Anyone who has lived in the Pacific Northwest for some time is acutely aware that the intensity of rainfall events has dramatically shifted due to climate change. When I moved to Portland in the 1990s, the default was a constant, misty drizzle, which has now been replaced at regular intervals with a winter full of torrential downpours amongst a slew of other climatic shifts like hotter summers and significantly colder and snowier winters.
An occasional ‘Pineapple Express’ or ‘Chinook Winds’ were outliers, with occasional wet periods caused by shifts bringing warm air and moisture from the Tropics to northern latitudes. These, we know now, are a form of an atmospheric river, a term from the 1990s that has re-emerged as a new addition to our new climate-change-focused lexicon. Atmospheric rivers are water vapor channels in the atmosphere, which can be up to 300 miles wide and over 1000 miles long, typically occurring in the mid-latitudes.
These storms are part of the water cycle, providing a range of positive benefits and negative impacts. Positively, they can help reduce drought and increase snowpack which can help reduce wildfire risk. The negatives result in too much water, too quickly, causing flooding, mudslides, and other damaging impacts. Researchers have been developing methods to predict atmospheric rivers to prevent some of these negative consequences. They have developed a scale ranking the intensity and danger from AR1, noting a weak system that is “primarily beneficial” up to AR5, which is noted as “primarily hazardous.”
The cycle and intensity of atmospheric rivers will continue to change along with our changing climate, and the water vapor stored in these systems will increase with the continual rising temperatures of the global air and ocean systems. This will mean longer seasons of rainfall, more intense storms, and the need to reconsider our approaches to stormwater management that worked a decade ago but may be falling short.
Connections to Hidden Hydrology
A recent op-ed piece “Comment: Atmospheric rivers require new approach to water management.” (Victoria Times Colonist, 09.31.24) by Alan Shapiro, an environmental consultant, and Tim Morris, director of B.C. Water Legacy, outlines how hidden hydrology can be instrumental in providing resilient green infrastructure for these atmospheric rivers, specifically by reversing the root causes of the problem and reducing resilience: originally removing steams from the urban landscape, paving surfaces, and draining wetlands. They note several ideas like “sponge parks” and well-tested green infrastructure solutions including “Green roofs, permeable pavement, and rain gardens mimic natural water processes by absorbing and filtering rainwater like a sponge before returning it to waterways.”
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The on-the-ground application of this idea can be found in Vancouver, British Columbia. This is highlighted in the article “B.C. atmospheric river a successful first test of community-led rain management project.” (CBC, 09.26.24) which describes the St. George Rainway and the performance of this green infrastructure system during recent extreme rainfall events. I wrote about this project earlier this year, “Vancouver Rainways”, (05.03.24) where I described the goals of the project and the context of hidden hydrology in Vancouver. The recent article highlights the hidden hydrological connection, showing how the rainway follows the route of “an ancient, buried creek” that is a tributary of False Creek:
“The road and homes along St. George Street are constructed above a creek that historically emptied into False Creek. The creek still runs underground, through a series of pipes and culverts — where it hasn’t offered the community adequate drainage for at least a decade, often leading to street flooding and damage to the roadway.”
Daylighting the creek was not feasible due to the impacts on the neighborhood homes and infrastructure. However, the metaphorical river solution of rain gardens utilizes biomimicry principles to provide a linear landscape that provides many of the same benefits of the original creek corridor. The recent atmospheric rivers presented an opportunity to see the project in action where it accommodated large amounts of runoff from adjacent streets.
The ability to trace routes of buried streams provides us with a watershed-based framework to implement green infrastructure solutions that mimic the original hydrology. As you see from the map of Vancouver, B.C. we could start with numerous corridors, using linear green infrastructure solutions like St. George Rainway as a model following closely the street networks. These could be supplemented by larger solutions on public and private property to recreate the functions of wetlands, ponds or other water bodies lost to development over the years. Finally, green roofs and rainwater capture from adjacent buildings and permeable pavements could reduce runoff — finalizing the holistic, integrated strategy.
Hidden hydrology provides these strategies with a watershed-specific framework for green infrastructure that can provide community-wide resilience to extreme weather like Atmospheric Rivers. This is not meant to be full restoration and daylighting, often challenged by site constraints that make it overly expensive or impactful. Linear green infrastructure is a tool in the toolbox, mimicking the function of urban creeks and streams, providing the same benefits, including absorption of runoff, provision of habitat, urban cooling, and visual access to nature, all following the routes of our lost waterways.
Note: This post was originally posted on Substack on 11/11/24 and added to the Hidden Hydrology website on 04/22/25.