On the simulation of sensible heat flux over the Tibetan Plateau using different thermal roughness length parameterization schemes

Abstract

The surface sensible heat flux is a major component of the heat source over the Tibetan Plateau (TP), and it has experienced significant changes during the past three decades. The mechanism for how these changes occur remains a controversial issue. This study estimates the sensible heat flux and its trend during 1981–2010 using in situ data and the Noah-MP land surface model. Five newly implemented parameterization schemes and one Noah-MP-based scheme for the thermal roughness length (z0h) were evaluated against in situ measurements to show how these schemes influence the simulation of the sensible heat flux. The results show that the sensible heat flux is very sensitive to the z0h parameterization scheme. Although z0h is different from the momentum roughness length (z0m), a simple scheme that neglects the difference between them can result in reasonable daily variations of the sensible heat flux. The scheme proposed by Zeng and Dickinson (1998) (hereafter, Z98) performed well in terms of simulating the annual mean sensible heat flux. We analyzed the climatic features of the sensible heat fluxes that were simulated using the Z98 scheme. The results indicated that the inter-annual variations of the sensible heat flux in the western and central TP were larger than those in the eastern TP. The sensible heat flux over the TP exhibited a significant decreasing trend during 1981–2010. The weakening trends over the western and central TP were higher than those in the eastern TP, and the TP-averaged weakening trend was ~ 2.7 Wm−2 per decade. Different schemes show some uncertainties in annual mean sensible heat flux, but all the schemes result in a decreasing trend.