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he ' Scientific Understanding of Climate Change' part of China' s Fourth National Assessment Report on Climate Change reflects a series of new evidence and new understanding of climate change in China since 2015, based on scientific analyses such as climate system observations, paleoclimate archives, theoretical research, and climate modeling. This report summarizes the basic climatic variables of the atmosphere, ocean, cryosphere, and biosphere, as well as the characteristics of climate change seen in extreme events and typical regions in China. It also analyzes the changes in natural and human driving factors affecting climate change and estimates the future trends of climate change in China. Compared with the Third National Assessment Report on Climate Change, this paper identifies the new features of this assessment report in terms of the structure and conclusions. At the same time, it is pointed out that the system of China' s climate change assessment report is continuously enriched and the understanding of scientific basis is constantly deep -ened. The paper also makes a preliminary comparison between this report and the report of Working Group I to the Sixth Assessment of the Intergovernmental Panel on Climate Change (IPCC) and proposes solutions to issues concerning climate change monitoring and diagnosis, detection and attribution, simulation estimation, instruments, and methods that China may face in the future. [ABSTRACT FROM AUTHOR]

Extreme climate events and related risk exposures in Huang‐Huai‐Hai (HHH) river basin were projected under global warming of 1.5–2°C using the high‐resolution combined dynamical and statistical downscaling dataset. Firstly, evaluation indicated that the dataset can well reproduce the spatial distribution of all temperature extremes and most of the precipitation extremes, providing a reliable ability for future projections. Then, projections showed that the hot events were projected to increase, while the cold events were projected to decrease substantially in the whole HHH river basin for 1.5°C and 2°C global warming. The additional 0.5°C of warming roughly accelerated the increase of extreme temperatures by 0.6°C, and increased the number of heat days by 2.7 days. In addition, the rainfall events and the precipitation intensity were projected to increase while the drought events were projected to decrease, with the slight changes due to the additional 0.5°C warming. The gross domestic product (GDP) exposures to heat events and heavy rainfall increased more than nine fold for 1.5°C and 2°C global warming, while the growing population (POP) exposures to that increased by more than 100% and 20%, respectively. For the increased exposures to heat events, the changes in GDP (POP) were as important as changes in interaction effect between climate and GDP (POP), while the exposures to heavy rainfall events was mainly dominated by GDP (POP). In addition, the enhanced interaction effect was the most important factor to the increase of exposures due to additional 0.5°C of warming. Notably, the largest increases of heat events and heavy rainfall events were projected in Huaihe river basin due to the additional 0.5°C warming, accompanied by greatest increase of exposures, implying larger risk in the future. [ABSTRACT FROM AUTHOR]