Understanding future projected changes and historical trends in extreme climate and streamflow events in warm boreal permafrost basins of Interior Alaska

Abstract:

Changes in future and historical extreme events may have disastrous consequences in vulnerable systems such as the warm- permafrost-dominated Interior region of Alaska. This paper presents a study examining extreme hydro-climate events (temperature, precipitation and streamflow) in Interior Alaskan watersheds, focused on results from Fairbanks, Alaska, located within the Chena River basin. Results are presented for an ensemble of global climate models (GCMs) and emission scenarios, run through to 2100. GCMs, selected for performance over the Alaskan domain, project the largest increases in minimum daily minimum temperature (TNn), compared to maximum daily maximum temperature (TXx), in the winter and spring at the Fairbanks Airport station. The increases in TNn and TXx are much larger (two to four times) than the across GCM standard deviations, indicating robustness in the projected changes. Statistically significant increases in five-day maximum precipitation are also projected to occur by the 2080s, with the largest increases expected for the summer and fall seasons. Streamflow projections provided by running the Sacramento Soil Moisture Accounting model, coupled with the SNOW17 snow model, are analyzed using a generalized extreme value (GEV) theorem and nonparametric trend approach. The Chena River basin exhibits linear nonstationary increases in maximum and minimum annual streamflow projected by the 2080s under both the RCP 4.5 and RCP 8.5 scenarios, minimized by the Akaike Information Criteria statistic, corrected for small sample sizes. Changes are indicative of increased flow volumes in the summer and fall, following precipitation changes projected to occur during these seasons. These changes are distinct from trends and GEV analysis performed on the historical streamflow series, which indicate declining flows associated with the loss of snowpack observed as a statistically significant reduction in relative flow volume (-49%, p-value 0.01) during the May-June period for the Chena River. These results paint a compelling picture of shifting ecosystems and future changes to water resources that may pose risks to ecology and infrastructure in the region.