In the north-eastern Qinghai-Tibet Plateau (QTP), the source area of the Yellow River (SAYR) has been experiencing significant changes in climatic and environmental conditions in recent decades. To date, few studies have combined modern hydrological conditions with paleoclimate records to explore the mechanism(s) of these changes. This study seeks to improve understanding of hydrological variability on decadal and centennial timescales in the SAYR and to identify its general cause. We first determined annual fluctuations in the surface area of Lake Ngoring from 1985 to 2020 using multi-temporal Landsat images. The results show that lake surface area changes were generally consistent with variations in precipitation, streamflow and the regional dry-wet index in the SAYR, suggesting that the water balance of the Lake Ngoring area is closely associated with regional hydroclimate changes. These records are also comparable to the stalagmite δ¹⁸O monsoon record, as well fluctuations in the Southern Oscillation Index (SOI). Moreover, an association of high TSI (total solar insolation) anomalies and sunspot numbers with the expansion of Lake Ngoring surface area is observed, implying that solar activity is the key driving factor for hydrologic variability in the SAYR on a decadal timescale. Following this line of reasoning, we compared the δ¹³C_org-based lake level fluctuations of Lake Ngoring for the last millennium, as previously reported, with the hydroclimatic history and the reconstructed TSI record. We conclude that the hydrological regime of Lake Ngoring has been mainly controlled by centennial fluctuations in precipitation for the last millennium, which is also dominated by solar activity. In general, it appears that solar activity has exerted a dominant influence on the hydrological regime of the SAYR on both decadal and centennial timescales, which is clearly manifested in the variations of lake area and water level of Lake Ngoring.

在青藏高原东北部，黄河源区近几十年来气候和环境条件发生了显着变化。迄今为止，很少有研究将现代水文条件与古气候记录相结合来探索这些变化的机制。本研究旨在提高对南亚地区十年和百年时间尺度水文变化的认识，并确定其一般原因。我们首先使用多时相 Landsat 图像确定了 1985 年至 2020 年恩戈林湖表面积的年度波动。结果表明，湖泊面积的变化与南亚江流域降水量、径流量和区域干湿指数的变化总体一致，表明恩戈林湖区的水平衡与区域水文气候变化密切相关。这些记录也可与石笋δ ¹⁸ O季风记录以及南方涛动指数（SOI）的波动相比较。此外，观察到高TSI（总日照）异常和太阳黑子数量与恩戈林湖表面积扩大之间的关联，这意味着太阳活动是十年时间尺度上SAYR水文变化的关键驱动因素。按照这一推理，我们将过去千年中恩戈林湖基于δ ¹³ C _{org的湖水位波动（如先前报道）与水文气候历史和重建的 TSI 记录进行了比较。}我们得出的结论是，恩戈林湖的水文状况主要受近千年降水量的百年波动控制，这也受太阳活动的主导。总体而言，太阳活动在十年和百年时间尺度上对南亚江流域水文情势产生了主导性影响，这在恩戈林湖面积和水位的变化上得到了明显的体现。