The lakes on the Qinghai-Tibetan Plateau have undergone substantial changes. As intensive cryospheric components change, the response of the lake dynamics to climatic factors, glacier-snow melting, and permafrost thawing has been complex. Based on Landsat images, meteorological data, and glacier and permafrost data, the spatial-temporal changes in the lake area on the northeastern Tibetan Plateau between 1988 and 2019 were analyzed and the driving factors behind the lake changes were further explored. The results suggest that the regional lake area increased from 1988 to 2019 at rates of 0.01-16.03 km(2)/yr. It decreased during 1988-2000, quickly increased during 2000-2012, and rapidly increased during 2012-2019. The most significant lake expansion occurred in sub-region I, which is the source region of the Yangtze River Basin. There was a sharper increase during 2012-2019 than during 2000-2012 in sub-region II (the source region of the Yellow River Basin and the Qinghai Lake Basin) and sub-region III (the Qaidam Basin). The significant lake expansion occurred about 12 years earlier in sub-region I than in sub-regions II and III. This dramatic change in the lake area was closely associated with the annual precipitation, and precipitation was the primary driving factor. Although serious glacier retreat occurred, most of the lakes in the sub-regions were non-glacier-fed lakes. The correlation between glacier ablation and the change in the lake area was poor, which suggests that glacial meltwater was not the replenishment source of most of the lakes in this region. A more accelerated increase in the active layer thickness occurred (1.90 cm/yr), which was consistent with the more rapid lake expansion, and the permafrost degradation further intensified the lake expansion.

The frequency and the intensity of extreme temperature events have both increased globally because of the effects of climate warming. Such extreme events should be distinct in high-elevation areas owing to the phenomenon of elevation-dependent warming; however, corroborating evidence remains limited because of scarce observations. This study used the percentile method to identify annual extreme temperature events recorded in the delta O-18 of the Laohugou ice core (1960-2006) retrieved from the high-elevation area of the northeastern Tibetan Plateau (NETP). Comparison of these events with synchronous observations obtained at surrounding meteorological stations indicated that extreme temperature events identified from the ice core corresponded well with most temperature observations from the meteorological stations, suggesting that the delta O-18 record could be considered a reasonable proxy for regional temperature. However, occasional discord between the ice core and station records might reflect specific climatic shifts. Using circulation synthesis, the influencing circulation mechanism of each event was determined on the basis of differences in atmospheric parameters between each event and the average climatic state during 1970-2000. A double blocking high with warming over the Ural Mountains and east of Kuril-Kamchatka resulted in Eurasian warming, which transported warm air to the NETP and triggered the extreme high-temperature events. Conversely, a polar vortex in the Arctic led to a cold low over Eurasia, which transported cold air to the NETP causing extreme low-temperature events. The finding that variation of the Arctic air mass triggers extreme temperature events at high elevations in the NETP provides crucial insight for improved comprehension and forecasting of regional extreme temperature events.

Cloud is an active component in the weather-climate system that modulates both the radiation balance and the water cycle of the earth system via physical, chemical, and radiative mechanisms. In this study, we used observations of meteorological variables recorded on the Laohugou Glacier No. 12 in the western Qilian Mountains during 2009-2017 to investigate the radiative properties of cloud and its impact on glacier melting. The quantified cloud fraction showed an evident seasonal cycle. The highest cloudiness typically occurred at 16:00 Beijing time, which was probably associated with the strength of local convection that produced frequent occurrence of low-level cumulus or cumulonimbus clouds. Most heavy precipitation events (>14 mm) occurred on overcast days, signified that at least half of the total precipitation could be attributed to transportation from meso- or large-scale atmospheric circulations. Relationships between modelled glacier melting, energy components and cloud fraction showed that clouds could importantly reduce glacier melting, the most important contributor to this process was the clouds impact on net shortwave radiation. Circulation analyses showed that similar to 7.8%, similar to 6.3%, and similar to 18.7% of overcast days could be clearly and uniquely attributed to Arctic air mass events, monsoon events, and westerlies events, respectively. The remaining overcast days (similar to 67.2%) were influenced by multiple circulations, e.g., westerlies-monsoon, westerlies-Arctic air mass, monsoon-Arctic air mass, and westerlies-monsoon-Arctic air mass interactions. Monsoon potentially contributes a lot to precipitation in the western Qilian Mountains, future work should aim to do more atmospheric circulation analyses combining with isotopic tracing when precipitation occurs during overcast days.