Module 6: GI and Building Resilience For Climate Change

All municipal infrastructure is designed using statistical projections of likely weather patterns. To make a building or a bridge safe from floods you need to know how high the surrounding water may rise. To build a reservoir and a dam you need to know how much water will flow into it and how much water you need. To design a sewer well you need to know that it will not flood during an average spring storm. As climate change leads to changes in precipitation rates and depths around the world, infrastructure designed for the 20^th century will become obsolete. Cities that construct infrastructure pre-emptively, with projections of rainfall and heat, may end up spending too much on oversized systems. Or focus on the wrong issue altogether; planning for drought, when they should have been protecting from floods. Even the best global climate models (GCMs) acknowledge margins of error that represent trillions of dollars in infrastructure over the next hundred years.

Whether cities attempt to plan for a projected climate future or rebuild after failure, an unprecedented global reconstruction of infrastructure is likely at hand. This reconstruction is an opportunity to rethink how cities work and what they can provide for the growing number of people that call them home. Planning for this reconstruction well requires adaptable infrastructure designed not for a measured “what-has-been” but for a feasible range of “what-could-be”. This is green infrastructure’s greatest potential; a capacity for resilience that could help fortify cities against climate uncertainty while also reducing the emissions associated with development. The combination of these benefits is captured by the term “Low-carbon resilience (LCR)” (ACT, 2018). LCR focuses on solutions that simultaneously decrease GHG emissions while improving system resilience to climate change impacts. GI is a common entry point for municipalities to begin accounting for LCR in their planning decisions. Green infrastructure is a LCR entry point for local governments because GI interventions avoid or reduce the use of carbon-intensive products like concrete and steel that define grey infrastructure and require less carbon intensive construction techniques, while also improving system resilience to impacts like flooding and extreme heat temperatures. GI systems can also absorb carbon throughout their lifetime, potentially offsetting the emissions associated with their construction. A study of 28 U.S cities found that urban trees sequester an average of 2.05 t C ha^-1 year^-1(Demuzere et al., 2014). With proper maintenance, GI systems can become more effective with age as plant communities grow and establish (Denjean et al., 2017).

Successful design of GI systems requires a thorough understanding of local environmental and ecological conditions to determine the potential rates of rainfall, infiltration and evapotranspiration. If available, downscaled climate models should be considered to assess how climate change may shift these variables in the future. Locally available flora should also be considered when determining evapotranspiration rates and potential rates of pollutant removal through adsorption or biotransformation. Locally available soils should be accounted for when determining the target drawdown times and infiltration rates of GI systems. Locally available grey infrastructure components that contribute to GI functionality, such as perforated pipes, overflow inlet grates, inspection chambers, and pipe cleanouts must also be assessed and sourced. Collecting and analyzing this environmental, ecological, and industrial data represents a significant challenge for budget-constrained municipalities.

For traditional infrastructure, municipal responsibility has worked well. It is relatively easy to transfer traditional grey infrastructure design principles from one region to another. Even when accounting for changing rainfall patterns and climatic conditions, grey infrastructure can be designed and installed based on a few fundamental principles that govern the performance of constructed systems like roads, sewers, and building. GI must be designed to accommodate local context because it utilizes living components such as vegetation, soil biota, and local fauna which are essential to GI performance and success. A GI system designed for southern Ontario will use vegetation and soil from that region which may not be available in Vancouver or suitable for Vancouver’s climate. The living components of Green Infrastructure require each municipality to establish their own GI best practices that account for projected local impacts, existing vulnerabilities, and available ecological and biological resources.

Despite these challenges, resources are being developed around the world that other municipalities are learning from and using to decrease the burden of their own data collection. Municipalities pursuing GI are looking to cities within their ecological and climatic zones to coordinate on research projects and testing. For example, when selecting an appropriate soil for pollutant removal, municipalities can look to research undertaken elsewhere that uses soils with similar properties to those available locally (i.e. particle size distribution and organic content) to help inform the selection process.

In the context of climate change, physical system adaptability is defined by its capacity to handle the extremes that climate change may bring. The readings and other resources in this module provide insights and tools for discussing adaptation to climate change via GI and outline policies and practices that will require city leaders, in the language used in the Vancouver’s Changing Shoreline report, to either resist, accommodate, move or provide a combination of all three strategies.