How the Tree Canopy Protects Urban Stream Health: "The right trees in the right places intercept rainfall", says IGP Co-Chair Richard Boase
Context for Research Initiative
The District of North Vancouver, District of West Vancouver, and City of North Vancouver are founding members of the Inter-Governmental Partnership that developed and maintains the Water Balance Model for British Columbia.
Commencing in 2005, the three North Shore municipalities partnered with the University of British Columbia and others to implement a precedent-setting project to quantify the ‘rainfall capture benefits’ of the urban tree canopy.
“This project is a ‘North American first’. The research results are informing development of a Tree Canopy Module for the Water Balance Model. The module is expected to be completed by the end of 2010,” states Ted van der Gulik, Chair of the Inter-Governmental Partnership (IGP).
“While considerable research has been undertaken in forest stands in the natural environment, very little had been done in an urban setting anywhere in North America,” adds Dr. Markus Weiler, former Chair of Forest Hydrology at UBC. He provided scientific oversight for the project.
“One of our research interests was to determine the effectiveness of a single tree 
versus that for a cluster of trees. We explored and quantified the variables influencing the interception process. We also investigated the effects of tree density, tree structure and tree species on rainfall interception,” explains the District of North Vancouver’s Richard Boase. He is IGP Co-Chair.
To learn more about the inter-governmental partnership with UBC, click on UBC Tree Canopy Research Interception Project.
Trees Intercept Rainfall
“Trees can intercept upwards of 50% of the rain that falls each year on a watershed. Removing the tree cover means that more and more rainfall is converted into runoff volume,” states Richard Boase.
“A quantum increase in runoff volume then impacts stream and watershed health. The impacts are cumulative consequences of repeated erosion and sedimentation.”
“On the North Shore mountainside, potentially doubling the runoff volume has major implications for rainwater and watershed management. Only so much rainwater can be infiltrated naturally or forced unnaturally into the ground. We need trees to reduce the proportionate volume of rainfall that eventually becomes runoff.”
“This need was a driver for the three municipalities collaborating to implement the 
North Shore Tree Canopy Interception Research Project (2006-2010) in partnership with UBC and others. The research has quantified the proportion of rainfall intercepted by the tree canopy in an urban setting.”
“The research has provided a science-based understanding about the benefits of maintaining a tree canopy in the urban environment. This understanding will inform stream health protection strategies on the North Shore and elsewhere. Soon, these findings will be incorporated in the WBM to populate a new Tree Canopy Module.”
“At the end of the day, it is all about ensuring that the right trees are in the right places to protect stream health AND enhance community liveability,” concludes Richard Boase.
Beyond the Guidebook 2010
The story of the Tree Canopy Interception Research Project is included in Beyond the Guidebook 2010: Implementing a New Culture for Urban Watershed Protection and Restoration in British Columbia, released in June 2010.
“Beyond the Guidebook 2010 provides local governments with ‘how to’ guidance for developing outcome-oriented urban watershed plans,” states Corino Salomi, Lower Fraser Valley Area Manager with the Department of Fisheries & Oceans.
“Rainwater management has a bigger picture. It is not just about drainage. Non-point source pollution, species at risk, ecosystem functions, and drought management are all coming to the forefront. Everything is linked. So, watershed targets and land development solutions must be holistic in scope.”
Posted June 2010