Compilation of Historical Water Temperature Data for Large Rivers in Alaska using the Landsat Satellite Archive Active

Water temperature is one of the key elements of freshwater ecosystems and is a critical element within natural resources monitoring programs. In Arctic and sub-Arctic rivers, water temperature especially relates to the physical and biological features of a river, as it affects how rivers interact with portions of the landscape and the life cycles and composition of stream life and ecosystems. This was emphasized in 2019, when unseasonably warm water within Alaska’s large rivers triggered heat related mortality in large numbers of salmon before they could reach spawning grounds. Despite the importance, systematic and extensive water temperature data are difficult to capture and are historically lacking for large Arctic and sub-Arctic river systems.  

In the absence of local measurements, remote sensing techniques can provide an indirect measurement of water temperature over time and space. Remotely sensing water temperature in large Alaska rivers is a valuable tool for multiple reasons. Thermal infrared radiation emitted from water surfaces can be measured by satellite to provide efficient estimates of water temperature over broad regions. Furthermore, these estimates can supplement existing hydrologic monitoring systems such as USGS stream gages. While stream gages collect accurate measurements, regionally explicit heat maps can depict important variation in water temperature caused by river currents and cold- or warm-water contributions from other water sources, which is critical information for identifying areas of favorable habitat conditions for salmon. 

This project will extract and compile historical heat maps of water temperature within the Yukon, Tanana, and Kuskokwim Rivers in Alaska using satellite-derived estimates. Heat maps will be for the ice-free season between 1985 and present and can be summarized for areas of interest to build historical temperature records as needed. In the event stream gage data are disrupted due to technical or environmental factors, satellite estimates could help fill data gaps. With an ever-growing archive of historical satellite images, water temperature records can be extended back in time to provide greater context for contemporary records and allow for time series analysis in a region experiencing particularly rapid climate change.