PSU research supports Portland efforts to plan for climate change impacts on rainfall
Author: Christina Williams
Posted: April 9, 2018

While there is little debate that climate change is going to affect Pacific Northwest weather, many questions remain on how exactly it will play out. While some evidence suggests that incidents of intense and heavy rainfall may increase at the local level, there is still a need for a better understanding of how much of an increase and during what times of the year.

For the City of Portland’s Bureau of Environmental Services, those questions have specific ramifications in terms of stormwater management and how to keep the city running efficiently during times of heavy rainfall.

Which is why when Nick McCullar, civil engineer at BES heard Paul Loikith present a novel research method at the 2016 Northwest Climate Conference at Skamania Lodge, he was intrigued.

“The big question I had at that time was how do we downscale global climate model results to a high enough resolution that we can use them for our local decisions,” McCullar says. “Paul was talking about a way to do that.”

Loikith, assistant professor of Geography at Portland State University and director of the Portland State  Climate Science Lab, has focused his research on a novel way to look at local extremes in global climate models. His method identifies the key weather patterns that drive local extreme events as observed by a high-density network of local rainfall gauges. Then, changes in these weather patterns can be assessed in freely available global climate model simulations of future climate produced by labs around the world.

“The challenge is that most state-of-the-art climate models are limited when it comes to resolving local extremes because their grid resolution is too coarse. This is particularly acute in a place with complex and influential topography like Portland, said Loikith.

Loikith is a Faculty Fellow of the PSU Institute for Sustainable Solutions (ISS), which serves as a platform to organize effective community-university collaboration that results in a more sustainable region. ISS helped connect Loikith with the City of Portland and provided funding for the initial research project with BES.

The goal of the project is to answer questions around extreme precipitation events—we might call them downpours—such as how often Portland can expect to see them in the future, how their occurrences might change seasonally, and similar questions.

Paul Loikith and Christina Aragon Working with graduate student Christina Aragon, Loikith is using a machine learning technique called Self-Organizing Maps to identify a range of different weather patterns that are historically associated with extreme precipitation in the Portland area and classifying their differences and characteristics. Aragon is writing and working with code that can sort vast amounts of weather data to find the relevant patterns and create maps and graphics to show trends.

“The goal is to use the meteorological patterns identified in our research to evaluate climate models and potential changes that are linked to various water resources,” Aragon said.

What’s exciting about the methodology is that it is easily replicable and scalable for other regions.

“As engineers we would really, really like to have one number that we can plan for, but with climate change there is so much uncertainty,” McCullar says. “If Paul’s research can show us that we’re likely to see a 10 percent increase in one particular kind of storm, that’s really helpful information.”

While BES’s main concern is in dealing with potential sewage overflow events, Loikith is also talking to other City of Portland departments about how his research might be helpful in planning for other potential climate change-related challenges. He’s also one of the ISS Faculty Fellows working on the Clackamas River Watershed Resilience project, which is focused on long-term water planning for the region.

Loikith, whose background is in atmospheric science, joined Portland State in 2015, after doing post-doctorate work at Caltech’s NASA Jet Propulsion Laboratory in Southern California. He was attracted to Portland by PSU’s focus on interdisciplinary work.

“That was a major attraction for me,” he says. “Here you are encouraged to try different things and work across disciplinary boundaries.”

As for the weather, Loikith points out that Portland’s steady-rain winters followed by temperate summers doesn’t offer the weather variety of his native New Jersey.

“The weather here,” he says with a smile, “is actually pretty boring.”