Glacier type transformation trends in China over 1981–2019 based on Shi‒Xie classification framework

Glaciers worldwide are undergoing rapid retreat, yest changes in their glaciological and climatological characteristics remain poorly quantified at large spatial scales and cross different glacier types. Previous studies have primarily relied on limited observations and samples, leaving the spatial patterns and processes of glacier-type transformation insufficiently understood. China, which hosts extensive glacierized regions spanning extremely continental to maritime environments, provides an ideal setting to address this gap. Using the Shi‒Xie glacier classification framework, we analyzed equilibrium-line altitude (ELA) and five indicators (annual and summer air temperature, annual precipitation, and 20 m ice temperature at the ELA, along with maximum surface velocity) for 2449 glaciers during 1981–2000 and 2001–2019. The results reveal systematic but regionally differentiated transformation patterns. Extremely continental glaciers show localized shifts toward subcontinental conditions along their margins, associated with warming and increased precipitation. Subcontinental glaciers exhibit highly heterogeneous responses, with tendencies toward more continental characteristics in the Karakoram and western Himalaya, but weak or limited transformation in the Tien Shan. Maritime glaciers display a coherent shift toward subcontinental conditions, characterized by widespread below-threshold thermal and dynamic indicators. These findings demonstrate that glacier-type transformation is already underway across glacierized regions in China but occurs as a gradual and spatially heterogeneous process. The multi-indicator framework and transformation index enable detection of early-stage transformation signals before full threshold crossings, extending previous boundary-based approaches and providing a more comprehensive and process-informed perspective on glacier evolution under climate change.