The Little Ice Age (LIA) was a period of most recent glacial advancement and had pronounced cooling effect in the North Atlantic region. Synchronous hydroclimate changes are also reported from the Himalayas, however owing to the heterogeneity within the proxy reconstructions, their relationship with LIA cooling is unclear. Varied topography, huge glacial mass, and multiple moisture sources (both from the Indian Summer Monsoon (ISM) and the Westerlies) makes understanding of the impact of LIA cooling on this region ambiguous. In this study, we review and assess the existing paleoclimatic proxy records for a comprehensive analysis of the regional response of the Western Himalayas to LIA cooling. Using the existing meteorological reanalysis data for back trajectory analysis for the last 20 years, the Western Himalayan region was classified into three different zones based on the relative percentage of moisture-bearing-wind-source contribution. The upper Western Himalayas receive most of the moisture from the Westerlies, both Middle and Lower Western Himalayas receive majority of rainfall from the ISM, with a relatively higher contribution of Westerlies in the Lower Western Himalayas. Comparison of reconstructions using Principal Component Analysis reveal consistent high moisture conditions during the LIA, with increased winter precipitation and decreased summer precipitation coherently in all the records. Spectral analysis of the available proxy records and various climate forcing for LIA cooling show similar dominant frequency, attesting that the LIA cooling drove the hydroclimate changes in the Western Himalayan region. External forcings such as decreased solar activity and increased volcanic activity caused cooling, influenced the Inter Tropical Convergence Zone, and resulted in weaker summer rainfall during the LIA. Synchronous changes in the North Atlantic Oscillations and El Niño–Southern Oscillation records with precipitation records suggest a link between “monsoon breaks” and enhanced Westerly intensity and an intensified winter precipitation in this region.

中文翻译：

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评估小冰期期间喜马拉雅山西部的水文气候变化

小冰期（LIA）是最近冰川进展的时期，对北大西洋地区有明显的降温作用。喜马拉雅山也报告了同步水文气候变化，但由于代理重建的异质性，它们与 LIA 降温的关系尚不清楚。多样的地形、巨大的冰川和多种水分来源（均来自印度夏季季风 (ISM) 和西风带）使得 LIA 降温对该地区的影响的理解不明确。在这项研究中，我们回顾和评估了现有的古气候代理记录，以全面分析喜马拉雅山脉西部对 LIA 降温的区域响应。利用现有气象再分析数据进行过去20年的回溯轨迹分析，根据含水量风源贡献的相对百分比，将喜马拉雅西部地区划分为三个不同的区域。喜马拉雅山西上部的大部分水汽来自西风带，中喜马拉雅山和西喜马拉雅山下部的大部分降雨来自ISM，其中西喜马拉雅山西下部的西风带贡献相对较高。使用主成分分析进行重建的比较揭示了 LIA 期间一致的高湿度条件，所有记录中冬季降水量增加，夏季降水量减少。对 LIA 变冷的可用代理记录和各种气候强迫的光谱分析显示出相似的主导频率，证明 LIA 变冷驱动了喜马拉雅西部地区的水文气候变化。太阳活动减少和火山活动增加等外部强迫导致气温变冷，影响热带辐合带，并导致 LIA 期间夏季降雨减弱。北大西洋涛动和厄尔尼诺-南方涛动记录与降水记录的同步变化表明，“季风中断”与西风强度增强以及该地区冬季降水加剧之间存在联系。