Modélisation et analyse de l'impact du changement climatique sur les inondations de la rivière du Richelieu mises en contexte avec la crue extrême du printemps 2011

Abstract

The Richelieu River takes its source from Lake Champlain and flows in a northwardly direction all the way to the Saint-Lawrence River. The Richelieu River watershed is encompassed by the states of New York and Vermont in its US portion, and by the province of Quebec in Canada. Lake Champlain is a natural reservoir located at the center of the watershed. With its large storage volume, Lake Champlain damps all incoming floods, thus protecting the Richelieu River. In 2011, Lake Champlain reached a record-shattering level, which resulted in extreme flows in the Richelieu River. Major flooding ensued and hundreds of houses had to be evacuated for up to 2 months. Direct economic losses were estimated at 70 M$. The 2011 event reignited the flood mitigation debate on the Richelieu River and pointed to the necessity of evaluating the potential contribution of climate change to flooding trends, and establishing adaptation strategies. The objectives of this work are to evaluate future flows tendencies on the Richelieu River and Lake Champlain, to better understand the nature of the 2011 flood. Future tendencies were evaluated by setting up a computer model of the Richelieu River watershed and by using climate model simulations downscaled using two different methods. Results show a decreasing tendency of extreme spring floods for every considered return period. This trend is reversed for fall-winter extreme floods where an increasing trend is predicted. In addition, an analysis of the 2011 spring flood was conducted based on the comparison with three other large floods which happened in 1993, 1998 and 2008. The 2011 flood was triggered by extreme rainfall during the months of April and May (500-year return period), combined with a 15-year snowpack on most of the watershed. These elements combined and resulted in a 700+-year return period for both maximum lake level and river discharge. Using the 2008 record snow cover, and combining the 2011 spring precipitation, a hypothetical spring flood even larger than the 2011 event was modeled. This hypothetical event increased flows in the Richelieu River by 11% over the 2011 maximum discharge. In conclusion, this work showed that climate change impacts should result in a decreasing tendency for extreme spring flooding. However, natural variability will remain and the risk of very large flood will persist, despite this decreasing tendency. Adaptation measures such as better management of the floodplain should be considered for this watershed.

Date	29 May 2014
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	François Brissette (Supervisor)