Identifying Resilient Headwater Streams to Mitigate Impacts of Future Drought in the Northwest

Streams are classified as perennial (flowing uninterrupted, year-round) or intermittent (flowing part of the year) or ephemeral (flowing only during rainfall events). The classifications of “streamflow permanence” were primarily established in the middle 20th century and are often outdated and inaccurate today if they were not adjusted for changes in land use, wildfires, or climate.Understanding where streams are perennial is important for a variety of reasons. For example, perennial streams receive special regulatory protections under a variety of statutes, and provide important habitat for fish, wildlife, and other species. To predict the likelihood that streams are perennial, we compiled nearly 25,000 observations of wet/dry conditions in streams across the Pacific Northwest from various state and federal agency databases. Field collection of those data alone would cost many millions of dollars. Processing of these data and the spatial environmental data to predict the likelihood that streams are perennial required several innovative steps with data processing and statistical analyses. The end products from this effort are peer-reviewed and publicly available regional datasets, models, and maps of where perennial streams are across the Pacific Northwest and how they respond to year-to-year variation in climate conditions, such as annual snow and rainfall. By engaging managers throughout the life of the project and presenting model findings in numerous forums, we are confident our products will be directly applied by managers and the general public to address water availability in the context of drought and other climate-related changes in the region.