Human activities have substantially altered present-day flow regimes. The Headwater Area of the Yellow River (HAYR, above Huanghe’yan Hydrological Station, with a catchment area of 21,000 km² and an areal extent of alpine permafrost at ~86%) on the northeastern Qinghai-Tibet Plateau, Southwest China has been undergoing extensive changes in streamflow regimes and groundwater dynamics, permafrost degradation, and ecological deterioration under a warming climate. In general, hydrological gauges provide reliable flow records over many decades and these data are extremely valuable for assessment of changing rates and trends of streamflow. In 1998–2003, the damming of the Yellow River by the First Hydropower Station of the HAYR complicated the examination of the relations between hydroclimatic variables and streamflow dynamics. In this study, the monthly streamflow rate of the Yellow River at Huanghe’yan is reconstructed for the period of 1955–2019 using the double mass curve method, and then the streamflow at Huagnhe’yan is forecasted for the next 20 years (2020–2040) using the Elman neural network time-series method. The dam construction (1998–2000) has caused a reduction of annual streamflow by 53.5–68.4%, and a more substantial reduction of 71.8–94.4% in the drier years (2003–2005), in the HAYR. The recent removal of the First Hydropower Station of the HAYR dam (September 2018) has boosted annual streamflow by 123–210% (2018–2019). Post-correction trends of annual maximum (Q_Max) and minimum (Q_Min) streamflow rates and the ratio of the Q_Max/Q_Min of the Yellow River in the HAYR (0.18 and 0.03 m³·s⁻¹·yr⁻¹ and −0.04 yr⁻¹, respectively), in comparison with those of precorrection values (−0.11 and −0.004 m³·s⁻¹·yr⁻¹ and 0.001 yr⁻¹, respectively), have more truthfully revealed a relatively large hydrological impact of degrading permafrost. Based on the Elman neural network model predictions, over the next 20 years, the increasing trend of flow in the HAYR would generally accelerate at a rate of 0.42 m³·s⁻¹·yr⁻¹. Rising rates of spring (0.57 m³·s⁻¹·yr⁻¹) and autumn (0.18 m³·s⁻¹·yr⁻¹) discharge would see the benefits from an earlier snow-melt season and delayed arrival of winter conditions. This suggests a longer growing season, which indicates ameliorating phonology, soil nutrient availability, and hydrothermal environments for vegetation in the HAYR. These trends for hydrological and ecological changes in the HAYR may potentially improve ecological safety and water supplies security in the HAYR and downstream Yellow River basins.

中文翻译：

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1955-2040年青藏高原黄河源区水流变化及其意义

人类活动已大大改变了当今的流动制度。黄河源区（黄河岩水文站上方的HAYR），集水面积21,000 km ²青藏高原东北部的高山多年冻土面积约为86％），在气候变暖的情况下，河流流态和地下水动力学，多年冻土退化和生态退化一直在发生着广泛的变化。通常，水文仪表可以提供数十年的可靠流量记录，这些数据对于评估流量变化趋势和趋势非常有价值。1998年至2003年，HAYR的第一座水电站对黄河进行了筑坝，这使得对水文气候变量与水流动力学之间关系的研究变得更加复杂。在这项研究中，使用双重质量曲线法重建了1955-2019年黄河沿岸黄河的月流量，然后使用Elman神经网络时间序列方法，对未来20年（2020-2040年）的Huagnhe'yan流量进行预测。大坝的建设（1998–2000年）使HAYR的年流量减少了53.5–68.4％，而在较干燥的年份（2003–2005年）则减少了71.8–94.4％。HAYR大坝第一水电站的近期拆除（2018年9月）使年流量增加了123–210％（2018–2019）。修正后的年度最大值趋势（Q HAYR大坝第一水电站的近期拆除（2018年9月）使年流量增加了123–210％（2018–2019）。修正后的年度最大值趋势（Q HAYR大坝第一水电站的近期拆除（2018年9月）使年流量增加了123–210％（2018–2019）。修正后的年度最大值趋势（Q_最大值）和最小（Q_最小值）水流率和Q的比率_最大/ Q_闵黄河在HAYR（0.18和0.03米³ ·^秒-1 ·年^-1和-0.04年^-1，分别地）与预校正值（分别为-0.11和-0.004 m ³ ·s ^-1 ·yr ^-1和0.001 yr ^-1）相比，更真实地揭示了多年冻土退化的较大水文影响。根据Elman神经网络模型的预测，在未来20年中，HAYR中流量的增长趋势通常会以0.42 m ³的速度加速·s ^-1 ·yr ^-1。春季（0.57 m ³ ·s ^-1 ·yr ^-1）和秋季（0.18 m ³ ·s ^-1 ·yr ^-1）排放速率的上升将受益于较早的融雪季节和冬季推迟到达。这表明生长季节更长，这表明HAYR中的语音学，土壤养分利用率和植被的水热环境有所改善。HAYR中水文和生态变化的这些趋势可能会改善HAYR和黄河下游流域的生态安全和供水安全。