Indian Ocean Dipole extremes extend seasonal predictability of North China Plain summer heat

Seasonal predictability of regional extreme heat depends on how boundary-condition signals shape intrinsic error growth. Here we examine whether May–July (MJJ) Indian Ocean Dipole (IOD) extremes modulate the predictability limit (PL) of summer extreme maximum temperature (TXx) over the North China Plain (NCP). Using ERA5-derived TXx and a nonlinear local Lyapunov exponent framework, we show that both negative and positive IOD extremes slow early TXx error growth relative to neutral IOD conditions. The NCP TXx PL increases from 2.78 months in neutral years to 4.14 months for combined IOD extremes. Composite diagnostics link this extension to organized Indo-Pacific convection, western North Pacific circulation, and local moisture–cloud–radiation constraints. TXx amplitude is not enhanced, indicating that longer predictability arises from constrained local evolution rather than stronger heat anomalies. These results identify MJJ IOD extremes as a boundary-condition context for enhanced seasonal TXx potential predictability.