Examining Remotely Sensed Products Used in Operational Decision Support Services During the record breaking 2023 Alaska Ice breakup season.

Globally impacting human lives and properties, floods are the most frequent natural disasters. Accurate and timely flood mapping plays a significant role for disaster monitoring and relief efforts. Floods are generally short-term disasters with large extents, most of which are caused by extensive rainfall, snowmelt and ice jams. This makes remotely sensed data from satellites to have a great advantage in flood mapping because they can observe the big pictures of floodwaters. The optical satellite imagery from Low-Earth-Orbiting satellites (LEO) and Geostationary satellites (GEO) are especially advantageous in flood mapping because of their excellent data availability, large spatial coverage, and low cost. Synthetic Aperture Radar (SAR), providing all-weather, high-resolution flood mapping and is able to see flooding even during times of extended cloud cover, which inhibits optical flood detection. SAR imagery over flooded areas requires activation of the sensor and thus SAR sensors may not collect imagery even during a satellite overpass.

The 2023 Alaska Breakup season started typically with a snowpack a bit higher than long term climate normals but not extremely so. What made the spring of 2023 dangerous were a combination of factors, including a larger (and wetter) than average snow pack throughout the drainage basin as well as cold temperatures lasting longer than normal combined with a quick transition to average temperatures. The cooler temperatures left the river ice in the Yukon and Kuskokwim (the two largest rivers) with stronger ice resulting in a slower rate of decay of this ice. This, followed by a quickly melting snowpack resulted in a cascading series of ice jams down both rivers. All told, the state experienced two catastrophic class events (Circle on the Yukon and Crooked Creek on the Kuskokwim), three major floods, ten moderate level floods and fourteen minor flooding events. This presentation will show how satellite data, along with critical information from Riverwatch flights and information from villages and citizen scientists provided effective decision support during the 2023 Alaska breakup season.