Les impacts du changement climatique sur le volume des crues dans les bassins versants d'Amérique du Nord

Abstract

With the effects of anthropogenically induced climate change, extreme events such as droughts and floods have been projected to increase in terms of frequency, intensity and magnitude for the majority of the North American continent. Whether it be for hydroelectric purposes or water retention services to provide potable water in times of droughts or protection in times of floods, assessing the effects of future climate change on flood volumes is crucial to provide better management of such disasters given the severity of the devastating impacts of flooding. Further, using flood volume instead of flood peak is critical because the latter focuses on the highest possible discharge observed during a flood event, while flood volume also considers flow duration, which is an important factor in terms of the damage caused to the built environment. This study aims to evaluate the overall impact of climate change on flood volumes over a large sample of 1,403 North American catchments by using a multi-model approach. 2,112 combinations of flood volume projections are established per catchment, resulting of multiple hydrological models fed by multiple bias-corrected climate projections under the RCP4.5 and RCP8.5 climate change scenarios. The second aim of this study is to evaluate the contribution of each uncertainty source of the ensemble approach (hydrological models versus biascorrection methods versus climate models) on the future projected hydrological regimes. The selected ensemble members consist of a 21-member ensemble that includes four lumped hydrological models of varying complexity (GR4J, HMETS, HSAMI and MOHYSE), eleven global climate models (GCMs), four bias correction methods (DBC, MBCn, QDM and TSQM) and two greenhouse gas emission scenarios (RCP4.5 and RCP8.5) that provide the study with a very wide range of results for the reference period, 1971 to 2000, and the future period, 2070 to 2099. The results show that flood volumes are expected to decrease in the western mountainous areas, the Great Lakes region, and the Maritimes, while an increase in flood volumes is likely to occur mainly in eastern North America. We show that the largest projected increases in flood volume under climate change are induced by rain-on-snow snowmelt events. We also demonstrate that hydrological models contribute the most to individual catchment uncertainty and GCMs the second most, while average contribution is lead by GCMs with hydrological models in second. The contribution of GCMs is the second largest in areas of increasing flood volume, i.e., on the west and east coasts of the United States. The results demonstrate that of the 1,403 watersheds included in the study across the continent, approximately 80% of the watersheds will see an increase in flood volumes under the different flood scenarios and thresholds within the 30-year window; with the remaining 20% seeing a decrease in flood volumes. This will allow policymakers to make better decisions for flood prevention and mitigation of damage.

Date	24 Mar 2023
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Richard Arsenault (Supervisor)