With the warming of the climate, extreme heavy precipitation, droughts and floods frequently hit all parts of the world, and the earth's climate is in a "dire straits". In the early morning of July 26, a joint study by Chinese and British scientists published online in the top international academic journal Science pointed out that the global land precipitation variability has increased significantly over the past 100 years, and the reason for this is man-made greenhouse gas emissions.
In recent years, not only has "rain for the end of the year" become more common, but droughts have also worsened significantly in many parts of the world, severely affecting water and energy supplies and triggering disasters such as wildfires.
Are there patterns and trends to follow? What causes it? To this end, Zhang Wenxia, associate researcher and Zhou Tianjun of the State Key Laboratory of Atmospheric Sciences and Geofluid Dynamics Numerical Simulation of the Institute of Atmospheric Physics of the Chinese Academy of Sciences, cooperated with scholars from the United Kingdom Met Office to carry out relevant research.
"Warming has strengthened the global water cycle, which is reflected in an increase in global average precipitation and an increase in extreme precipitation over most regions." Zhou Tianjun, corresponding author of the paper, said that based on evidence from various studies, the scientific community has become more aware of the physical mechanisms of changes in average precipitation and extreme precipitation, and human activities have led to large-scale changes in land precipitation patterns, and extreme weather events, including heat waves, heavy precipitation and droughts, have become more frequent and severe.
At the same time, the global precipitation temper is becoming more complex and unpredictable. Scientifically, "precipitation variability" is used to measure the variation of precipitation fluctuations over time - the stronger the precipitation variability, the more uneven the distribution of precipitation over time, the more unstable the water supply, and the more intense the dry and wet oscillations, that is, "wetter in wet periods and drier in dry periods".
Zhang Wenxia, the first author of the paper, said that changes in the intensity of precipitation variability directly affect the climate resilience of societies and ecosystems, and although climate projection studies suggest that global precipitation variability will theoretically increase with future warming, there is no evidence that human activities have changed precipitation variability in practice.
In order to find evidence of precipitation variability, the research team used all publicly available daily precipitation observations in the world, and found through rigorous screening and systematic analysis that since 1900, about 75% of the world's landland precipitation variability has increased in regions with sufficient observational data, especially in Europe, Australia and eastern North America. On a global average, daily precipitation variability is increasing at a rate of 1.2%/decade.
The study found that the enhancement of precipitation variability can be attributed to anthropogenic greenhouse gas emissions, which is dominated by thermal action. Zhang Wenxia explained that the increase in atmospheric water vapor content caused by greenhouse gas warming is conducive to the increase of precipitation anomaly and variability. At the same time, changes in atmospheric circulation also affect precipitation variability on the interdecadal scale.
Zhou Tianjun mentioned that with the increasing variability of precipitation, the rapid turn of drought and flood in Henan this year will become more frequent and more intense in many parts of the world. "A series of impacts brought about by the increase in precipitation variability have been highlighted, and all sectors of society need to pay close attention to this." He believes that the increased variability of precipitation will have a profound impact on agricultural production, water resource management, ecosystem protection and social economy, and will also pose new challenges to disaster prevention and mitigation and climate change response.
This study provides a new understanding of the impact of global warming on precipitation, and provides new evidence for deepening the study of the multi-scale water cycle change mechanism.
Text: Xu Qimin
Photo: Unless otherwise noted, provided by the interviewee
Editor: Xu Qimin