Climate change could mean more massive downpours

That sump pump you rented to suck out the standing water in your basement? You might want to ask Santa to leave you one under the tree this year.

Record-setting storms like the one Sunday and Monday that flooded the Northwest could become more of the norm as climate change skews our region's rainfall patterns and leads to more of these massive deluges as compared to the typical drizzle.

It's not guaranteed, but scientists said that multiple computer climate models predict an increased likelihood of more rain -- and more episodes of heavier rainfall -- in fall and winter, less in the summer.

Monday Seattle logged nearly 5 inches of rain and scored the second rainiest day on record. First place still goes to a rainy day in October 2003.

"There is a risk under climate change of having more storms of this nature," said Eric Salathe, a research scientist with the University of Washington's Climate Impacts Group.

"Given that this is also a La Niņa year, I'd be very surprised if this is the last such storm you get up there this year," said Kelly Redmond, a climate scientist and interim director of the Western Regional Climate Center. The center, in Reno, Nev., is operated by the National Oceanic and Atmospheric Administration.

"The bigger question is whether the Northwest is seeing more of these kinds of events," Redmond said. "It isn't just a matter of increased rainfall. It's also about the form of that precipitation ... whether you are getting more 'typhoon' moisture out of the tropical regions."

Some contend it's no longer much in question. A study released Tuesday by the non-profit Environment Washington reported that storms with heavy rainfall are 30 percent more frequent in Washington now compared with 60 years ago. The analysis was done using data from weather stations.

"The thing that's interesting about this report is that certainly no single weather event can be tied directly to global warming, but the fact that we're seeing a greater frequency of these events is evidence of global warming in Washington state," said Bill LaBorde, program director for the environmental group.

"We've tried to let people be aware that there is this risk that has to be managed in some way," Salathe said.

Redmond and another colleague at NOAA, climatologist Jim Ashby, said their data does show an uptick in Northwest rainfall amount over the past 15 years. But both said it would be premature to try to draw any definitive conclusions as to a trend.

"There isn't really a firm pattern or trend yet," Ashby said. Ashby said 1950 is still the wettest year on record for the Pacific Northwest and the rainfall pattern is notoriously chaotic when viewed over the longer term.

"It's a very important question and there is some evidence to support the claim that rainfall is increasing in the Northwest," Redmond said. "It's possible. But the jury is still out on whether you are getting more of these warm, tropical moisture events."

Assuming the climate models, if not necessarily Environment Washington's hard numbers, are accurate in predicting more massive deluges, an important environmental question is how to control the downpour that flooded roadways and basements and scoured streams where salmon have been laying eggs in recent weeks.

Some engineers, scientists and environmentalists think there are ways to control stormwater runoff that helps people as well as fish, bugs, birds and other wildlife.

In the past, trees and plants would catch rain in their leaves and needles, allowing it to drip to the ground more slowly or holding so it evaporates. Once it reached the ground it was spongy with decaying leaves and needles. Streams weren't constrained and able to flood their banks.

When an area is developed, water runs from streets and houses into gutters and eventually into streams and Puget Sound, carrying with it oil, toxic metals and pesticides. A study by the Department of Ecology released Friday found that stormwater was the greatest pathway to carrying most pollutants to the Sound.

One option for dealing with the stormwater is building detention ponds that hold the water and release it slowly and allow it to soak into the ground.

But that alone won't solve the problem -- particularly with rainfalls like Monday's that dumped some 5.8 billion gallons of water on Seattle.

Could you build a detention facility at today's property prices and construction costs that could hold that much water? asked Bob Spencer, watershed stewardship coordinator for Seattle Public Utilities. "You just couldn't."

Projects such as the restoration of Thornton Creek at Northgate help a little bit. The creek is being unearthed from buried pipes to flow like a normal stream, albeit in a heavily urbanized setting. The creek is being restored with broader banks to hold more water during storms. But it won't do much for typhoon-type rains.

"Individual people can do things to improve the amount of impervious surfaces on their property," Spencer said. That means gravel driveways and patios made of paving stones instead of concrete. While costly, people can install green roofs that are covered in plants. Another less expensive option is a rain garden -- basically a deep depression lined with gravel and plants where water can collect and soak into the ground.

Seattle has received kudos for projects in select areas that increase natural drainage and reduce runoff by making streets more narrow and lined with water-absorbing ditches, using porous cement and rain barrels. Rich Horner, a research associate professor with the UW's Civil and Environmental Engineering Department has studied the projects.

"You can definitely cut down on surface runoff with these techniques," he said. "And you're going to cut down on flooding too."