## 2 Materials and Methods  
### Study Area  
Southwestern China (SWC), home to the country's second-largest natural forest expanse, spans a wide range of altitudes and features a diverse and complex climate [20]. This region also serves as a significant carbon sink for the nation [21]. The topography of SWC comprises three primary geomorphological units: the Hengduan Mountains (HDMs), with elevation exceeding 3000 m; the Yunnan-Guizhou Plateau (YGP), situated between 1000 and 3000 m; and the Sichuan (SCB) and Guangxi (GXB) basins, both below 1000 m. This varied landscape results in a wild range of climatic conditions, from the subtropical monsoon climate in the southeast to the Tibetan Plateau climate in the northwest [22]. The geographic and climatic diversity of SWC makes it an ideal region to study ecosystem responses to extreme climate events [23; 24]. By leveraging these differences in both topography and climate, this study aims to distinguish the effects of ECIs across regions with distinct environmental conditions. Beyond altitude, the analysis also considers broader geographic and climatic variations that influence ecosystem sensitivity and resilience to extreme events.  
SWC encompasses Sichuan Province, Chongqing Municipality, Yunnan Province, Guizhou Province, and the Guangxi Zhuang Autonomous Region, covering a total area of approximately 1.37 million square kilometers. Based on geographic terrain and climate, the region can be divided into four distinct subregions: the HDMs, SCB, YGP, and GXB (Figure 1a) [22; 25].  
Figure 1: Distribution of elevation, and meteorology station and land cover types in SWC, with data on mean annual temperature and annual precipitation at meteorological stations. (**a**) Distribution of elevationand meteorological stations in south-western China, with regional divisions according to geographical relief. (**b**) Vegetation cover in south-western China and administrative boundaries. (**c**) Annual mean temperature at each station and standard deviation between stations from 1982 to 2019. (**d**) Total annual precipitation at all stations and standard deviation between stations from 1982-2019.  
The HDMs are characterized by a rugged topography with significant vertical relief, experiencing dry winters and wet summers. The YGP features high elevations in the north that gradually decrease toward the south, with a warm and humid climate. The SCB, surrounded by mountain ranges, experiences hot and humid summers. The GXB, partially influenced by its coastal proximity, benefits from generally favorable climatic conditions. The geographic and climatic variability across these subregions contributes to the diverse vegetation distribution patterns throughout SWC (Figure 1b). Temperature and precipitation in the region are highly variable over space and time. Using meteorological data (1980-2019) from 122 stations in the region, the average annual temperature is around 15 \({}^{\circ}\)C. There is also variation in annual precipitation, with mean annual temperatures of 12.28 \({}^{\circ}\)C, 16.26 \({}^{\circ}\)C, 16.66 \({}^{\circ}\)C, and 20.82 \({}^{\circ}\)C for the HDMs, YGP, SCB, and GXB, respectively, and a mean annual precipitation of 981.5 mm, 1197.4 mm, 1122.4 mm, and 1547.7 mm, respectively, indicating that there is a great deal of climatic variability in the region (Figure 1c,d).