Analytical Complementary Relationship Between Actual and Potential Evaporation Defined by Steady State Reference Surface Temperature

Wednesday, 16 December 2015
Poster Hall (Moscone South)
Dani Or, ETH Swiss Federal Institute of Technology Zurich, Zurich, Switzerland, Milad Aminzadeh, ETH Z├╝rich, Zurich, Switzerland and Michael L Roderick, Australian National University, Research School of Earth Sciences and Research School of Biology, Canberra, Australia
The definition of potential evaporation remains widely debated despite its centrality for hydrologic and climatic models. We employed an analytical pore-scale representation of evaporation from porous surfaces to define potential evaporation using a hypothetical steady-state reference temperature for air and evaporating surface. The feedback between drying land surfaces and overlaying air properties is implicitly incorporated in the hypothetical steady-state where the sensible heat flux vanishes and available energy is consumed by evaporation. Potential evaporation based on steady-state surface temperature was in surprisingly good agreement with class A pan evaporation measurements suggesting that pan evaporation occurs with negligible sensible heat flux. The model facilitates a new analytical generalization of the asymmetric complementary relationship across a wide range of meteorological conditions with good agreement between measured and predicted actual evaporation.