River ice and open water extent from satellite imagery, Copper River Basin, Alaska (1973-2022)

The datasets included here were used to assess trends and geospatial patterns of river ice extent in the Copper River Basin of southcentral Alaska. Our goals were to document how river ice travel and wintertime access to traditional lands have been impacted by climate change, to support safe ice travel by identifying reaches with persistent open water vs early ice cover, and to understand the physical drivers of the local variation in freeze-up. Trends in ice extent for a section of the Copper River were analyzed using Landsat imagery from water years (WY, Oct. 1-Sep 30) 1973-2021. The direct observations of ice extent classes from each image date are provided (IceExtent_DirectObs.csv). These observations were gap-filled and summarized on a weekly basis, along with local air temperature metrics (IceExtent_AirTemps_Weekly_GapFilled.csv). Geospatial patterns of ice and open water extent for recent winters were assessed in two ways. First, we quantified reach-level late-winter open water extent of the Copper and Chitina rivers by digitizing Sentinel-2 multispectral images from WY 2018, 2020, and 2021, and combined these with river hydrologic and geomorphic characteristics (e.g. unit stream power, number of channels, river width, etc.). These data are provided in spatial (RiverReachData_Spatial.zip) and tabular (RiverReachData_Tabular.csv) formats. Second, we analyzed the progression of freeze-up by visualizing Sentinel-1 SAR imagery and compositing pixel-based classifications of water for Nov-Feb of WY 2018-2020 to show the seasonal and multiyear water occurrence (% season) (waterOccurrenceYYYY.tif, waterOccurrenceMultiYear.tif). The script for this SAR analysis in Google Earth Engine is provided (RiverIceAndOpenWater_SAR.js).