Extreme rainfall
On a global scale, there is consensus across the scientific community that there is a trend of increasing extreme rainfall. However, at the local scale, it’s harder to detect this trend in extreme rainfall with a short duration.
Changes observed on a global scale
By averaging the data globally, an increase in extreme rainfall is observed, particularly in annual maximum one-day rainfall.
Changes observed in Quebec and Canada
The most recent analyses of rainfall records suggest an increase in short-duration extreme rainfall events (5 minutes to 24 hours) in several regions of Canada. This trend, which had not been observed before, is partly explained by the inclusion of additional rain gauge stations and several years of new data. The use of a regional approach, pooling data from several stations in a region, also helps detect these trends.
The difficulty of finding trends in extreme rainfall observations
Several factors explain why it is difficult to identify past trends in extreme rainfall series from data recorded at weather stations in Canada:
Extreme rainfall events are rare and can be very localized, like summer thunderstorms. This means local rain gauge stations may not detect them.
The intensity of extreme rainfall varies greatly from one year to the next. Some years may experience exceptional extreme rainfall, while other years may have significantly less.
To detect these trends, very long data series and a significant number of rain gauge stations are required. However, in Canada, reliable precipitation archives only cover a few decades, and the number of stations remains small considering the surface area. Moreover, the majority of rainfall stations are concentrated in the southern part of the country, making coverage uneven.
