Recent Escalation of Winter Fire-Weather Risk in the Southwestern United States: Roles of Anthropogenic Warming and the Negative Pacific Decadal Oscillation.

Abstract

Winter wildfires in the southwestern United States (SWUS), especially Southern California, are less frequent than summer and autumn fires but can be highly destructive, as demonstrated by the January 2025 events. How winter anthropogenic warming and internal climate variability shape winter fire weather risk in the SWUS remains unclear. Using historical observations, reanalysis, and model simulations, we show that winter fire weather risk in the SWUS has nearly doubled during 1984-2024. An attribution analysis associates approximately 33% of this increase with anthropogenic ocean warming and 53% with internal Pacific Decadal Oscillation (PDO) variability. Winter North Pacific midlatitude war..