How Do Climate Model Resolution and Atmospheric Moisture Affect the Simulation of Unprecedented Extreme Events Like the 2021 Western North American Heat Wave?

• Published in: Geophysical research letters 2024-07, Vol.51 (14), p.n/a
• Main Authors: Liu, Xue, Saravanan, Ramalingam, Fu, Dan, Chang, Ping, Patricola, Christina M., O’Brien, Travis A.
• Format: Article
• Language: English
• Subjects: Atmospheric moisture; Climate change; Climate models; Climate prediction; Forecasting models; Global climate; Global climate models; Heat; Heat waves; High temperature; Lead time; Moisture; Simulation; Surface temperature; Weather forecasting
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2024GL108160

Although the 2021 Western North America (WNA) heat wave was predicted by weather forecast models, questions remain about whether such strong events can be simulated by global climate models (GCMs) at different model resolutions. Here, we analyze sets of GCM simulations including historical and future periods to check for the occurrence of similar events. High‐ and low‐resolution simulations both encounter challenges in reproducing events as extreme as the observed one, particularly under the present climate. Relatively stronger amplitudes are observed during the future periods. Furthermore, high‐ and low‐resolution short initialized GCM simulations are both able to reasonably predict such strong events and their associated high‐pressure ridge over the WNA with a 1 week forecast lead time. Moisture sensitivity experiments further indicate a drier atmospheric moisture condition results in substantially higher near‐surface temperatures in the simulated heat events. Plain Language Summary During June 2021, an extraordinarily strong heat wave occurred over parts of Western North America (WNA). It obliterated the high temperature record there and caused severe societal and ecological impacts, and is believed to be exacerbated by climate change. Low‐resolution Global Climate Models (GCMs) are currently used to quantify the atmospheric responses to climate change, even though they exhibit significant biases in their simulated climate. Their ability to predict extraordinarily strong heat wave events remains unassessed. In this study, low‐ and high‐resolution GCM simulations are shown to be able to reproduce extraordinarily strong heat wave events in the near future, but face challenges in reproducing the events as extreme as the observed one. This highlights the role of climate change in such events. A suite of short GCM simulations initialized from observations is used to show that even low‐resolution GCMs can forecast observed extreme strong heat wave events and their high‐pressure ridge over WNA at short lead times. We further show that in these short‐term forecasts, drier atmospheric moisture initial condition can lead to significantly higher near‐surface temperature. Key Points Global climate models (GCMs) climate simulations can reproduce extreme heat events, but face challenges in capturing the observed extremity Low‐ and high‐resolution GCMs predict the 2021 Western North America heat wave similarly within a 1‐week forecast lead time Dry atmospheric conditi