Assessing the impact of climate change on the frequency of floods in the Red River basin

The impact of climate change on the frequency distribution of spring floods in the Red River basin is investigated. Several major floods in the last couple of decades have caused major damages and inconvenience to people living in the Red River flood plain south of Winnipeg, and have raised the question of whether climate change is at least partly responsible for what appears to be more frequent occurrences of high spring runoff. To investigate whether this is the case, a regression model is used to associate spring peak flow at the US-Canada border with predictor variables that include antecedent precipitation in the previous fall (used as a proxy for soil moisture at freeze-up), winter snow accumulation and spring precipitation. Data from the Coupled Model Intercomparison Project - Phase 5 (CMIP5) are used to derive information about possible changes to the predictor variables in the future, and this information is then used to derive flood distributions for future climate conditions. While mean monthly precipitation during the winter months is expected to increase, winters are expected to be shorter in warmer climates and evaporation losses are expected to be higher, resulting in a net reduction in average snow pack accumulations. On the other hand, precipitation during the active snowmelt period is expected to increase. The average of future flood distributions obtained from an ensemble of 16 climate models is close to the distribution fitted to observed data, but there is considerable uncertainty surrounding the average, highlighting the difficulty in assessing changes in the frequency of extreme events.