Decoupled Indian Summer Monsoon Intensity and Effective Moisture Since the Last Glaciation in Southwest China.

Effective moisture (EM) distribution in the Indian summer monsoon (ISM) region is strongly related to regional topography. An understanding of climate change and the interactions between climate variables can help predict future climate variations. Here, we reconstruct a stack EM record for Southwest China over the past 90 kyr using environmental magnetism in lake sediment. The EM in Southwest China at the orbital scale was closely linked to precession‐induced change in North Hemisphere solar insolation, as well as the ISM variability. However, at the glacial‐interglacial scale, it was decoupled with ISM intensity, being wetter during glacial periods (weakened ISM) and drier during interglacial periods (enhanced ISM). Combined with modern meteorological observations, we suggest that the topographical barrier effect and temperature induced dryness are responsible for the decoupling between ISM intensity and EM. The terrestrial topography and temperature strongly influence EM distribution by altering the dynamics of onshore airflow and evapotranspiration. Plain Language Summary: Effective moisture (EM) directly affects hydrological cycle and wider‐scale socio‐economic development. Reconstruction of prehistoric EM levels is essential for deeper understanding of the global climate system, developing climate models and improving prediction of future climate variations. Here, we reconstruct a high‐resolution EM record over the past ∼90,000 years from lake sediments in Tengchong, Yunnan province, Southwest China. We found that the variation of precession (shifts in the rotational axis of the Earth) and solar insolation are the key contributors to the EM variability at the orbital scale. Unusually, a wetter climate during the glacial period and relatively drier interglacial periods were observed in our records, which is opposite to those found in previous studies (arid glacial and humid interglacial) in monsoon regions, indicating a decoupling pattern between monsoon intensity and EM in study region. Based on a comprehensive analysis of the modern meteorological observations, we conclude that the topography and temperature exert a considerable role in modulating EM distribution and response to the decoupling pattern. Key Points: The long‐term effective moisture (EM) record in Southwest China since ∼90 kyr was reconstructedThe EM variability at the orbital scale in terrestrial Indian summer monsoon region is primarily dominated by precessionThe topographic barrier and temperature induced aridification contribute to the decoupling of monsoon intensity and EM [ABSTRACT FROM AUTHOR]