Soil–Litter–Iso is a one-dimensional model for coupled transport of heat, water and stable isotopes (HDO and H218O) in soil and litter. It is sufficiently efficient for use at regional scale, yet includes the complexity of coupled heat and water transport enabling decomposition of the total moisture flux into liquid and vapour components. The numerical implementation is based on Ross’ fast solution to the Richards equation (Ross, 2003). This, combined with the explicit solution of the energy and moisture equations at the soil/air interface, permit the isotopic calculations to be performed with thick soil layers and large time steps, resulting in significantly improved computational efficiency compared with existing isotopically-enabled soil models of similar complexity.
Improvements to SLI since its original publication (Haverd and Cuntz, 2010), include modified soil water extraction; modified soil surface energy balance computation; and a new solution for the coupled heat and moisture equations under freezing conditions. These are described in Haverd et al. 2013.