Department Seminar: Cheng-Ta Chen

Title: Observed and Projected Changes in Extreme Heatwave Events and Their Attributes in North America

Abstract: Public perceptions of the risk posed by natural hazards and climate change are typically associated with extreme events. There were studies focused on the detailed synergy of processes that lead to the event's occurrence. Past literature on long-term variations of global weather and climate extremes often studies the derived extreme indices and applies further statistical extreme value analysis to data sampled from a station, fixed grid point, or specifically defined area. Our study proposes an alternative framework to track and analyze extremes from an event perspective, including their attributes (e.g., frequency, intensity, duration, areal extent, and total accumulated severity). It should facilitate better communication with the general public on the climate risk, provide more complete different attributes of the extreme events, and do not need to be limited to a pre-defined location or domain.

Heatwaves account for more fatalities than floods, tornadoes, hurricanes, and lightning combined in the USA. Using long-term ERA5 temperature analysis data from 1940, we investigate how the different attributes of the most intensive heatwave events change over time in North American regions. We first identify all extreme heatwave events with an event tracking algorithm using daily heatwave intensity with a selected intensity threshold for heatwave occurrence and the size of spatiotemporal connected heatwave occurrence. After archiving all the extreme heatwave events, it is possible to rank all the historical events by total integrated severity of heatwave events in North America and subregions. The long-term trends and variations of all different attributes of extreme heatwave events can also be studied. With the information on the spatial and temporal evolution of extreme events, it's also possible to further study the associated weather system and environmental conditions that fueled the heatwave extremes or assess potential impact with exposure and vulnerability information. Similarly, using daily temperature from CMIP6 models, we will discuss the ability of climate models to reproduce the characteristics of observed heatwave events and how the projected record-breaking extreme heatwave events will change in the future.