Dr. Kit Szeto
Environment and Climate Change Canada
Research areas
Large-scale atmospheric circulation features are important because they link slowly-varying climate drivers such as sea surface temperatures, snowcover or greenhouse gas forcings to the hydroclimate of continental regions. An enhanced understanding of these circulations and the roles they play in governing regional hydroclimate variability and extremes is critical for improving the modeling and prediction of climate change and its impacts. Our CCRN research is focused on identifying and characterizing the dominant circulation features that exhibit the strongest statistical relationships with the hydroclimate of western Canada, the roles they played in affecting past hydroclimate extremes, how well these features are represented in current climate models and the potential roles these features might play in affecting Canada's water future under climate change.
It was found that the three most important circulation patterns that affect the hydroclimate of western Canada are related to slow climate oscillations over the Pacific, Atlantic and Arctic regions, respectively. These circulation patterns are associated with almost stationary large-scale upper atmospheric waves that emanate from the respective remote source regions, and with a major wave ridge or trough that sits over northwestern US/southern BC. These circulation patterns affect the storm activities over western Canada that were critical in the developments of droughts and pluvial in the area. For example, analysis suggests that the increased frequency of major flooding events over the southeast Prairies during the last two decades are likely related to the intensification of the circulation pattern induced by the recent warming (cooling) sea surface temperatures over the western (central) equatorial Pacific. The extreme multi-year drought that affected the Prairies from 1999-2004 was found to be associated with the circulation pattern related to large-scale climate oscillations over the Arctic. On the other hand, the persistent coastal upper ridge that caused the extreme drought over western Canada during 2015 was not associated with any of the identified dominant circulation patterns and we found no evidence that climate change has increased the likelihood for the occurrence of such rare persistent coastal circulation features.
Although most current climate models were able to reproduce the major wave patterns that are associated with the hydroclimate of western Canada, only half of the examined models were able to accurately reproduce the positions and geometry of the waves. Due to the mountainous terrains in western Canada, the regional hydroclimate impacts depend critically on the locations and geometry of the major wave patterns.
Climate model projections suggest that the occurrence likelihoods of strong and persistent upper-level troughs (ridges) over northwestern US could be enhanced during spring (summer) under climate change. Consistent with what we have learned about the hydroclimate impacts of these upper features, more wet spring and dry summer were projected to occur as a result, suggesting that the likelihoods of more severe spring floods and summer drought could be expected over western Canada in a warmed climate. These inferences are supported by analysis of sophisticated drought indicators that were calculated from projected climate conditions in Canada under various greenhouse gas emission scenarios.