The PCR-GLOBWB model was employed to simulate monthly runoff processes in the Yangtze River Basin under natural conditions and human-influenced scenarios. The Mann-Kendall mutation test was applied to delineate the baseline period and the impacted period. Based on standardized runoff index and generalized extreme value distribution, the range of extreme high flow and extreme low flow changes under two scenarios with different recurrence periods was calculated, and quantitatively evaluated the contribution of climate change and human activities to the evolution of extreme runoff in the Yangtze River Basin. The results indicate that climate change is the main contributing factor to the extreme high and low flow changes in the Yangtze River Basin. Climate change has intensified the severity of extreme high flow and l extreme low flow in the central part of the upper reaches and middle and lower reaches of the Yangtze River. The regional differences in the impact of human activities on extreme high flow and l extreme low flow are significant, alleviating the severity of extreme high currents in the Danjiangkou Reservoir and Sichuan Basin, but exacerbating the severity of extreme low flow in the middle and lower reaches.

Based on the meteorological data of the Yellow River Basin from 1961 to 2022, the trends and abrupt changes in temperature and precipitation were analyzed. Using the standardized precipitation evapotranspiration index (SPEI) as the drought indicator, the annual-scale variations in meteorological drought characteristics and drought recovery features in the Yellow River Basin were studied. The run theory was employed to extract drought characteristic indexes and drought recovery characteristic indexes, while the Mann-Kendall trend test method was applied to analyze the drought index and drought recovery characteristics in the Yellow River Basin from 1961 to 2022. The results indicate that the climate of the Yellow River Basin is complex, with uneven spatiotemporal distribution of drought indexes. From 1961 to 2022, meteorological drought showed a significant increasing trend in the lower reaches of the Yellow River Basin, while in most areas of the upper and middle reaches, meteorological drought exhibited a decreasing trend, with a minority of areas showing an increasing trend. The drought recovery rate demonstrated a significant increasing trend in the lower reaches of the Yellow River Basin, whereas in most areas of the upper and middle reaches, the drought recovery rate displayed a decreasing trend, with a minority of areas showing an increasing trend. Precipitation and temperature are identified as important factors influencing drought conditions in the Yellow River Basin, with precipitation playing a relatively more significant role.

To fully reveal multi-dimensional meteorological drought characteristics in China under changing environment, an SPI-RRV index-based drought risk assessment method was put forward by coupling the meteorological drought index(SPI) and the reliability-resilience-vulnerability(RRV) index to assess spatio-temporal evolution characteristics of meteorological drought and the drought risk in China. The results show that the SPI-RRV index has characteristics of high stability and strong spatio-temporal comparability, and can accurately assess spatio-temporal evolution characteristics of meteorological drought risk. The average drought grid ratio, proportion of drought months, and number of drought events in southem China are larger than those in northem China. Droughts in humid and semi-humid regions have higher intensity and shorter durations, while droughts in semi-arid and arid regions have lower intensity and longer durations. The transfer of high drought risk areas has a significant interdecadal variation pattern, with a transferring trend from northwest to southwest.

In view of the frequent occurrence of extreme weather events in the world, the isometric quantile method was adopted to build the high-precision precipitation and temperature database of CMIP6. Coupled with Palmer drought index (PDSI), the spatiotemporal evolution of global and arid zone drought characteristics under future scenarios (SSP1-2.6, SSP2-4.5, SSP3-7.0, SSP5-8.5) was estimated. The results show that the simulation accuracy of CMIP6 with bias correction is significantly improved. In the base period (1979-2014), the global drought frequency changes slightly, the global drought duration and drought intensity are relatively strong, and the drought intensity in the arid zone is relatively weak. During the forecast period (2025-2060), the global drought characteristics have significant differences in spatio-temporal distribution, with higher drought frequency, increased average drought duration and increased average drought intensity. In the forecast period, the frequency, duration and intensity of drought in the arid zone will increase, and the trend of drought in the tropical/subtropical arid zone and the temperate arid zone will become more obvious.

Frequent drought has posed widespread, large-scale and extremely severe impact on the ecological environment under global climate and human activities. This study aims to analyze the spatiotemporal dynamic evolution of drought in China. A threshold of -0.5 was chosen to identify drought conditions. A raster was set as the drought state at standardized precipitation evapotranspiration index (SPEI) less than -0.5. The start and end times of drought were varied for each raster within a single event, indicating the dynamic and evolving drought. At the same time, some rasters exited the drought states, while others entering. The contribution rates of drought to rasters were calculated at a given time, in order to capture the dynamic changes in drought. Three perspectives were considered: the extent of drought impact, duration, and severity. The SPEI was then used to assess the drought, in order to introduce the concept of persistent drought rasters. Large-scale and persistent drought events were identified to investigate the spatiotemporal dynamic evolution from 1961 to 2020, together with their response mechanisms to the atmospheric circulation. The research findings can be summarized as follows: 1) A total of 47 events occurred between 1961 and 2020. The 1970s witnessed the highest frequency of large-scale persistent drought events, with 10 occurrences, while the 2000s and 2010s each experienced 9 such events. The average duration of these drought events was 7.14 months, with the longest average duration in the 1960s at 11.83 months. The average extent was 28.66%, with the highest average extent index reaching 33.75% in the 2000s.The average severity was -2.86 for the 47 large-scale persistent drought events. Between 1980 and 2010, the average area affected by persistent drought events each decade showed a continuous expanding trend. Between 1970 and 2020, the average duration of persistent drought events each decade was concentrated between 4 to 8 months. 2) Before the 1990s, the lag time of Oceanic Niño Index's impact on spring precipitation was 3 and 9 months. From then on, the ONI's influence on summer and autumn precipitation extended to 6, 9, and 12 months. Once La Niña events occurred, there was the decrease in the spring precipitation, thereby increasing the frequency of spring droughts in China. 3) There was a resonance period of 16-48 months between ONI and SPEI3 during the years 1961-1976, 1980-1988, 1994-2001, and 2006-2020. The ONI index also demonstrated the strongest correlation with SPEI3 in this timeframe. While the WP index exhibited the weakest correlation with SPEI3 during the same periods.The research results help further understand the causes and patterns of drought in China, thereby enhancing the scientific basis and precision of drought prevention and mitigation policies.

To study the changes of drought characteristics in the propagation from meteorological drought to hydrological drought in the Yellow River Basin in the future, it is urgent to study the characteristics and transmission process of drought, so as to provide guidance for drought early warning. In this paper, the variable infiltration capacity (VIC) model was used to simulate the hydrological process of the Yellow River Basin in the historical period (1961-2014) and the future period (2015-2100), and the drought intensity propagation index and the drought duration propagation index were constructed based on the matching of drought events, and the changes of the drought characteristics propagation in the Yellow River Basin in the future compared with the historical period were analyzed. The conclusion shows that climate change has shortened the drought propagation time in the Yellow River Basin and in the future scenario, meteorological drought translation rate and hydrological drought sensitivity are higher than those in the historical period; thus, meteorological drought is more likely to spread to hydrological drought. The intensity of drought intensity propagation in the future period will remain basically unchanged, while the intensity of drought duration propagation will decrease significantly in the future.