Event definition

XAIDA defines the event intensity as the temperature anomaly averaged over the region (45–52 ºN, 119–123 ºW) used in Philip et al. (2021) including the cities of Seattle, Portland, and Vancouver (with well over 9 million people in their combined metropolitan areas). Different event durations from 1-day to 5-day temperature anomalies are analyzed.

Objectives

XAIDA aims at improving the understanding of the driving physical mechanisms of this event, at putting the event into a long-term climatological context and at quantifying to what extent human activities have altered the odds of the Pacific Northwest heatwave to occur. Finally, XAIDA addresses the question whether the potential for such a record breaking event could have been foreseen before the event.

In a workshop in early February 2022 co-organized by WP5 and WP6 participants shared their initial results on the above objectives and co-ordinated future tasks in addressing research questions. The workshop helps to coordinate the use of a common event definition for future work. 

WP6 presented a detailed analysis of the processes driving the Pacific Northwest heatwave. The event was driven by an intense anticyclone situated over the heatwave region. A detailed analysis revealed the pathways along which the air masses moved towards the center of the heat anomaly, and quantified the process along these trajectories to the extremely hot air masses that ultimately reached the heatwave region. 

WP5 presented initial analyses demonstrating that in principle the possibility for such an event could have been foreseen based on statistical methods and targeted climate model-based experiments. The statistical analysis of the event is based on a weather generator that resamples extreme states (“empirical importance sampling”), and the climate model experiments are designed to repeatedly simulate a specific extreme event with slightly perturbed initial conditions (“climate model boosting”) to generate different trajectories of this extreme event.

Based on these findings WP5 aims to develop storylines for other record breaking heatwave events unseen in the observational record that have not yet occured. WP5 coordinates the definition of potentially impact-relevant other heatwave events e.g. for the 2024 Summer Olympics in Paris for which heatwave storylines are developed comparing different approaches developed within the XAIDA project.