FOR 1083: Multi-Scale Interfaces in Unsaturated Soil (MUSIS)

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Water distribution and dynamics within the unsaturated zone determine energy balance and key mass fluxes at the land-atmosphere interface at scales ranging from soil profile to continental response. Soil water redistribution and exchanges such as infiltration and evaporation at the interface with the atmospheric boundary layer above, or drainage and recharge with groundwater below often involve displacement of fluid fronts across soil layers and through heterogeneous boundaries. Current modelling concepts are inadequate for describing such complex displacement processes through naturally-heterogeneous soils with highly non-linear flow mechanisms involved, thus limiting their predictive capabilities simply because water-air interfaces may form a stable displacement front or may split into fingers and preferential flow domains, leading to vastly different patterns of water distribution and associated transport pathways. The central working hypothesis is that small-scale physics of moving water-air interfaces within heterogeneous soil structures and interplay among competing driving forces give rise to a wide array of macroscopic patterns of water and gas dynamics not captured by standard continuum models. The primary objective of this Research Unit is to characterise and quantify characteristic patterns of water and gas distributions as a function of