The magnitude of G varies greatly across different landscapes. Commonly used approaches to calculate LE and evapotranspiration (ET), such as the Penman-Monteith equation, the Priestley-Taylor equation, and the residual of the energy balance, not only need high-fidelity R NET but also require G to calculate the available energy. Ground heat flux accounts for the energy gained or lost during belowground warming or cooling. Net radiation, R NET, and G are balanced by latent heat ( LE), sensible heat ( H), and chemical energy provided by metabolism or used by photosynthesis in plants ( V), a negligible amount. Ground heat flux ( G) is an integral part of the surface energy budget ( R NET − G = LE + H + V). Results from this work have the potential to improve evapotranspiration estimates and guide appropriate G model selection and development for various land uses.
Global model mean midmorning instantaneous G is highest during September, October, and November at 63.42 (☑6.84) Wm −2, while over December, January, and February G is lowest at 53.86 (☑8.09) Wm −2 but shows greater intermodel uncertainty. We produce global decadal data sets of G to illustrate regional and seasonal sensitivities, as well as uncertainty. The instantaneous midday variability in G is best captured by models forced with net radiation, while models forced by temperature show the least error at both instantaneous and daily time scales. We provide the largest review of these methods to date ( N = 6), evaluating modeled G against measured G from 88 FLUXNET sites. There are a wide range of approaches to model G for large-scale applications, with a subsequent wide range of estimates and accuracies.
Algorithms that calculate LE and H require available energy, the difference between net radiation, R NET, and G. Uncertainty in ground heat flux ( G) means that evaluation of the other terms in the surface energy balance (e.g., latent and sensible heat fluxes ( LE and H)) remains problematic.
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