For daily calculations, G (MJ m-2 day-1) can be estimated using a simplified approach to the heat balance of the soil profile:
where T is the mean daily air temperature (°C), T-1 is the mean air temperature (°C) of the preceding three-day period, and 0.1 is an empirical conversion factor (MJ m-2 day-1 °C-1). Because the magnitude of daily soil heat flux beneath densely planted grass is relatively small, it can be neglected (i.e., G = 0).
For monthly time-step calculations, G can be computed from the mean monthly temperatures of the current and preceding months as
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