Observed surface heat fluxes partitioning during the local growing season over the Tibetan Plateau

Abstract

Turbulent heat fluxes across the surface are an important mechanism of land-atmosphere coupling. But there is still a lack of sufficient observational measurements, particularly over the climate sensitive Tibetan Plateau (TP). This paper examines the partitioning between sensible and latent heat fluxes during growing season using the Bowen ratio as a diagnostic based on eddy covariance measurements from 12 observational sites located on the TP with the altitudes ranging between 3327 m and 4509 m above sea level. The results show an average Bowen ratio of 1.13, indicating that sensible heat flux is only slightly dominant in surface energy balance. For different climate zones, Bowen ratio varies from 0.56 to 1.05 in the semi-arid zone, 0.53 and 0.57 in the subhumid region, and 2.73 to 3.11 in the arid zone. The Bowen ratio shows sensitivity to soil dry and wet condition, with higher values during drier soil conditions. In the arid to semi-arid regions, the Bowen ratio shows a clear positive correlation with the Drought Soil Index (DSI) and a negative correlation with the Normalized Difference Vegetation Index (NDVI), suggesting sensitivity to soil moisture conditions. In the sub-humid climate zone, vapor pressure deficit (VPD) is the dominant factor influencing the Bowen ratio. In the wet and dry transition zone, soil moisture, VPD, NDVI and land-air temperature difference all have a role to play.