A revised Köppen climate classification reveals hydrothermal controls on eco-climate over the Qinghai–Tibet Plateau

The Köppen–Geiger climate classification is widely used to represent global eco-climatic patterns, yet its application to high-altitude regions such as the Qinghai–Tibet Plateau (QTP) remains limited because tundra climates (ET) are defined primarily by temperature, overlooking moisture constraints on vegetation. Here we present a revised Köppen–Geiger framework that incorporates the aridity index (AI) as an intermediary to represent coupled hydrothermal conditions while preserving the original temperature–precipitation structure. This refinement subdivides the ET climate into three sub-classes: arid (ETw), semi-arid (ETm), and semi-humid (ETf) tundra. Validation against satellite-derived NDVI shows improved correspondence with vegetation patterns. The revised classification reveals systematic reorganization of climate zones across the QTP, highlighting the role of coupled thermal and moisture constraints in shaping eco-climatic gradients under recent climate change. More broadly, this approach provides a transferable pathway to refine climate classifications in high-altitude and cold–dry regions where temperature-based schemes alone are insufficient.