We documented the historic changes in local river ice seasonality as it relates to over-ice travel and characterized the geospatial patterns and drivers of open water hazards on the Copper River in Alaska with remote sensing.
We found large declines in weekly river ice extent related to increasing air temperatures over the last ~50 years that negatively impact winter access to land and subsistence resources. Spatial variation in reach-level hydrologic characteristics created a mosaic of ice conditions that differs in freeze-up timing and open water occurrence.
Climate-driven changes in high-latitude river ice regimes present new challenges to people who depend on the ice cover for winter travel and access to resources. This study focused on the Copper River basin of southcentral Alaska, where residents have expressed concern about major changes in river ice conditions. We used satellite remote sensing (optical and synthetic aperture radar, SAR), validated with community observations, to document the historic changes in local river ice seasonality and to characterize the geospatial patterns and drivers of open water hazards. We found a substantial decline in the weekly probability of extensive ice cover in the last ~50 years (53.3 (± 6.6) percentage points) due to increasing air temperatures. Changes included delayed or incomplete freeze-up and early break-up. We mapped geospatial variation in freeze-up and open water occurrence, patterns that appear to be driven by flow energy, channel form, and the bi-directional effects of ice flow and accumulation, and differentiated potential winter river crossing areas from hazardous open water zones. The results of this study are intended to support decision-making and adaptation in response to rapidly changing river ice conditions.