Abstract
The west coast of Canada is strongly affected by the extreme precipitation events triggered by frequent atmospheric river (AR) activities over the eastern North Pacific. Across the region, assessing the probable maximum precipitation (PMP), can provide valuable information for resilience building of the coastal communities that are vulnerable to hydrological risks. In this study, a 3-km convection-permitting regional climate model is used to physically estimate the PMP in Vancouver. This technique maximizes the effect of AR-related water vapor transport by spatially adjusting the lateral boundary conditions (LBCs) of the model simulations for the selected AR-related extreme precipitation events. The PMP in Vancouver is identified among the simulations driven by the spatially adjusted LBCs that are corresponding with the AR-induced “worst-case scenario,” i.e., landfalling ARs hit Vancouver with optimal landfalling location and transport direction. Results suggest that the PMP in Vancouver, in terms of the maxima of the regionally averaged 72-h total precipitation for the historical extreme precipitation events, is up to 790 mm, which is 130% greater than the historical peak precipitation for the period 1980∼2017. On average, all the PMP simulations shows an overall increase by 81% in precipitation by relative to historical simulations. In addition, the PMP simulations suggested an overall decrease in snowfall by 12% due to the warmer near-surface air temperature; however, a pronounced increase in freezing rain is seen. The precipitation increase for the estimated PMP relative to the historical extreme precipitation is closely associated with the increased atmospheric moisture transport and the changes in the atmospheric dynamic factors when the AR effects are maximized. These include the enhanced low-tropospheric ascent and moisture transport convergence, which can induce stronger depletion of atmospheric moistures as indicated by the increased precipitation efficiency.
Highlights
Extreme precipitation events can result in great economic losses in North America (Changnon and Hewings, 2001; Kunkel et al, 2013; Dottori et al, 2018; Davenport et al, 2021)
Based estimations of PMP are performed for the Metro Vancouver region and the PMP-associated environmental mechanisms are analyzed based on the GEMCLIM simulations driven by spatially adjusted LBCs
Through maximization of the influence of atmospheric rivers (ARs), PMP simulations for the historical extreme precipitation events show an increase in the 72-h regional average of precipitation over Metro Vancouver by 81% on average compared with the historical simulations of the events
Summary
Extreme precipitation events can result in great economic losses in North America (Changnon and Hewings, 2001; Kunkel et al, 2013; Dottori et al, 2018; Davenport et al, 2021). Using limited area numerical weather model simulations, the study of Ohara et al (2011) attempted to simulate precipitation with physically adjusted lateral boundary conditions (LBCs) in order to estimate PMP over a targeted watershed. One of the approaches to adjust LBCs is to ideally maximize the relative humidity value to 100% in the LBCs for selected severe storm events (Ishida et al, 2015a) Using this method, Ishida et al (2015a) found that the estimated PMP indicate up to 74% increase of precipitation relative to the historical peak precipitation for the case of Northern California. A highresolution regional climate model based on the 4.8.12 version of Environment Canada’s Global Environment Multiscale in CLImate Model (GEMCLIM) is used to simulate the PMP values for the AR-related extreme precipitation events in Metro Vancouver. We calculate the large-scale precipitation efficiency, defined by the ratio of total precipitation to IWV during a certain period of time, to indicate how effective are the atmospheric dynamical processes in converting the available total column moisture to precipitation (Tuller, 1973; Ye et al, 2014)
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