Streamflow Models in Southeast Alaska

Stream dynamics in the dramatic topography of Southeast Alaska are expected to shift over time with changes in climate. Resource managers and civil engineers need finer scale, more accurate models that predict changes in flow for small, ungaged watersheds in order to make important infrastructure planning decisions.

The AK CASC and collaborators from Oregon State University are working closely with agency partners to create predictive stream discharge models for Southeast Alaska watersheds.

Why are we doing this?

• Freshwater flow dynamics in Southeast Alaska are shifting over time with seasonal changes in precipitation and air temperature. Winter precipitation is increasingly falling as rain instead of snow, and extreme events such atmospheric rivers are increasing in frequency and severity.
• Understanding changes to streamflow is essential for infrastructure planning such as culvert replacement, bridge design, hydropower development, drinking water reservoir location identification, and floodplain restoration. Projections of peak flow are particularly important for culvert and bridge engineering, while seasonal variation and low flows may be more significant for hydropower and fish habitat restoration planning.
• Resource managers need better models for small, ungaged watersheds, and future flow models for all watersheds for planning purposes. Typically, most long-term gages are placed on larger rivers, creating inaccurate predictions for smaller streams, and the resolution of most global climate models of future weather is too coarse to capture the spatial variability across the Southeast Alaska landscape.

Approach

In the first phase of this project, AK CASC Fellow Rick Lader used a process called downscaling, which takes coarse, global-scale climate models and combines them with local weather data and physical factors like coastlines and elevation to create high-resolution climate projections. Lader has produced detailed models of the Northeast Gulf and the North, Central, and South Panhandle climate divisions over the period from 1981 through 2060. The dataset includes daily climate information at a 4-kilometer resolution, and for several selected watersheds, 1-kilometer resolution. 

The second phase of the project will be led by Dave Hill of OSU, who will incorporate Lader’s predictive climate modeling into his existing coastal river discharge model. This model estimates river discharge based on climate information as well as physical landscape factors.

End products

• A high-resolution (4 km) climate model for Southeast Alaska, including future scenarios
• Predictive stream discharge models for Southeast Alaska watersheds
• A searchable online map with past, current, and predicted streamflow information

Partners

Oregon State University, USFS Tongass National Forest, NOAA National Weather Service, Alaska Department of Transportation & Public Facilities