Future intensity of precipitation extremes over eastern Canada using very high-resolution modelling

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Precipitation extremes are among the most damaging and costly weather phenomena to impact eastern Canada. During the cold season, snowfall events can produce massive disruptions in ground and air transportation. In summer and shoulder seasons, rainfall extremes can lead to flooding causing extensive economic and environmental damage. Precipitation extremes are expected to change in the future due to various processes often competing with each other. On the one hand, precipitation extremes are expected to increase due to the increase in atmospheric moisture content in response to the warming of the atmosphere. On the other hand, large-scale circulation changes associated with responses to changes in temperature distributions (i.e., baroclinicity and stability) are expected to lead to less extratropical storms and decreases in precipitation extremes. In addition, there are large uncertainties about the role to be played by some fine-scale processes and feedbacks including the extra latent heat being released and microphysical effects due to changes in hydrometeors. Assessing future changes in extreme precipitation thus requires considering several complex processes at spatial and temporal scales that current climate models, either global or standard regional models, are unable to reproduce due to their coarse resolution and somewhat simplistic parameterization of some processes. The overarching aim of my Discovery research is to determine the causes of future changes in the intensity of extreme precipitation events over eastern Canada. The proposed research program is structured according to two primary questions that combine advanced modelling with state-of-the-art observations: 1. How well do the newly developed convection-permitting models represents observed precipitation extremes? 2. What are the projected changes in the intensity of extreme precipitation and how these changes depend on the amount of moisture (thermodynamics) and the type of precipitation (microphysics)? This research will make use of a very high-resolution climate model that explicitly simulates convective processes (convection permitting) and includes a sophisticated representation of cloud and precipitation microphysical processes. To limit the required computational resources, the model is run over a limited area using the dynamical downscaling technique, and for a limited number of events where heavy precipitation has been previously identified. Simulations of future climate will use a hierarchy of future environments where different changes are introduced in a stepwise manner to help isolate key sources of future changes. That is, for the first time, the evolution of damaging storms will be explored at kilometre-scale resolutions using boundary forcings that emulate present and plausible future conditions. Outcomes will support the development of adaptation strategies to mitigate the future impact of extreme precipitation on runoff, freshwater resources and flooding.