Synoptic and mesoscale processes associated with meteorological extremes at Vancouver, British Columbia in the current and future climate
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Date
2019
Authors
Betancourt, Daniel
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Abstract
The synoptic and mesoscale processes generating hazards in the climate of Vancouver, British Columbia are examined in this thesis. Those considered have been shown through quantitative methods to pose risk to local populations. These include heatwaves, landslides and windthrow of trees (the latter 2 are associated with antecedent heavy rain).
Landslide events are associated with moisture transport from lower latitudes, but extreme wind events preceded by heavy rain do not show such linkage. Patterns associated with extreme winds vary depending on antecedent heavy precipitation - with differences in pressure anomalies over the North Pacific versus British Columbia. Increases in landslide events are related to northwards shifting moisture sources in the Pacific, while decreases in positive pressure anomalies over this region explain decreases in purely wind events. Multiday heatwaves represent a unique process associated with upper blocking and surface West Coast Thermal Trough (WCTT) configurations. Greater occurrences in the former are increasing the intensity and duration of heatwaves. Other patterns show temporal sensitivity in prominence during multiday events.
Temporal processes regulating mesoscale circulations account for 36-38% of spatial variability in attaining heat-alert criteria between Vancouver (YVR) and Abbotsford (YXX) International airports. Considerable dynamic forcing occurs - whereas heatwaves elsewhere are typically associated with barotropic conditions. The WCTT and coastal southerlies modulate differentially the occurrence of sea-breezes at YVR and YXX.
Verification of model data for a July 2009 heatwave event suggests that magnitude and error in u-component flow are associated with v-wind intensity; and coastal southerlies are
shown to deflect and produce offshore flows at YVR. Modulation of sea-breezes occurs due to dynamic forcing rather than thermodynamic parameters such as sensible heat flux, whereas mountain-valley circulations are sensitive to Planetary Boundary Level Height. Data from a future simulation using a Pseudo-Global Warming (PGW) approach show large increases in temperature and humidex at YVR and YXX causing considerably more heat stress. Intensification of winds occurred in the future simulation driven by a stronger WCTT. Climate perturbations in geopotential height and u and v wind applied to the model in the PGW simulation did not appear to have affected changes in the WCTT.
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Keywords
Extremes, Meteorology, Vancouver