North Pacific atmospheric rivers and their influence on western North America at the Last Glacial Maximum

Southwestern North America was wetter than present during the Last Glacial Maximum. The causes of increased water availability have been recently debated, and quantitative precipitation reconstructions have been underutilized in model-data comparisons. We investigate the climatological response of North Pacific atmospheric rivers to the glacial climate using model simulations and paleoclimate reconstructions. Atmospheric moisture transport due to these features shifted toward the southeast relative to modern. Enhanced southwesterly moisture delivery between Hawaii and California increased precipitation in the southwest while decreasing it in the Pacific Northwest, in agreement with reconstructions. Coupled climate models that are best able to reproduce reconstructed precipitation changes simulate decreases in sea level pressure across the eastern North Pacific and show the strongest southeastward shifts of moisture transport relative to a modern climate. Precipitation increases of ∼1 mm d⁻¹, due largely to atmospheric rivers, are of the right magnitude to account for reconstructed pluvial conditions in parts of southwestern North America during the Last Glacial Maximum.