A New Approach in Measuring Rainfall Interception by Urban Trees in Coastal British Columbia
Innovation in Rainwater Management
“Rapid urban expansion, increased traffic, ageing infrastructure, greater climatic variability, and the need for enhanced sustainability of urban water resources pose significant challenges to conventional stormwater management,” states Dr. Hans Schreier of the University of British Columbia.
“Innovative approaches are needed in order to mitigate the risk of flooding, pollution, and aquatic ecosystem degradation, and enhance beneficial uses of urban waters.”
“To examine such approaches, a series of three regional conferences on innovative rainwater/stormwater management were held in Vancouver, Calgary, and Toronto during 2007 to 2008 under the sponsorship of the Canadian Water Network (CWN) and the Canadian Mortgage and Housing Corporation (CMHC).”
The programs for each of these regional events included a presentation on the Urban Forest Research Project that was implemented in Metro Vancouver during the 2005 – 2010 period. The resulting paper was co-authored by Dr. Markus Weiler and Yeganeh Asadian.
Urban Forest Research Project
In 2006, the City of North Vancouver, District of West Vancouver and District of North Vancouver formed a North Shore Inter-Municipal Coordinating Team (chaired by the District of North Vancouver) to implement a network of 60 tree canopy climate stations across the North Shore region of Metro Vancouver.
The Urban Forest Research Project was undertaken through a partnership with the University of British Columbia. The project received funding from the Province of British Columbia, Metro Vancouver, the Real Estate Foundation of British Columbia, and the Canada Water Network.
A New Approach
“Interception loss plays an important role in controlling the water balance of a watershed, especially where urban development has taken place. The aim of the Urban Forest Research Project was to illustrate the importance of urban trees as a form of ‘green infrastructure’ where they reduce rainwater runoff and rainwater intensity. In addition, trees cause a delay in precipitation reaching the ground,” states Dr. Markus Weiler, former Chair of Forest Hydrology at UBC. He was responsible for the developing the research approach.
“We studied the interception loss in the North Shore of British Columbia. We applied a unique methodology for measuring throughfall under six different urban trees using a system of long polyvinyl chloride pipes hung beneath the canopy capturing the throughfall and draining it to a rain gauge attached to a data logger,” continues Yeganeh Asadian. She completed the research and analysis in fulfillment of her Master’s thesis.
“We selected different tree species in variable landscape sites (streets, parks, and natural forested areas) and elevations to ensure that the system adequately captured the throughfall variability.”
“We monitored interception and throughfall over a one year cycle for which the results of seven discrete storm events for coniferous trees from the District of North Vancouver during 2007 to 2008 are presented in our paper titled A New Approach in Measuring Rainfall Interception by Urban Trees in Coastal British Columbia,” continues Yeganeh Asadian.
“Cumulative gross precipitation for seven selected events was 377 mm. Average canopy interception during these events for Douglas-fir and western red cedar were 49.1% and 60.9%, where it corresponded to average net loss of 20.4 and 32.3 mm, respectively.”
“Interception losses calculated for urban trees were approximately twice as great as those calculated for trees within natural forest stands. The identified controls on interception loss were meteorological factors, tree type, and health. The results were variable depending on location, tree health, and canopy structure.”
“The interspecies variation on interception was evident as western red cedar trees showed higher interception losses, longer time delays, and lower throughfall intensities compared with Douglasfirs,” concludes Yeganeh Asadian.
To Learn More:
To download a copy of the paper by Yeganeh Asadian and Dr. Markus Weiler, click on A New Approach in Measuring Rainfall Interception by Urban Trees in Coastal British Columbia.
For an overview of the papers presented at the conference series, click on Innovation in Stormwater Management in Canada: The Way Forward to download a paper co-authored by Hans Schreier and Jiri Marsalek, series organizers.