Warming since the Last Glacial Maximum amplifies Northern Hemisphere drought expansion driven by the Pacific Decadal Oscillation

The Pacific Decadal Oscillation (PDO) modulates decadal precipitation patterns, and subtropical troughs act as rainfall “commanders”. However, whether PDO influences precipitation variability by affecting these troughs remains unclear. By combining reanalysis data with present-day and Last Glacial Maximum (LGM) simulations, we reveal that PDO regime shifts regulate spring precipitation by altering subtropical trough positions and associated wind patterns. A negative PDO phase deepens the India-Burma trough and shifts its base ~1330 km equatorward, inducing northeasterly anomalies to its east that weaken moisture transport and suppress precipitation over East Asia. Concurrently, it shallows the North American subtropical trough and shifts its base ~560 km poleward, promoting a ridge development that reduces precipitation in water-stressed western North America. Notably, the 4-6 °C warming since the LGM has amplified the negative PDO drying effect, increasing affected area by 160% in East Asia and 57% in North America. These results clarify how the PDO regulates subtropical trough dynamics to shape spring precipitation, providing a mechanistic basis for drought risk assessments under similar warming magnitude to that projected for this century. The Pacific Decadal Oscillation regime shifts modulate the spring precipitation patterns across East Asia and western North America by altering subtropical trough positions, and the drying effect associated with its negative phase is amplified by warming since the Last Glacial Maximum, as revealed by reanalysis and model experiments.