A tale of two flooded cities
Photo: Toronto, Canada, July 8, 2013 ©Bunton & Peel
Last summer disastrous floods caused by heavy rains hit both Calgary and Toronto, two of Canada’s largest cities, within a matter of weeks of one another.
Media coverage of the events at the time provided Canadians an arresting split image that captured the impact of extreme weather on urban environments.
Calgary’s Saddledome, home to the city’s NHL team, was flooded, along with the grounds of the iconic Calgary Stampede. In Toronto, thousands of commuters were left stranded at rush-hour as water inundated the city’s subway system and washed out major roads like the Don Valley Parkway.
A year onwards, a new book, Flood Forecast: Climate Risk and Resiliency in Canada (Rocky Mountain Books), incorporates eye-witness accounts and personal narratives of these events along with expert analysis and commentary to look at what cities need to do to act on climate change.
The authors, Robert William Sandford and Kerry Freek, discuss their new book and why cities need to better understand and respond to climate risks.
Your work looks at the larger relation of climate change to the water cycle in terms of understanding why extreme weather events are increasing. With a warmer climate why will we see more flood conditions?
(Sandford): The fundamental laws of atmospheric physics decree that a warmer atmosphere can hold more water vapour. The Clausius-Clapyron Relation provides that for each degree Celsius the temperature of the atmosphere warms, it will hold seven percent more water vapour. Established principles of fluid dynamics also decree that if you put energy into a fluid system it becomes more turbulent.
It appears also that the loss of Arctic sea ice is altering the behaviour of the Northern Hemisphere jet stream, slowing west winds, causing the jet stream to be wavier and to move more slowly, allowing weather systems to persist in places longer.
Add it all up and you have more water vapour available in the atmosphere to fuel bigger storms of greater intensity and longer duration. Expect this trend to continue as the global atmosphere continues to warm.
What were the hydro-climatic circumstances behind the flooding in Calgary and southern Alberta, and what can we learn from them to be better prepared?
(Sandford): In order to be better prepared for extreme weather events of greater intensity and longer duration we first have to accept that the global hydrological cycle has been affected by changes in the composition of the atmosphere.
Water now moves more energetically through that cycle, marking the end of a period of relative climate stability that we have enjoyed over the past two centuries. This means that the math we have used to date in the design of our built environment is not adequate to the new range of conditions that are emerging.
As the climatic circumstances to which we have become accustomed are not going to return during the lifetimes of anyone alive today, we have to learn to adapt to greater extremes. We do that by reducing further impacts on the hydrological cycle through wiser land-use management and by minimizing further human effects on the composition of the atmosphere by controlling harmful emissions.
We will also have to design infrastructure to higher standards, rethink our cities, and in some cases move out of harm’s way.
You describe Toronto’s flooding as a moment where the city came to understand its “flawed urban composition.” What have our efforts in planning and designing the built environment, especially in the last 100 years, overlooked or simply just got wrong when it comes to water?
(Freek): To say we have a flawed urban composition, I think, doesn’t necessarily infer mistakes were made. The people who designed cities 100 years ago couldn’t have predicted the extreme weather we’re having today. They designed the built environment with the knowledge they had at the time. A hundred years ago, combined sewers seemed like a good idea. What is it they say about hindsight?
Things have changed incredibly since that time. Cities are growing at a rapid rate. We’ve been told to expect more frequent and extreme wet weather. Urban growth plans have to take this knowledge into meaningful consideration.
But it’s certainly not that easy. Not only do cities have to face the reality of a changing climate and a growing demand on existing systems, they must contend with massive municipal infrastructure deficits, sunk costs in legacy systems, and the politics of development.
This combination of challenges can make moving toward resiliency a very, very slow process.
One of the experts you quote describes the flood Toronto experienced as only “dodging a bullet.” If cities are in need of becoming more resilient to future and increasingly more costly extreme wet weather events, how do they do it? How do you define resiliency?
(Freek): We may be seeing costly damage from extreme and frequent wet weather events, but the truth is flooding is a natural phenomenon — it’s part of the cycle. Simply put, when we interrupt the natural flow of water by building cities and other “human systems” in its path, that’s when we have a problem. In the past few months, Canadians have seen incredible loss.
A truly resilient city is one that works with, rather than against, nature. Resiliency doesn’t mean we can’t have buildings and structures. We must, however, have respect for water when we’re deciding where to build. It means taking into account the laws of nature and listening to our scientists. Future urban design will incorporate ways to be resilient — that is, adapt to new circumstances — and give floods a place to happen.
Micheal Fountain (micheal.fountain@aecom.com) is a communications manager with AECOM.