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Winter warming is fast than summer warming on the Qinghai-Tibet Plateau (QTP). However, no assessment of winter warming effects on permafrost has been attempted. Here we conducted hypothetical control experiments and used the Noah land surface model to evaluate the impacts of winter warming on the QTP permafrost. The results show that air temperature in winter (November-April) was increasing at a rate of 0.66°C/decade during 1980s−2000s, over double that in summer (May-October). The mean annual ground temperature of permafrost increased by 0.13°C/decade. The summer warming dominated the variations in thermal regime of permafrost before 2000. After that, the influence of winter warming on permafrost thermal regime has gradually grown and exceeded that of summer warming. Winter warming has amplified the thermal degradation of permafrost. Our findings reveal that alpine continuous permafrost on the northern QTP has experienced a prominent regional warming due to rapid winter warming since 2000. Plain Language Summary As the highest and largest permafrost region in mid-latitudes,Qinghai-Tibet Plateau (QTP) has experienced prominent winter warming in the past three decades. To date, no study has been made to assess the impacts of winter warming on the QTP permafrost. We used the Noah land surface model to investigate this effect, based on controlled experiments including a baseline representing historical climate conditions and two intentionally constituted hypothetical experiments that remove the winter (November-April) or summer (May-October) warming from the historical records. We analyzed the seasonal changes in air temperature, evaluated the effects of winter and summer warming on the changes of frozen ground in terms of several key indicators (including active layer thickness, permafrost area, mean annual ground temperature of permafrost, and maximum freezing depth of seasonally frozen ground) and investigated the possible underlying mechanism of winter warming on permafrost. The results indicate that winter warming accelerates permafrost thermal degradation. Especially since 2000, alpine continuous permafrost on the Qiangtang High Plain, Northern QTP, has undergone an obvious regional warming induced by rapid winter warming.

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As a unique geomorphological unit on Earth, the Qinghai-Tibet Plateau (QTP) is sensitive to global warming, and has warmed twice as fast as the global average over the past five decades (D. Chen et al., 2015;Yao et al., 2019). The QTP, known as the "Third Pole," has the largest area of alpine permafrost in the world (Jin et al., 2000). Permafrost on the QTP has been observed to have degraded substantially as a result of drastic climate warm-

The Qinghai-Tibet Plateau (QTP), the highest plateau in the world with an average elevation of over 4,000 m above sea level (a.s.l.), is characterized by unique topography and geographical location. It is thus known as the "Third Pole." Its thermal and dynamic effects exert profound influence on the regional climate and even the global climate system (Duan & Wu, 2005;Yanai et al., 1992). Many important Asian rivers originate from the QTP, including the Yangtze River, the Yellow River and the Mekong River. It holds the largest ice storage after the polar regions, dubbed as the "Asian Water Tower." It drains a lot of water to rivers and is particularly crucial for water resources on the Asian continent (Immerzeel et al., 2010;Xu et al., 2008;Yao et al., 2019). The QTP covers an area of approximately 2.6 × 10 6 km 2 , half of which is underlain by permafrost and accounts for 75% of alpine permafrost in the Northern Hemisphere (Jin et al., 2000).