Project

evaporation; porous media; atmosphere coupling

Lead
Lay summary
Lay summary - )SoilEvapEvaporation from terrestrial surfaces - linking pore scale phenomena with landscape processes (   Brief Summary (About 40 words) Evaporation determines the amounts of water sent to the atmosphere and what is left for plants and life in soils. We address new fundamental aspects of evaporative water losses from porous surfaces that define landscape scale fluxes and drying dynamics.     Abstract (100-150 words) Evaporation rates and patterns affect energy balance of terrestrial surfaces and drive the hydrologic cycle. Evaporative losses define plant physiological function through transpiration, and affect available water for plants and microorganisms inhabiting the soil. Despite the importance of drying for many natural and engineering applications, predictions remain a challenge. The project addresses links between soil properties and evaporation dynamics upscaling fluxes from discrete pores as a surface progressively dries out to macroscopic evaporative losses from terrestrial surfaces. New and unaccounted-for phenomena such as the roles of surface topography and heterogeneity on enhanced evaporative losses would be considered at hydrologic scales. We will pursue a research strategy combining theoretical and modeling with field scale experiments.   Goal (50-70 words) The project would provide new information and upscaling schemes for bridging the gap between porous medium controls at laboratory and field scales and would broaden the physical basis for: (i) quantifying coupling between soil and atmosphere (mass and energy fluxes); (ii) accounting for processes controlling spatio-temporal patterns of evaporative losses (heterogeneity and topography); and (iii) developing physically-based boundary conditions for operational hydrologic and climatic large scale models.   Significance (50-100 words) As key component in the Earth’s hydrologic and energy balances, physically-based large scale parameterization are critical for developing predictive capabilities to link soil properties and conditions with future evaporative losses. These are not only important for present day land and water resource management, but also for future climate change scenarios in which soil surface interactions are known to play a critical role.

Direct link to Lay Summary

Last update: 21.02.2013

Active participation

Number	Title	Start	Funding scheme

Evaporation rates and patterns affect energy balance of terrestrial surfaces and drive the hydrologic cycle. Evaporative losses define plant physiological function through transpiration, and affect available water for plants and microorganisms inhabiting the soil. Notwithstanding the prominence of evaporative drying for many natural and engineering applications, prediction of drying rates from porous media remain a challenge due to interactions between energy and atmospheric conditions (radiation, humidity, temperature, air velocity) and porous medium properties often resulting in abrupt transitions and complex dynamics. The working hypothesis is that through proper integration of porous medium small-scale physical processes (elucidated in the previous SNSF project) affecting phase continuity, gradients and flows, and surface wetness dynamics, the prediction of evaporation patterns and fluxes at larger scales would be improved. Additionally, emergent and unaccounted-for phenomena such as surface topography and heterogeneity-enhanced evaporative losses would be considered at operational hydrologic scales. The objective is to quantify the role of porous media properties and processes in large scale evaporative losses using model-based upscaling schemes guided by experiments. We envision two primary lines of research supporting two PhD projects. One would focus on theory, laboratory and field experiments to quantify effects of soil textural heterogeneity that are hypothesized to enhance evaporative losses at field scale, and a related topic of evaporation from sloping surfaces to assess whether surface topography significantly affects evaporative losses (relative to flat surfaces). The other PhD student would focus on an important yet understudied role of surface wetness on rates of vapor transfer from wet pores across atmospheric viscous sub-layer (next to surface) using combination of modeling, wind tunnel experiments, and detailed field studies. Both PhD projects are ultimately aimed at upscaling and deriving parameterization schemes for hydrologic modeling at field scale. In collaboration with colleagues in Jülich we plan to combine dielectric (radar, radiometer, TDR) measurements of surface water content with thermal imagery at field scale to directly quantify evaporation rates from texturally heterogeneous soil surfaces under natural conditions. Results of this project are expected to provide data and upscaling schemes for bridging the gap between porous medium controls at laboratory and field scales and would provide the physical basis for: (i) quantifying coupling between soil and atmosphere (mass and energy fluxes); (ii) account for processes controlling spatio-temporal patterns of evaporative losses (heterogeneity and topography); and (iii) develop physically-based boundary conditions for operational hydrologic and climatic continuum models. Derivation of large scale parameterization with process-based boundary conditions linking soil with atmosphere and surface energy would be particularly important for models predicting processes under future climate change scenarios in which soil surface interactions are known to play a critical role.