Integrative Frequency Analysis

Expected climate changes in southern Québec include a decrease in winter snow cover and an increase in spring precipitation, which have opposing effects on spring floods. The intensity of the resulting changes varies with time and latitude. Furthermore, historic flow observations are rare: flow rates are not measured for the vast majority of rivers.

This project consists of developing a methodology for estimating expected floods over the coming decades that will integrate uncertainty related to the use of pseudo-observations in the absence of flow measurements and uncertainty related to the use of climate simulations, hence the title Integrative Frequency Analysis. These flood estimates will be used to draw up new flood maps for Québec.

• Develop a non-stationary frequency analysis method to estimate the level of future floods on gauged rivers (with observations) and non-gauged rivers (with pseudo-observations provided by another INFO-Crue project);

• Implement the developed method on 18,000 reaches provided by the Direction de l’expertise hydrique du Québec (DEH) to estimate flood levels occurring on average once every 100 years, once every 350 years and once every 400 years over the next 50 years;

• Develop a method to approximate water levels in confluence zones.

• Develop a frequency analysis model for pseudo-observations that integrates their uncertainty;

• Develop a non-stationary frequency analysis model for simulated flows from a large set of climate simulations;

• Assemble the two models to integrate the sources of uncertainty;

• Utilize the model to estimate flood levels.

Once completed, the project will have led to the development of a frequency analysis method integrating various sources of uncertainty and non-stationary behaviour, and to the estimation of flood levels occurring on average once every 100 years, once every 350 years and once every 400 years over the next 50 years for the 18,000 reaches studied.

This project was funded by Ouranos as part of the support for the MELCC's INFO-Crue initiative.