Uneven Indian monsoon response to the 4.2 ka event

Centennial-scale variability in the Indian summer monsoon (ISM) is critical for understanding past climate dynamics and their societal implications. However, a precise understanding of how the 4.2 ka aridification affects hydroclimate across the Indian monsoon domain remains elusive. Here we present century-scale ISM variability from the Chandratal peat bog in the northwestern Himalaya, which spans the past 7.8 ka. Proxy records indicate a stronger ISM and higher lake levels during the middle Holocene. A pronounced arid phase between ~4.5 and 3.0 thousand years ago (ka) aligns with the 4.2 ka event, although the transition in this region appears gradual. Our results suggest that the 4.2 ka event in the northwestern Himalayas was characterized by multicentury aridification, contributing to a more nuanced understanding of its timing and structure across the Indian subcontinent. The arid phase aligns with an enhanced influence of winter westerlies, underscoring summer-winter hydroclimate coupling during the mid- to late Holocene.