It's sunny in downtown Montreal and pouring rain at the airport. Such events will be more likely in the future.

The climate of the city is changing and will continue to do so at a rapidly increasing rate and with much more spatial variability in the future.

That's according to new research from Concordia's Department of Building, Civil and Environmental Engineering.

MASc student Pablo Jaramillo and assistant professor Ali Nazemi recently published a study on water security in Sustainable Cities and Society. In it they set out to test the reliability of NASA's downscaled climate data set, the NEX-GDDP, as a tool for accurately modelling long-term annual climate impacts on the scale of a city.

Using the Greater Montreal Area and its neighbouring regions for their case study, the researchers compiled observed data recorded at eight local weather stations from 1950 to 2006. They then compared it to data yielded from the NASA data set for the same period and common temporal and spatial scales.

They found significant trends in the city's climate, which can be captured fairly well by the downscaled data.

advertisement

Comparing the projected trends from 2006 to 2099 with past observed trends, they showed that the Montreal region's climate will continue to change at a faster, more intense rate and with more pronounced spatio-temporal variability.

"This means that we will see more differences in the long-term climate over the Island of Montreal and its neighbouring regions," says Nazemi, the study's lead researcher.

"We can clearly see more variability in climate characteristics, such as extreme rainfall and temperature, as well as the number of days with extreme hot or cold temperature over the same region."

'One-size-fits-all will no longer be feasible'

According to Nazemi, this finding will have huge implications for urban management.

advertisement

"Climate plays a key role in the design and operation of urban infrastructure and to a large extent determines water and energy demands. As a result, changes in climate conditions will have direct impacts on how we design almost any aspect of the city, from its drainage system to its energy use," he explains.

"Most of the time, we consider a single value in relation to the design of these systems and we assume that this value will remain unchanged during the infrastructure's lifespan, Nazemi adds.

"We already know that this is not the case anymore due to climate change; but as the spatial variance in the projected changes in our climate also increases, the current approach of one-size-fits-all will no longer be feasible. For instance, a sewage system designed to prevent flooding in downtown Montreal may fail to prevent flooding in Dorval."

Accordingly, one of the main takeaways of the study is that urban management should move toward local design and management as opposed to city-wide solutions to climate change impacts.

In addition, while the findings confirm that downscaled models can reproduce observed rates of change in the historical climate of a city, the discrepancies in the long-term climate conditions limit the applicability of the downscaled climate projections.

For Nazemi, this points to the need for more robust technology for the assessment of climate change impacts at the local level.

"Whether the downscaled climate projections can adequately inform climate impact assessments in a city like Montreal depends on the type of management problem and the resulting decisions," he says.

"Because of some limitations, we advocate considering more holistic frameworks. These approaches should ideally be applied in conjunction with acclaimed top-down approaches to support climate change vulnerability assessment in Montreal until improved climate modelling capability becomes available."