The vegetation and ecosystem in the source region of the Yangtze River and the Yellow River (SRYY) are fragile. Affected by climate change, extreme droughts are frequent and permafrost degradation is serious in this area. It is very important to quantify the drought–vegetation interaction in this area under the influence of climate–permafrost coupling. In this study, based on the saturated vapor pressure deficit (VPD) and soil moisture (SM) that characterize atmospheric and soil drought, as well as the Normalized Differential Vegetation Index (NDVI) and solar-induced fluorescence (SIF) that characterize vegetation greenness and function, the evolution of regional vegetation productivity and drought were systematically identified. On this basis, the technical advantages of the causal discovery algorithm Peter–Clark Momentary Conditional Independence (PCMCI) were applied to distinguish the response of vegetation to VPD and SM. Furthermore, this study delves into the response mechanisms of NDVI and SIF to atmospheric and soil drought, considering different vegetation types and permafrost degradation areas. The findings indicated that low SM and high VPD were the limiting factors for vegetation growth. The positive and negative causal effects of VPD on NDVI accounted for 47.88% and 52.12% of the total area, respectively. Shrubs were the most sensitive to SM, and the response speed of grassland to SM was faster than that of forest land. The impact of SM on vegetation in the SRYY was stronger than that of VPD, and the effect in the frozen soil degradation area was more obvious. The average causal effects of NDVI and SIF on SM in the frozen soil degradation area were 0.21 and 0.41, respectively, which were twice as high as those in the whole area, and SM dominated NDVI (SIF) changes in 62.87% (76.60%) of the frozen soil degradation area. The research results can provide important scientific basis and theoretical support for the scientific assessment and adaptation of permafrost, vegetation, and climate change in the source area and provide reference for ecological protection in permafrost regions.

For a comprehensive response to climate change and low carbon development mode, the 3S-based regional terrestrial carbon cycle model in Luanhe basin is constructed in accordance with componentbased development strategy to identify carbon cycle evolution of terrestrial ecosystem under the background of local changes, combining measured weather data, prototype observation data of soil and plants as well as remote-sensing information in different spatial and temporal scales. The model has the ability of describing canopy fluxes, net primary productivity, biomass allocation and turnover, mortality, decomposition of soil organic matter and other dynamic processes. The carbon cycle evolution in Luanhe Basin from 1995 to 2010 is simulated and analyzed. The results are shown as follows: 1) in the temporal scale, inter-annual change of leaf area index with a slight growth trend is larger than that of net primary productivity (NPP), ground and underground biomass and soil carbon content; 2) There are obvious regional differences in spatial view, spatial distribution of results are consistent with those of watershed plant and soil, displaying the characteristics that the above major variables of mountainous regions in middle-upper reaches are greater than those of grassland meadows in the upstream and plains in the downstream.

In the context of global climate change, droughts are expected to become more severe, persistent, and frequent. Drought is considered to be one of the main drivers of vegetation mortality, and the mechanism of vegetation response to drought has been the focus of global attention. This paper analyzes the research hotspots on vegetation response to drought at internal and international through bibliometric analysis, summarizes the progress of drought assessment in the alpine plateau region on this basis, and further analyzes the mechanism of vegetation response to drought from the perspectives of vegetation structure and physiological changes, vegetation water recharge, and ecosystem stability. The objective of this paper is to provide a comprehensive overview of the research conducted on the impact of drought on vegetation in the alpine plateau region. Additionally, the paper will discuss the existing challenges and limitations of this research, as well as offer insights into future directions and trends in this field. This paper aims to serve as a valuable reference for researchers, establish a foundation for further research and decision-making in the alpine plateau region, and contribute to the advancement of research in this field.