The Holocene precipitation dipole pattern in the Asian drylands: Mechanisms and processes from PMIP4 simulations and paleo-proxy evidence

Asian drylands encompass Arid Central Asia (ACA) and West Asia (WA), where water vapor transport is consistently governed by the westerlies. Recent research has identified a dipole pattern in Holocene hydroclimate changes between the ACA and WA, challenging previous assumptions of uniform hydroclimate shifts across the westerlies-dominated mid-latitudes of the Northern Hemisphere. However, the mechanisms behind the dipole pattern remain largely unknown. Our findings demonstrate that PMIP4 models accurately reproduced the dipole pattern, attributing it mainly to contrasting spring precipitation changes. From the middle to late Holocene, strengthened westerlies led to increased precipitation in the ACA. In contrast, rising spring solar insolation intensified the subtropical high, leading to reduced water vapor and increased descending air movement in WA, which decreased precipitation in the region. Our study suggests that WA is a distinctive region within the westerlies-dominated mid-latitudes, where low-latitude processes led to inconsistent precipitation variations from the middle to late Holocene.