Based on ground meteorological observations and land surface reanalysis data, flash drought and high temperature events in the Yangtze River Basin from 1950 to 2021 were identified, and the spatiotemporal distribution characteristics of these two extreme events were analyzed. Combined with the Copula function, the joint probability distribution and conditional probability distribution functions of high temperature and flash drought were constructed, and the onset time periods when the soil moisture content percentile reached moderate, severe, extreme, and excessively extreme droughts under different temperature conditions were estimated. The results show that the times of occurrence of flash droughts and days of high temperature have significantly increased since 1990. The onset time period of droughts is significantly negatively correlated with daily maximum temperature, and shortens as the temperature increases, indicating the higher likelihood of flash drought occurrence at higher temperatures. The joint probability of high temperature and flash drought in the upper and middle reaches of the Yangtze River Basin, including Yunnan, Sichuan, Chongqing, Guizhou, and Hubei, is higher than that in the downstream areas in typical events in 2006, 2011, and 2013. Under low temperature conditions, the onset time period of droughts in the source region of the Yangtze River Basin is twofold of that in the middle and lower reaches. With the rising temperatures, the onset time period of droughts in the source region and the upper reaches shortens. When the daily maximum temperature exceeds 30℃, the development of droughts shows a spatial pattern of rapid onset in the upstream and delayed onset in the downstream.

Vegetation is an essential component of the terrestrial ecosystem, which plays a crucial role in facilitating material and energy exchanges among the soil, water, and atmosphere. In the context of global warming, climate extremes such as drought and heatwave events become more frequent. These extreme events threaten vegetation growth, leading to vegetation degradation and causing serious impacts on the structure and function of the terrestrial ecosystem. With the weakening of vegetation resistance to extreme dry and hot events, it has also been challenging for it to recover to its original state. To better cope with the risks of ecosystem degradation in a warming environment, it is necessary to evaluate the spatiotemporal patterns of vegetation resilience and its variation tendency. In this study, we used the Global Orbiting Carbon Observatory-2 based Solar Induced chlorophyll Fluorescence (GOSIF) satellite gridded data at a spatial resolution of 0.05° and eight day-interval during 2000-2022 to analyze the trend and spatial patterns of vegetation resilience over China. Based on the concept of the critical slowing down, the lag-one autocorrelation (AC1) and variance were employed as two indicators of the early-warning signals for the critical transitions of vegetation state. On this basis, the Kendall test was used to examine the trend of vegetation resilience, and the k-means clustering method based on the elbow method was employed to classify the different types of vegetation resilience. The results showed that spatially the vegetation resilience over China generally presents a decreasing pattern from south to north. Spatially, the lowest vegetation resilience was found in the Yellow River Basin, while vegetation resilience was generally high in Southwest China such as Sichuan and Yunnan provinces, and eastern parts of North China. Except for the northern parts of the Heilongjiang province and Inner Mongolia, the trends indicated by the AC1 and variance series were generally similar, where the vegetation resilience in most regions over China presented a decreasing pattern during 2000-2022. Compared with the period of 2000-2010, grid cells with enhanced vegetation resilience decreased by 31.04%, and grid cells with weakened vegetation resilience increased by 24.28% during 2011-2022, mainly distributed in the Yellow River Basin, upper and middle reaches of the Yangtze River Basin, Pearl River Basin. A tipping point of the vegetation resilience over China on average occurred in 2013. According to the k-means clustering method, the variation patterns of vegetation resilience were classified into seven groups. The tipping points of vegetation resilience in southwestern China, southeastern coastal areas, and the Pearl River Basin occurred earlier than the national average, while the tipping points in mountain areas in southern China, the Yellow River Basin, central Inner Mongolia and northern Xinjiang were the same as the national average. In contrast, the tipping points of vegetation resilience at the junction of Inner Mongolia and northern Heilongjiang were later than the national average. The results have implications for understanding the temporal characteristics and spatial heterogeneity of vegetation resilience over China, which are also promising to provide some references for the vegetation ecological restoration and protection strategies in China.