Delayed seasonal march of East Asian summer monsoonal rain belt during Heinrich Stadials

Abstract The timing and duration of monsoon rainfall shape regional hydroclimate, yet their response to abrupt climate change remains poorly constrained. Here, we use 25-km-resolution climate simulations to investigate the seasonal migration of the East Asian summer monsoon rain belt during Heinrich Stadials, periods associated with collapsed Atlantic meridional overturning circulation (AMOC). We find that the rain belt migrated northward 18 days later than during interstadials. This delay kept the monsoon front longer over central China, prolonging early-summer rainfall despite an overall weaker monsoon. The delayed migration was linked to later northward advances of the western North Pacific subtropical high and upper-level westerly jet. North Atlantic cooling contributed to these circulation changes through Rossby wave propagation and a weakened land–sea thermal contrast. Our results suggest that abrupt Atlantic changes can reshape both the amount and seasonal timing of East Asian summer rainfall. These findings offer a palaeoclimate perspective on potential changes in monsoon seasonality under future AMOC weakening.