Identifying Common Precursors of Decadal Vapor Pressure Deficit Variability in the Southwestern United States

Abstract Atmospheric vapor pressure deficit (VPD) is a useful proxy for meteorological fire-prone conditions in the southwestern United States (SWUS). Here, we demonstrate that the leading VPD mode, with a pronounced decadal component, displays a center of action in the SWUS. In its dry phase, this mode is characterized by reduced soil moisture, high pressure systems, and La Niña–like conditions and connected to decadal sea surface temperature (SST) variability in the Pacific and Atlantic basins. Leveraging climate simulations, a backward model-analog technique reveals persistent SST signals a few seasons preceding the dry VPD mode. While state-of-the-art models can reasonably capture the spatial patterns of VPD, challenges emerge in representing the decadal component of the leading VPD mode, which predominantly arises from misrepresentations of the actual rather than saturation vapor pressure.