A clear understanding of the changes of water resources under the background of environmental changes is of great significance for scientific management and utilization of water resources in China. This study systematically analyzed the spatial-temporal variations of surface water resources in China since 2000. Water vulnerability in current (2010s) and its trends from 2000 to late-2010s in different regions of China were also summarized. In addition, the correspondingly adaptive measures to counter regional risks to water resources were proposed. We concluded that the runoff of major rivers had been decreasing in eastern China and increasing in western China during 2000-2018. In the arid area of Northwest China, the alpine runoff has shown an overall upward trend since the late-1990s/early-2000s, with a 10%-25% increase caused by the increase of glacial meltwater and precipitation. While the runoff of each hydrological station in the 2000s-2010s was 34.7% lower than that in the 1950s-2010s on average. The increases in precipitation and glacial meltwater with global warming caused a rapid expansion of lakes in the Qinghai-Tibet Plateau and Xinjiang, thus leading to an increase in total area and water quantity of lakes in China from 1995 to 2015. The mean contribution rates of climate change and human activity to runoff change in river basins of China were 53.5% and 46.5%, respectively, during the period of 2000-2010s. The driving factor of runoff change in many river basins has gradually changed from climate change (1950s-2000) to human activity (2000-2018). During 2000-2018, the contributions of human activities to runoff change were 50%-80% in major rivers of eastern China. The vulnerability in most areas of Northwest China and North China is generally high, with the vulnerability index greater than 0.6. Comparatively, in Northeast, East, South, and Central China, it is lower or not vulnerable. In Southwest China, the vulnerability varies greatly with Yunnan and Sichuan relatively low while Chongqing and Guizhou relatively high. The precipitation increase, the application of water-saving technology, the establishment of flood control and drought relief engineering facilities, and the introduction of relevant policies and measures have helped to gradually reduce the vulnerability of water resources in most areas of North and Northwest China (except Xinjiang) from 2000 to 2010s. Water vulnerability has been increasing in southern China, caused by climate change and the development of industry and agriculture, which increases water resource exposure since 2000. Based on the typical risk factors and vulnerability characteristics of water resources in different regions, this study proposed some targeted adaptive measures correspondingly so as to scientifically deal with the problems of surface water resources in China.

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.