High water and flooding
The evaluation of trends is complex
Due to non-climatic factors, it is difficult to detect trends in the observed flood regimes. Firstly, flow observations are obtained from the many gauging stations spread across Quebec. The quality of measuring instruments over time and between stations influences the results. Finally, changes in land use over time can affect the hydrology of a watershed.
The high natural variability of this hazard also makes it difficult to detect significant trends on a provincial scale. As illustrated in the figure below, the variation in maximum spring discharge at a measuring station on the Batiscan River is highly variable from one year to the next. It is therefore more difficult to establish correlations or observe conclusive trends on many Quebec rivers. What's more, the historical series of flow data taken at hydrological stations is too short to obtain obvious trends.
Figure 1 : Series of maximum spring flows at the Batiscan River 050304 station, from 1968 to 2021. (From: MELCCFP, 2023)
Spring freshets arrive earlier
Nevertheless, a trend has been detected regarding spring freshets: on average, they occur earlier in the season at nearly a quarter of the stations analyzed. This trend is particularly observed in stations located north and east of southern Quebec. It should be noted, however, that the current data does not indicate whether these earlier spring freshets generated flooding.
