Review on simulation of land-surface processes on the Tibetan Plateau

The Tibetan Plateau(TP) has powerful dynamics and thermal effects, which makes the interaction between its land and atmosphere significantly affect climate and environment in the regional or global area. By retrospecting the latest research progress in the simulation of land-surface processes(LSPs) over the past 20 years, this study discusses both the simulation ability of land-surface models(LSMs) and the modification of parameterization schemes from two perspectives, the models' applicability and improved parameterization schemes. Our review suggests that different LSMs can well capture the spatiotemporal variations of the physical quantities of LSPs; but none of them can be fully applied to the plateau, meaning that all need to be revised according to the characteristics specific to the TP. Avoiding the unstable iterative computation and determining the freeze-thaw critical temperature according to the thermodynamic equilibrium equation, the unreasonable freeze-thaw parameterization scheme can be improved. Due to the complex underlying surface of the TP, no parameterization scheme of roughness length can well simulate the various characteristics of the turbulent flux over the TP at different temporal scales. The uniform soil thermodynamic and hydraulic parameterization scheme is unreasonable when it is applied to the plateau, as a result of the strong soil heterogeneity. There is little research on the snow-cover process so far,and the improved scheme has no advantage over the original one due to the lack of some related physical processes. The constant interaction among subprocesses of LSPs makes the improvement of a multiparameterization scheme yield better simulation results. According to the review of existing research, adding high-quality observation stations, developing a parameterization scheme suitable for the special LSPs of the TP, and adjusting the model structures can be helpful to the simulation of LSPs on the TP.

Surface air temperature changes over the Tibetan Plateau:Historical evaluation and future projection based on CMIP6 models

With its amplification simultaneously emerging in cryospheric regions,especially in the Tibetan Plateau,global warming is undoubtedly occurring.In this study,we utilized 28 global climate models to assess model performance regarding surface air temperature over the Tibetan Plateau from 1961 to 2014,reported spatiotemporal variability in surface air temperature in the future under four scenarios(SSP1-2.6,SSP2-4.5,SSP3-7.0,and SSP5-8.5),and further quantified the timing of warming levels(1.5,2,and 3℃)in the region.The results show that the multimodel ensemble means depicted the spatiotemporal patterns of surface air temperature for the past decades well,although with differences across individual models.The projected surface air temperature,by 2099,would warm by 1.9,3.2,5.2,and 6.3℃relative to the reference period(1981–2010),with increasing rates of 0.11,0.31,0.53,and 0.70℃/decade under the SSP1-2.6,SSP2-4.5,SSP3-7.0,and SSP5-8.5 scenarios for the period 2015–2099,respectively.Compared with the preindustrial periods(1850–1900),the mean annual surface air temperature over the Tibetan Plateau has hit the 1.5℃threshold and will break 2℃in the next decade,but there is still a chance to limit the temperature below 3℃in this century.Our study provides a new understanding of climate warming in high mountain areas and implies the urgent need to achieve carbon neutrality.

Ground temperature variation and its response to climate change on the northern Tibetan Plateau

Ground temperature plays a significant role in the interaction between the land surface and atmosphere on the Tibetan Plateau(TP).Under the background of temperature warming,the TP has witnessed an accelerated warming trend in frozen ground temperature,an increasing active layer thickness,and the melting of underground ice.Based on high-resolution ground temperature data observed from 1997 to 2012 on the northern TP,the trend of ground temperature at each observation site and its response to climate change were analyzed.The results showed that while the ground temperature at different soil depths showed a strong warming trend over the observation period,the warming in winter is more significant than that in summer.The warming rate of daily minimum ground temperature was greater than that of daily maximum ground temperature at the TTH and MS3608 sites.During the study period,thawing occurred earlier,whereas freezing happened later,resulting in shortened freezing season and a thinner frozen layer at the BJ site.And a zero-curtain effect develops when the soil begins to thaw or freeze in spring and autumn.From 1997 to 2012,the average summer air temperature and precipitation in summer and winter from six meteorological stations along the Qinghai-Tibet highway also demonstrated an increasing trend,with a more significant temperature increase in winter than in summer.The ground temperature showed an obvious response to air temperature warming,but the trend varied significantly with soil depths due to soil heterogeneity.