Spatial-temporal evolution of compound dry-hot events and their effects on vegetation vulnerability in Inner Mongolia Grassland

Compound extreme climate events refer to two or more climate events that occur simultaneously or consecutively, and they cause more severe negative impacts compared with single extreme climate events. Therefore, this study selects the compound dry-hot event as the research object. In this study, the standardized compound drought and heat index (SCDHI) to identifies compound dry-hot events and the different Copula functions are selected to explore the response of vegetation vulnerability for compound dry-hot events in Inner Mongolia grassland. The results indicate that: (1) the inter-annual variation of NDVI in Inner Mongolia showed a significant upward trend with 0.003/a, and a mutation occurred in 2017. It has "low in the southwest and high in the northeast" spatial distribution pattern. (2) The SCDHI constructed in this study can effectively represent the compound dry-hot event in the Inner Mongolia grassland. The Inner Mongolia grassland exhibits the short duration, low intensity, and medium to high severity characteristics. (3) Under the same compound event stress, the vegetation loss rate becomes more severe as the NDVI percentile decreases. There were significant differences in vegetation loss rates among different vegetation types during their respective growing seasons. The results of this study can provide scientific evidence for exploring the impact of extreme compound dry-hot events on vegetation.