Earth’s Green Blanket: A study of Heat Transfer through Grass

Land-atmosphere interactions play a key role in the Earth’s climate. The surface temperature is a key parameter in calculating the latent and sensible heat flux and thus important for the closure of the surface energy balance (SEB). Yet vegetated surfaces have different properties compared to bare soil and thus behave differently. Grass-vegetated surfaces are by far the most common type of land cover, covering over 40 % of all land area. Therefore, accurate modelling of soil and grass temperatures is essential for improving numerical weather prediction models.

In current weather models, the surface temperature is often estimated using an empirical skin resistance model, which may lead to significant errors in both the phase and amplitude of the surface temperature, negatively affecting the closure of the SEB. A more refined and physics-based approach is thus needed for accurate modelling of heat transfer processes in the vegetation-soil continuum.

In this research we investigate a new modelling approach for grass-vegetated and topsoil layers, using both analytical and numerical diffusive modelling approaches, building on the work of Van Dijk (2024), where grass was treated as a homogeneous sponge-layer with a uniform thermal diffusivity. The aim is to capture the temperature dynamics within the grass (and soil) layer and compare these with millimetre-resolution observations using distributed temperature sensing (DTS) measurements, as described in Ter Horst (2025).

Results indicate that a purely diffusive model is accurate in describing the temperature dynamics within the soil, but is not fully able to capture the heat transfer within the vegetation layer accurately. Therefore, adjustments are made to the vegetation ‘sponge’-layer, adding a more realistic height-dependent density and a height-dependent (radiative) source term. 

First results from a rudimentary analytic model already show promising results for temperature profiles in quasi-steady state, both during night- and daytime. Similar temperature profile shapes to the DTS measurements are achieved, that would not have been possible for a purely diffusive model.