*2.1. Study Area*

The Qinghai-Tibetan Plateau is situated in southwestern China and covers all of Tibet and the Qinghai provinces and is also a part of the Xinjiang, Sichuan, Gansu, and Yunnan provinces (Figure 1). The Qinghai-Tibetan Plateau is considered the third pole in the world, has an average altitude of >4000 m, and is characterized by a plateau monsoon climate with low temperatures, low precipitation, and strong insolation. More than 54% of the Qinghai-Tibetan Plateau area has a total annual precipitation below 400 mm and temperatures below 0 ◦C [22]. This region is known as the Asia water tower and is home to the headstreams of the Yangtze, Yellow, Lantsang, and Indus rivers. The alpine, cold, and dry climatic conditions lead to unique vegetation types on the Qinghai-Tibetan Plateau. A climate gradient exists from warm-humid in the southeast to cold-dry in the northwest, along which the vegetation types transition from forestland, meadow, steppe, and desert. The grassland, which includes meadow, steppe, and desert steppe, and covers 51.05% of the Qinghai-Tibetan Plateau area, is the most important ecosystem and sensitive to climate change. An understanding of grassland dynamics under the climate and human disturbance conditions is crucial for regional ecological security.

**Figure 1.** Study area and geographical subregions. The black circles represent the locations of 209 meteorological stations on the Qinghai-Tibetan Plateau.

We divided the entire Qinghai-Tibetan Plateau into 12 subregions (Figure 1, Table 1) based on the bio-geographical division proposed by Zheng et al. [30]. The grassland distribution was extracted according to a China vegetation map (scale = 1:100,000) [31], eliminating subregions X, XI, and XII, for which the main vegetation types are desert, forestland, and forestland, respectively. Only the remaining nine subregions (I–IX) are analyzed in this study, covering meadow, steppe, and desert grassland (Table 1). Of these nine subregions, we focused in detail on subregion I, which has the highest annual accumulated temperature above 0 ◦C (AGDD0) and medium moisture index (MI). Subregions II and III had relatively high MI values that decreased from southeast to northwest. Each subregion exhibited unique climatic conditions and economic development levels, as well as different vegetation responses to climate and human activities.


**Table 1.** Description of the Qinghai-Tibetan Plateau subregions. AGDD0: Annual accumulated temperature above 0 ◦C. MI: Moisture index calculated by the ratio of the mean annual precipitation to the annual equilibrium evapotranspiration.
