PSU research helps city better understand climate change's impact on vital Bull Run Watershed

The Bull Run Watershed is Portland's primary source of drinking water for more than 950,000 residents in the metro region — and new research from Portland State's Climate Science Lab will help the city better understand how climate change will impact the watershed and affect future water supply and quality.

The two-year project was a collaboration between the Climate Science Lab, led by assistant geography professor Paul Loikith, and the Portland Water Bureau. The findings will inform water resource and water quality management.

The team studied storm types that historically have produced heavy precipitation — downpours — over the watershed, which can cause water quality challenges due to runoff of sediment into the reservoir system. Loikith, who is also a faculty fellow for PSU's Institute for Sustainable Solutions, said research results suggest that while future storms will occur in a much warmer environment than today as temperatures continue to rise, there's little evidence of major changes in the frequency or intensity of storms known to be associated with heavy precipitation over the watershed.

The team also analyzed projected changes in a type of weather pattern, referred to meteorologically as an atmospheric ridge, in the springtime. Atmospheric ridges typically bring drier and warmer-than-average temperatures, and recent springs have seen an unusually high number of days with ridging. Such unusually dry and warm conditions can bring an early end to the rainy season and an early beginning to Bull Run reservoir drawdown. Loikith said that while results do not point to a drastic change in the prevalence of springtime ridges in the future, temperature-related impacts under ridging will become more severe.

The Portland Water Bureau will use the team's findings to plan for a range of future water supply conditions. The bureau said it's preparing for how warmer temperatures could affect the timing and length of Bull Run reservoir drawdown during the high-water demand season and how to meet water supply needs amid changing conditions. 

This project supported the work of two graduate geography students, Christina Aragon and Graham Taylor, and an undergraduate physics student, Ellen Koukel.