Catchments as Organised Systems

[C] Understanding and characterizing land surface-atmosphere exchange and feedbacks

The partitioning of incoming net radiation at the land surface between sensible and latent heat (evaporation) fluxes heavily influences local to regional climate and dynamics of the water cycle. The aim of this project is the assessment of evapotranspiration, a key driver of and a link between the Earth’s water cycle and land surface energy balance, at different scales.

The project uses three different and complementary approaches to quantify local to regional evapotranspiration and surface energy balance partitioning. The first approach uses the semi-physical-, Penman-Monteith equation combined with the complementary relationship and thermal remote sensing to derive high resolution estimates of evapotranspiration (group C-1, LIST). The second approach uses hydro-meteorological simulations with the WRF-NOAHMP-HYDRO model down to resolutions of 100 m to study the effects of soil-vegetation-atmosphere feedbacks and large turbulent eddy circulations on regional evapotranspiration with unprecedented detail. Additional assessments of the volumetric land-atmosphere water budget over time allows us to examine major processes and constraints associated with the evolution of the boundary layer under varying climate regimes. The third approach uses the thermodynamic limit on convective exchange to infer the magnitude of soil-vegetation-atmosphere interactions, atmospheric mixing processes, and local to regional evapotranspiration patterns (group C-3, MPI-BGC Jena). A dedicated field campaign performing micrometeorological measurements of the surface energy balance and the CAOS field observations will be used to evaluate these methods. These approaches are evaluated in a joint synthesis activity regarding surface energy balance estimates from local to catchment scale and their closure assumptions. The synthesis of these three approaches of vastly different complexity has the potential to substantially advance our ability to understand and robustly predict regional evapotranspiration and the surface energy balance.


Fig 1. Scintillometer (E. Thiem). A scintillometer measures atmospheric turbulence. The attenuation of an infrared light beam is a measure of turbulence strength which in turn relates to the exchange of temperature and humidity between the land surface and the atmosphere.


Fig 2. Unmanned aerial vehicle (UAV) with thermal infrared camera (C. Brenner). The amount of infrared radiation emitted by a surface depends on its temperature. Based on this principle, thermal infrared cameras measure land surface temperature, which is a key state variable in the estimation of surface energy fluxes. A thermal infrared camera mounted on an UAV allows land surface temperature to be assessed with high spatial and temporal scale.