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

极端降水是影响加拿大东部的最具破坏性和最昂贵的天气现象之一。在寒冷的季节，降雪事件会对地面和空中交通造成巨大的干扰。在夏季和平季，极端降雨可能导致洪水，造成广泛的经济和环境破坏。由于各种过程经常相互竞争，预计未来极端降水将发生变化。一方面，由于大气变暖导致大气含水量增加，预计极端降水将增加。另一方面，与对温度分布变化的响应（即斜压性和稳定性）有关的大尺度环流变化预计将导致温带风暴减少和极端降水减少。此外，由于水成物变化而释放的额外潜热和微物理效应等一些精细尺度过程和反馈所起的作用存在很大的不确定性。因此，评估未来极端降水的变化需要考虑几个空间和时间尺度上的复杂过程，而目前的气候模式，无论是全球模式还是标准区域模式，都无法再现这些过程，因为它们的分辨率很低，而且某些过程的参数化有些过于简单。我的“发现”号研究的首要目标是确定未来加拿大东部极端降水事件强度变化的原因。提出的研究计划是根据两个主要问题，结合先进的建模和最先进的观察：1。新开发的允许对流的模式能在多大程度上代表观测到的极端降水？2. 极端降水强度的预估变化是什么？这些变化如何取决于湿度（热力学）和降水类型（微物理学）？这项研究将利用一个非常高分辨率的气候模型，该模型明确模拟对流过程（允许对流），并包括云和降水微物理过程的复杂表示。为了限制所需的计算资源，该模型使用动态降尺度技术在有限的区域内运行，并且在有限数量的先前已确定的强降水事件中运行。对未来气候的模拟将使用未来环境的层次结构，其中以逐步的方式引入不同的变化，以帮助分离未来变化的主要来源。也就是说，破坏性风暴的演变将首次在千米尺度的分辨率上进行探索，利用模拟当前和可能的未来条件的边界强迫。研究结果将支持制定适应战略，以减轻未来极端降水对径流、淡水资源和洪水的影响。

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.