Evaporation from heterogeneous surfaces at the field-plot scale: effect of lateral heat and water fluxes in soil and atmosphere

• Applicant: Professor Dr. Jan Vanderborght
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management
• Term: from 2008 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 66234063

• Final Report Year: 2017

Final Report Abstract

We developed a closed loop inversion method to infer soil hydraulic parameters from L-band brightness temperatures. L-band brightness temperatures were monitored from three different plots with a different management leading to a different surface roughness and different soil structure. Besides soil hydraulic parameters, also roughness parameters could be retrieved from L-band measurements. The retrieved hydraulic parameters of the different plots were consistent with expected differences due to different soil management and the retrieved roughness parameters with parameters derived from laser scans. The retrieved hydraulic parameters were validated by comparing simulated and measured water contents and by comparing differences in simulated evaporation between different plots with measured differences in surface temperatures between the plots. The parameters or properties of the porous medium and its interface with the free flow which are most important for the transfer between the porous medium and the free flow over a larger time scale and under the climatic conditions in our experiments were the hydraulic properties of the field plots. However, parameterization of surface roughness and vapor transfer was found to be important for interpreting remote sensing data that depend strongly on the water content profiles close to the soil surface, such as micro-wave radar measurements. An exhaustive review of the theory behind different model concepts that are used to describe evaporation processes at the continuum scale was carried out in collaboration with SP2. This review confirmed that when transfer processes can be described as one-dimensional processes, i.e. when lateral gradients in state variables in the porous medium and the free flow can be neglected, the properties of the porous medium that determine the liquid flow are most important to describe evaporation losses from initially wet soils over a longer time period. However, diurnal dynamics of evaporation fluxes and water content and temperature profiles (also isotope concentration profiles) are strongly determined by the vapor transport and its parameterization in the porous medium. We showed that the shape of the water content profiles close to the soil surface has a characteristic S-shape during stage II evaporation. Methods like unilateral NMR and isotope profile measurements offer opportunities to determine these profiles and therefore infer the evaporation stage. For laterally heterogeneous porous media, we demonstrated that a coupled description of flow and transport processes in both the porous medium and the free flow is important and that approaches that neglect the effects of lateral gradients in either the free flow or the porous medium do not capture the effect of the heterogeneity on the fluxes.

Publications

• (2017). Heat and water transport in soils and across the soil-atmosphere interface – Part 1: Theory and different model concepts. Water Resources Research, accepted
  Vanderborght J., T. Fetzer, K. Mosthaf, K. Smits, R. Helmig
  
• (2012), New improved algorithm for sky calibration of L-band radiometers JÜLBARA and ELBARA II, 12th Specialist Meeting on Microwave Radiometry and Remote Sensing of the Environment (MicroRad), 2012 Frascati, Italy, 5-9 March 2012
  Dimitrov, M., K. G. Kostov, F. Jonard, K. Z. Jadoon, M. Schwank, L. Weihermüller, N. Hermes, J. Vanderborght, and H. Vereecken
  
• (2013), Effects of near surface soil moisture profiles during evaporation on far-field ground-penetrating radar data: A numerical study, Vadose Zone Journal, 12(2)
  Moghadas, D., K. Z. Jadoon, J. Vanderborght, S. Lambot, and H. Vereecken
  
• (2014), Estimation of the near surface soil water content during evaporation using air-launched ground-penetrating radar, Near Surface Geophysics, 12(5), 623
  Moghadas, D., K. Z. Jadoon, J. Vanderborght, S. Lambot, and H. Vereecken
  
• (2014), Soil hydraulic parameters and surface soil moisture of a tilled bare soil plot inversely derived from l-band brightness temperatures, Vadose Zone Journal, 13(1)
  Dimitrov, M., J. Vanderborght, K. G. Kostov, K. Z. Jadoon, L. Weihermüller, T. J. Jackson, R. Bindlish, Y. Pachepsky, M. Schwank, and H. Vereecken
  
• 2015), Soil hydraulic parameters of bare soil plots with different soil structure inversely derived from l-band brightness temperatures, Vadose Zone Journal, 14(8)
  Dimitrov, M., J. Vanderborght, K. G. Kostov, B. Debecker, P. S. Lammers, L. Damerow, and H. Vereecken