In the context of global warming, increasing frequency of climate extremes poses a great challenge to natural systems and humankind. However, the spatial and temporal characteristics, as well as the mechanisms of extreme climate change, remain insufficiently understood, particularly in arid and semi-arid mountainous regions with high climate sensitivity and ecological fragility. In this study, we analyzed the spatial and temporal characteristics of 27 extreme climate indices (including intensity, duration, and frequency) in the Qilian Mountains, northeastern Tibetan Plateau, from 1961 to 2016 using the CN05.1 meteorological grid dataset, explored the relationship between the extreme climate indices and internal variability of the climate system (e.g., the North Atlantic Multi-decadal Oscillation (AMO), the Pacific Decadal Oscillation (PDO), and the Arctic Oscillation (AO)), and further probed into the mechanisms affecting climate extremes using ERA5 reanalysis dataset. The results showed that extreme temperatures in the Qilian Mountains were significantly enhanced in terms of intensity, frequency, and duration during 1961–2016. The decrease rates of frost days (FD0) and ice days (ID0) were − 4.4 d per decade and − 4.7 d per decade, respectively, and the increase rate of growing season length (GSL) was 2.9 d per decade. Extreme precipitation intensity increased significantly, with the intensity indices R95P and PRCPTOT showing the most significant change trends of 4 mm per decade and 14.9 mm per decade, respectively ( < 0.05). The number of consecutive dry days (CDD) displayed a significant downward trend, with a rate of −6 d per decade, the number of moderate precipitation days (R10) showed an increasing trend of 0.12 d per decade. Correlation analyses revealed significant associations between the increases in extreme climates and the AMO and PDO. Additionally, the enhancement of the AO contributed to the increased extreme precipitation. Enhanced anticyclonic circulation in Eurasia and geopotential height, as well as increased cloud cover in winter, were the main reasons for the increase in extreme temperatures in the Qilian Mountains, whereas the significant increase in water vapor transport entering the east boundary of the Qilian Mountains in summer mainly contributed to the increase in extreme precipitation. This study highlights internal oscillations in the climate system that regulate the extreme climate variability in the Qilian Mountains at various spatial-temporal scales.

中文翻译：

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青藏高原东北部极端气候事件增多及其与大气环流变化的关系

在全球变暖的背景下，极端气候事件的发生频率不断增加，对自然系统和人类提出了巨大的挑战。然而，人们对极端气候变化的时空特征和机制仍知之甚少，特别是在气候敏感性高、生态脆弱的干旱半干旱山区。本研究利用CN05.1气象格网数据集，分析了1961—2016年青藏高原东北部祁连山地区27个极端气候指数（包括强度、持续时间和频率）的时空特征，探讨了二者之间的关系。极端气候指数与气候系统内部变率（如北大西洋数十年涛动（AMO）、太平洋年代际涛动（PDO）、北极涛动（AO））之间的关系，并进一步探讨影响机制使用 ERA5 再分析数据集的极端气候。结果表明，1961—2016年祁连山极端气温在强度、频率和持续时间上均显着增强。霜冻日数（FD0）和结冰日数（ID0）的减少率分别为每十年-4.4天和每十年-4.7天，生长季长度（GSL）的增加率为每十年2.9天。极端降水强度显着增加，强度指数R95P和PRCPTOT变化趋势最为显着，分别为4毫米/10年和14.9毫米/10年（ < 0.05）。连续干旱日数（CDD）呈显着下降趋势，每10年下降-6 d，中等降水日数（R10）呈每10年上升0.12 d趋势。相关分析揭示了极端气候的增加与 AMO 和 PDO 之间存在显着关联。此外，AO的增强也导致了极端降水的增加。欧亚大陆反气旋环流增强、位势高度增强以及冬季云量增加是祁连山极端气温升高的主要原因，而2017年进入祁连山东缘的水汽输送显着增加。夏季是极端降水增加的主要原因。这项研究强调了气候系统的内部振荡，这些振荡在不同的时空尺度上调节着祁连山的极端气候变化。