Differential causal responses of four grassland types to hydrothermal drivers on the Qinghai-Tibet Plateau

Grasslands on the Qinghai-Tibet Plateau (QTP) are sensitive to climate change, but their causal responses to hydrothermal drivers and the dominance of temperature or water remain unclear. Combining 2000–2023 MODIS NDVI, evapotranspiration (ET), soil moisture (SM), monthly precipitation (PRE), and monthly mean (TMP), maximum (TMAX), and minimum (TMIN) temperatures, we applied Mann-Kendall trend analysis, generalized linear model (GLM), and convergent cross-mapping (CCM) with false nearest neighbors optimization to examine responses of alpine meadow, alpine grassland, temperate grassland, and desert grassland. The results show that (1) growing-season NDVI rose across the QTP, with a clear type-specific: desert grassland (60.29%) > temperate grassland (39.18%) > alpine grassland (28.51%) > alpine meadow (15.24%). (2) GLM (pseudo-R 2 > 0.5 over about 74% of the area) revealed type-specific response patterns. ET and PRE were positive on alpine and desert grassland (>51% of pixels) but negative on alpine meadow and temperate grassland (>50%); SM was broadly positive except in desert grassland; TMAX was negative across types, while TMIN was positive in all four. These reversals confirm that the four grassland types differ systematically in their response directions to hydrothermal drivers. (3) CCM showed temperature as a dominant region-wide driver (>93% of pixels), while the dominant water driver differed by types: SM for alpine meadow (91.79%) and temperate grassland (93.38%), PRE for alpine grassland (84.39%), and ET for desert grassland (74.97%). These findings clarify temperature drives overall QTP grassland changes, while water's dominant effect varies by type, supporting type-specific conservation and adaptive management under rapid climate change.