Soil moisture model (2 layers)
This page details the TFN forcing transformation function named climateTransform_soilMoistureModels_2layer. It is identical to the one layer model climateTransform_soilModels but it has a second deeper soil store whereby the free-drainage from the upper store drains into the deeper store and the maximum ET from the deep store equal the PET minus the shallow store ET. Like the one layer soil model, the two layer and can be used to simulate land cover change. Below are the following sections explaining aspects of the model different or additional to the one layer model:
The soil moisture model can be used to simulate one soil moisture profile or two parallel soil moisture profiles, which each represent different land cover types and can be used to simulate land cover change. Below is a diagram illustrating the one profile model (left) and the two parallel profile model; at the bottom of which is an equation showing how a flux from the two parallel deep stores are aggregated to a single flux.
The single profile soil moisture model is defined by the following two ordinary differential equations (extention of Kavetski et al. 2006). The first equation is for the upper store and the second for the deeper store:
The equations contains two state variable and requires the input of two daily meteorological time series. For the two store model both stores are simulated using the above equation. The only difference between the non-tree and tree stores is that the soil moisture capacity of the two stores can differ because the soil moisture capacity of the tree store is defined by a separate parameters, SMSCtrees. The table below details each of the equation variables.