Land-Surface Interactions with the Atmosphere Over the Iberian Semi-Arid Environment (LIAISE): Surface-Heterogeneity Observations and Modeling Framework

Heterogeneity is a key aspect in representing the land surface and its interaction with the atmospheric boundary layer. The nature of this heterogeneity varies with the length scale that is being considered, and as the resolution of models is increased, the method for representing this heterogeneity needs to be re-evaluated. The method commonly used in land surface models (LSM) to represent heterogeneity is the tile approach, whereby each surface can be considered as being in equilibrium with the atmosphere above it. However the assumptions used for both blending heights and surface turbulence using Monin-Obukhov and similarity theory make the tile approach invalid at high resolutions and alternative methods will need to be considered.

The scale of heterogeneity in land cover at the surface is largely a result of variations in the availability of soil moisture required for transpiration. As such, semi-arid environments have heterogeneous landscapes that are challenging for land surface models. With this in mind, the LIAISE (Land surface Interactions with the Atmosphere over the Iberian Semi-arid Environment) observational campaign has been designed to help improve our understanding of the drivers of heterogeneity and its response on the surface fluxes. The campaign brings together a period of ground based measurements with Special Observational Periods (SOP) that concentrate on observing the boundary layer structures. Details of the SOPs will be given in another presentation, whilst here we will concentrate on the longer term surface sites.

Details will presented on the extensive network of surface energy budget observations, which will cover differing land cover types as well as irrigated versus non-irrigated environments. Additional sites will also provide estimates of heterogeneity in soil moisture profiles that will complement the main energy balance sites along with scintollometers and remotely sensed soil moisture metrics as well as Land Surface Temperature (LST) from aircraft.

In addition to details about the observational plans, we will also describe a number of international modelling studies that will utilise these measurements in order to increase our understanding of the performance of land surface models in semi-arid environments and the representation of surface heterogeneity. The modelling will include studies on the transferability of the models within the heterogeneous landscape as well as the transition of surface fluxes through periods of soil moisture dry-down. Presenting the initial protocol for the modelling studies will enable the community to engage with the experiments and provide important feedback that can help to complete the experimental design.