Hanjiang River Basin is an important water source area in China, and studying its precipitation characteristics is of great significance for flood prevention and drought resistance. Based on the daily precipitation data of 62 stations in the Hanjiang River and NCEP/NCAR reanalysis data, the intraseasonal variation characteristics of the precipitation over the Hanjiang River from August to October in 2021 and its relationship with atmospheric circulation and sea surface temperature were studied by using percentile, correlation methods and T-N wave activity flux. The results show that the record-breaking precipitation in the Hanjiang River during this period occurred in the upper reaches of the basin, characterized by extreme intensity and large total precipitation. Precipitation was above normal in both the summer and autumn periods, but the rainy regions in autumn were positioned further to the north. In summer, the energy of Rossby waves dispersing eastward from the North Atlantic through Siberia maintained a “two-troughs-two-ridges” pattern over Eurasia, bringing strong cold air. Affected by the strengthening and westward extension of the subtropical high in the western Pacific, moist water vapors were transported to the north through the southwest and eastward water vapor channels. The old and warm air confronted and converged on the south side of the upper-level jet stream, resulting in abnormally high precipitation. In autumn, the energy from Rossby waves dispersing from the North Pacific maintained a “two-troughs-one-ridge” circulation pattern over Eurasia, with relatively weaker cold air. The breaking of the subtropical high in the western Pacific led to southern water vapor channel. The northward movement of the high-altitude jet stream caused the convergence of cold and warm air to rise northward, resulting in the northward movement of above-average precipitation. The abnormal precipitation during summer in 2021 in the Hanjiang River Basin was influenced by the positive anomalies in sea surface temperatures in the tropical eastern Atlantic, while the autumn was influenced by the cold sea surface temperatures in the central equatorial Pacific.

The frequent occurrence of extreme climate events caused by global climate change has become a common challenge for scientific community and human society. Due to diverse driving factors and complex spatio-temporal processes, there are significant differences in various regions of the world. Based on the daily precipitation, temperature and other observation data of 76 national meteorological stations in Hubei from 1961 to 2022, the regional hot and drought events in Hubei since 1961 are identified according to the regional hot process monitoring index and the regional drought process monitoring evaluation method. On this basis, the change characteristics of frequency, duration, intensity and influence of the events are analyzed. The results show that regional hot events increase in frequency and intensity, and occur year after year. The change trend of regional drought event frequency is not significant, but it presents a characteristic of mass, continuous and repeated occurrence. Compound hot and drought events increase significantly and their intervals are shortened. The comprehensive intensity of the hot process in the summer of 2022 is the strongest since 1961, which superimposes with the drought in the Yangtze River Basin, producing a chain complex impact from meteorological drought to hydrological drought, agricultural drought and socio-economic drought. Under the background of global warming, the frequent occurrence of extreme hot, drought, compound hot and drought events might become a new normal of climate in Hubei. It is urgent to strengthen the research on the causes of extreme events and disaster risk assessment, and improve the ability to cope with extreme hot, drought and their compound disasters.

 Based on daily precipitation data at 700 meteorological stations of the Yangtze River basin from June to August during 1961-2017, the areal precipitation in each sub-zone was calculated by using Thiessen polygon method, and converted to normal distribution by using Box-Cox transformation. The thresholds of extreme precipitation events in summer were determined by using percentile method in each sub-zone of the Yangtze River basin. And on this basis, the temporal and spatial distribution characteristics of summer extreme precipitation events in each sub-zone and their spatial relationships of precipitation among sub-basins were studied. The results are as follows：(1) The decadal characteristic of summer extreme precipitation events in the Yangtze River basin was obvious. The extreme rainless events occurred frequently in the 1960s and 1970s, and the extreme rainy events dominated in the middle and lower reaches of the Yangtze River, while the extreme rainless events dominated in the upper reaches in the 1980s and 1990s. Since the 21st century, the large-range extreme rainless events dominated and occurred mainly in the upper reaches, while the extreme rainy event was easily to occur in Shigu of Jinsha River and above. (2) The first mode of summer extreme precipitation decomposed by EOF was consistently negative in most parts of the Yangtze River basin except for the east of Mintuo River, the north of Jialing River and the south of Poyang and Dongting Lakes during 1961-2017, vice versa. The second mode appeared opposite phases in the north and the south of the Yangtze River basin. (3) When the precipitation was extremely more in summer in the Yangtze River basin, the spatial distribution of summer precipitation had obvious differences and appeared four kinds of patterns, but the precipitation was easily more in the main streams of the Yangtze River. When the extreme rainless events occurred in summer, the precipitation was consistently less in most sub-zones, while for Mintuo River and Jialing River or the south of two lakes it was more.