Soaking Up Storms

 by Megan Clendenan

Where I live, in the Pacific Northwest, autumn means rain and plenty of it. The rain pours down and flies sideways, soaking your cuffs and everything else if you’ve forgotten an umbrella.

If you’re out walking during a storm in a city, you might notice rainwater soaking the streets, skidding across parking lots and sidewalks and then pouring into drains – if they aren’t clogged by soggy leaves or other debris. All that storm water draining into the sewer mixes with oils, heavy metals, pesticides and other pollutants that are on our roadways. In cities, where impermeable surfaces such as concrete sidewalks, roads and parking lots are common, a significant portion of rainfall ends up in the sewer system alongside whatever chemicals it has picked up along the way. Then, depending on the city’s location, it runs into nearby waterways, lakes or oceans.
 

With rising global temperatures and changing weather patterns, more than 50% of the world’s population now reside in cities, on the front line of climate change. How can cities cope? One strategy is to learn from nature, and adapt urban buildings, infrastructure, and surfaces to work with the surrounding ecosystem.
 

Take Seattle, Washington, a city with significant annual rainfall. In 2017, a nonprofit group called Urban Greenprint teamed up with engineers, biologists, and city planners to study how they could design buildings and infrastructure to help mimic the evaporation rate of the Pacific Northwest forest to help reduce flooding as well as reduce polluted runoff from washing into the nearby Pacific Ocean.

 

Can you count all the layers? Photo by Megan Clendenan

The forest consists of thousands of layers, which work together to slow the rain and retain moisture before it reaches the ground. Moss and tree bark can hold water like a sponge. Douglas fir trees, common to the area, have needles that spear raindrops, breaking them into smaller parts, increasing the amount of evaporation and decreasing soil erosion.
 

With thoughtful design, urban buildings and other infrastructure can mimic layers found in the forest. Living walls can slow rainfall as it moves from the roof, through the textured green wall, absorbing moisture during each stage of the process. Canopies, awnings, screens and wire sculptures can mimic the ability of pine needles to split raindrops and increase evaporation. Green rooftops and ‘rain gardens’ planted next to sidewalks can soak up water like sponges.

A rain garden next to a sidewalk also shields pedestrians
from the cars. Photo by Megan Clendenan

So next time I’m out during a big rainfall, I’m going to keep my eyes open for places where my city is soaking up the storm – and where adaptations could be made.

Design Concepts Learned from Pacific Northwest Forests, Urban Greenprint, Seattle
https://issuu.com/urbangreenprint/docs/urban_greenprint_seedkit_v1
https://www.asla.org/climatemitigation.aspx
https://www.nrdc.org/stories/green-infrastructure-how-manage-water-sustainable-way