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A2. Freezing rain occurrence and severity changes in future climate

The many types of precipitation that occur in Canada during winter storms may lead to major disruptions to the society by affecting power networks, the aviation industry and ground transportation. Winter precipitation commonly observed in Eastern Canada can be in the form of rain, freezing rain, ice pellets and wet snow. The prediction of the type of winter precipitation is challenging when it is formed at temperatures near freezing, as their formation and evolution imply phase changes that impact the dynamics and thermodynamics of storms.

Despite their importance, cloud and precipitation processes are still rather poorly represented in climate models, in part due to their coarse resolution and high computing cost of complex microphysical formulations. It is proposed to start testing existing microphysics schemes in the Canadian NWP Global Environmental Multiscale (GEM) model, followed later by the implementation of more detailed bulk microphysics scheme predicting six hydrometeor categories. Systematic studies will be carried out to study the performance as a function of the complexity of the microphysics scheme, model domain size, vertical resolution, time step etc. Simulations for selected periods will be conducted with the old and new microphysics scheme and compared with available observations. The integrations will later be extended to future climate to study the changes in the location and timing of various precipitation types, i.e., to study if freezing-rain producing storms could become more/less frequent/severe under future climate. Simulations will also be conducted to study the impact of local topographic forcing such as the SLRV on the occurrence of freezing rain.