Accurate calculation of Land Surface Heat Flux Based on Soil Observations over the Tibetan Plateau

Abstract

The land surface heat flux is a crucial parameter that plays a significant role in the transformation and cycling of energy and matter between the atmospheric and land surface layers. This parameter serves as an essential input for various numerical models. Most land surface schemes deduce soil heat flux by amalgamating the heat conduction equation and residual method of energy balance. However, substantial discrepancies could be observed in soil heat flux simulations. These occurred among different Numerical Weather Prediction and offline Land Surface models, even though they were driven by the same atmospheric processes. The presence of discrepancies in models necessitated the accurate calculation of soil heat flux in order to reduce uncertainty in the allocation of sensible and latent heat flux at the surface. By reducing this uncertainty, we could decrease uncertainties in surface energy partitioning, achieved through diminishing the bias in simulated precipitation. However, in the Tibet plateau, soil heat flux observations were sparsely distributed, and the coverage period was different and limited, primarily used for model and remote sensing validation. There was a notable gap in research on the precise variations in soil heat flux in the Tibet plateau, particularly in studies employing sampled soil observations to accurately calculate soil heat flux. This study addressed these aforementioned deficiencies by focusing on soil attributes in the Tibet plateau to accurately calculate soil heat flux. In calculating soil heat flux precisely, factors like topography, land use, and vegetation type were considered. To ensure stability, representative soil cores were carefully observed and selected, obtaining samples through a layer-by-layer sampling approach. All sampling work had currently been completed. Utilizing comprehensive, synchronous, and continuous soil heat flux observations at the BJ site, in conjunction with long-term observational data and soil samples, we employed sampled soil attributes and soil heat flux plate observations to ascertain the requisite parameters for accurate soil heat flux calculation. These parameters, including the physical properties and porosity of soil profiles, enabled us to precisely determine the surface soil heat flux fluctuations at the BJ site. As a result of global warming, the Nagqu region had experienced elevated temperature, augmented precipitation, and amplified soil heat flux. In summary, accurately calculating soil heat flux is vitally important for allocating sensible and latent heat flux at the surface, which in turn diminishes uncertainty in the surface energy balance within models. This reduction in uncertainty is crucial for establishing a foundation to mitigate biases in local precipitation simulations within existing models.