Assessments on surface water resources and their vulnerability and adaptability in China
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.