The ecological carrying capacity (ECC) is a barometer for ecosystem sustainability. Alpine grassland ecosystems are thought to be the most sensitive ecosystems to climate change. Yet, the ECC of alpine grassland is less well understood. This study aims to establish a structural dynamics model that it enables us to capture different states, changes in tendency, as well as major driving variables of alpine grassland ECC. The results showed that the active layer thickness had a significant adverse effect on ECC (p = 0.05), while precipitation, air temperature, net primary productivity (NPP) had a significant positive effect on ECC (p = 0.01). And anthropogenic factors like fenced pasture, warm shed area, sown grassland area, and livestock density also caused an increase in ECC (p = 0.05). The ECC of alpine grassland displayed an increasing trend on the Qinghai-Tibetan Plateau (QTP). The mean contributions of active layer thickness, NPP, precipitation, and air temperature to the ECC were - 10.0% (p = 0.05), 52.1% (p = 0.01), 17.0% (p = 0.01), and 12.0% (p = 0.01), respectively. From 1980 through 2013, the average annual growth of ECC was 9.1%. The sensitivity of the grassland ECC to major climate variables fluctuated, with periods of high and low sensitivity recorded. On a geographical scale, the Tibet Autonomous Region had higher levels of sensitivity to change, with larger fluctuations, in comparison with Qinghai Province. These findings could provide an important basis for effective adaptation of alpine ecosystem to climate change.

The study of the diurnal response mechanism of the actual evapotranspiration (ETa) to the environment in the permafrost regions of the Qinghai-Tibet Plateau (QTP) using the LYS30 micro-evaporation instrument found that there are different feedbacks to the ETa under freezing and thawing cycles. The ETa process during the winter cooling period (WC) and the spring warming period (SW) is snow and ice sublimation and is mainly affected by the vapour pressure deficit (VPD). In the summer thawing period (ST), ETa can reach the maximum value when all meteorological elements reach a certain range of change at the same time, while ETa will decrease when the meteorological elements are not qualified. During the autumn freezing period (AF), the amount of condensate reached a maximum at 7:00, and due to the sudden change in meteorological elements at 9:00, the ETa increased rapidly at a rate higher than the condensation rate that occurred between 7:00 and 9:00. We also found that in different stages of freezing and thawing, the two physical processes of condensation and evaporation alternated in 1 day, with the process of evaporation occurring during the day and the condensation process occurring during the night. The diurnal response mechanism of the ETa to the environment in the permafrost regions of the QTP is expected to reveal the mechanism of soil hydrological processes and will provide a theoretical and scientific basis for water balance analysis and ecological environment protection in permafrost regions.