Abstract Recent observations indicate that over the last decades, climate change has increasingly influenced the frequency, intensity and duration of extreme climatic and hydrologic events. The main aim of this study is to determine the hydrologic response, especially the flood evolution, of the Lena River in Eastern Siberia to ongoing climate change. Draining the coldest region of the Northern Hemisphere, the Lena River is impacted by global warming, which is particularly pronounced in periglacial areas characterized by deep and continuous permafrost. We document the hydrologic variability of the Middle Lena River, first by characterizing trend and stationarity of monthly discharges. Second, we analyze on the basis of the peak over threshold method (POT) the temporal evolution of intensity and duration of three discharge classes: bar-full discharge, bank-full discharge and large floods. Finally, we also determined the dates of the flood beginning and of the flood peak. Data on mean monthly discharge and flood peaks are available since 1936 and daily discharges since 1954. Our results provide evidence for a net hydrologic change with an increase in the intensity and duration of floods in the two decades ending in 2012. The frequency of high floods is unprecedented, and small floods no longer occur. The tail of the temporal distribution of the flood peak is also changing. More frequent early floods are occurring in spring with secondary flood peaks in summer, the latest probably represents the most striking change. Furthermore, the changes have been accelerating since 2004. Finally, two islands were instrumented (2008–2012) in order to study the flooding dynamics with a better precision.

中文翻译：

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顺其自然：勒拿河中游（西伯利亚）对气候变率和变化的水文响应

摘要 最近的观察表明，在过去的几十年里，气候变化对极端气候和水文事件的频率、强度和持续时间的影响越来越大。本研究的主要目的是确定东西伯利亚的勒拿河对持续气候变化的水文响应，尤其是洪水演变。勒拿河是北半球最寒冷的地区，受全球变暖的影响，这在以深而连续的永久冻土为特征的冰缘地区尤为明显。我们首先通过表征月流量的趋势和平稳性来记录勒拿河中游的水文变化。其次，我们基于峰值超阈值法（POT）分析了三种排放等级的强度和持续时间的时间演变：全坝泄洪、全岸泄洪和大洪水。最后，我们还确定了洪水开始和洪水高峰的日期。1936 年以来的月平均流量和洪水峰值数据以及 1954 年以来的日流量数据都可用。我们的结果提供了证据，表明在 2012 年结束的 20 年里随着洪水强度和持续时间的增加，净水文变化会发生。 高洪水的频率史无前例，小洪水不再发生。洪峰时间分布的尾部也在发生变化。春季更频繁地发生早期洪水，夏季出现次生洪水，最晚可能代表了最显着的变化。此外，自 2004 年以来，变化一直在加速。 最后，