 95% sig) and specific humidity (2.5 g/kg/41 years). Despite increasing evaporation, there appears to be little change in relative humidity (-0.5%/41 years).

Changes to the surface moisture balance can impact wildfire regimes and subsistence food security. In the spring of 2022, the YK-Delta burned a record-breaking 1.3 million acres driven by a long and dry spring due to early snow-off dates. The potential for lightning-ignited tundra fires on the YK-Delta increases especially early and late in the growing season, when vegetation is dry from earlier snow-off dates or increasing summer evaporation. Increasing convective precipitation can indicate an increase in potential for tundra wildfires due to higher lightning strikes on the YK-Delta. Tundra wildfires are an understudied topic in Arctic climate change, as most of the fire weather research focuses on boreal regions, however, the notable increase in acreage burnt on the YK-Delta since 2015 is concerning and requires robust regional climate analysis to support future regional fire weather predictability and tundra wildfire management efforts. Near-surface hydrometeorology and trends during summer months are especially impactful on traditional food gathering and preservation methods for Yup’ik communities, who are indigenous to the Yukon-Kuskokwim Delta and have been subsisting off the land for thousands of years. Yup’ik elders with Calista Education and Culture, Inc., have discussed how increasing moisture in the air can hinder traditional fish drying methods, leading to rotting fish and loss of nutritional country food. Deeper investigation of regional atmospheric moisture changes, particularly seasonality changes, and understanding of impacts in the Arctic from community perspectives are invaluable for creating relevant and useful scientific research.