Characteristics of ground surface heat flux for alpine vegetation in freeze-thaw cycles in the three river source region

Ground surface heat flux (G0) is a key component of surface energy flux and serves as a reliable parameter for assessing shallow geothermal energy. Using the observations from four sites and a novel method, we investigated the daily, monthly, and diurnal characteristics of G0 across various types of land cover in the Three River Source Region. The contribution of soil heat flux at 5 cm or 7.5 cm (Gsoil) to G0 was found to be only between 1/2 and 2/ 3, with the remaining portion being attributed to changes in heat storage of soil and liquid water (Delta ssoil), heat storage of soil ice (Delta sice) and latent heat of ice phase change (Delta sLH). The characteristics of G0 exhibited significant variations in response to different land-covered vegetation during daily, monthly, and diurnal cycles, as well as two freeze-thaw stages. The alpine marsh-covered soil had the largest annual amplitude in G0 on both daily and monthly averages but showed the smallest diurnal amplitude in G0. In the frozen stage (FS), G0 played a significant role as a supplement to net radiation (Rn) in TRSR, particularly in the alpine marsh region where it accounted for approximately -22 % to -80 % of Rn from November to February.