植物学及园艺学英文boanyandhoriculure5.pptx

Evaporation, Transpiration,Sublimation Processes by which water changes phase- Liquid or solid to gas vapor Learning Objectives: Evapotranspiration (ET) Learn what conditions are necessary for evaporation to occur Learn what factors control evaporation rates Learn how to measure ET Learn where to find or how to compute variables needed to estimate ET Understand the difference between potential evapotranspiration (PET) and actual evapotranspiration (AET) Understand the difference between evaporation and transpiration Learn what factors control transpiration Become aware of common equations used to estimate ET Understand how ET varies in time and space Evaporation Phase change liquid to gas Hydrogen bonds broken – vapor diffuses from higher to lower vapor pressure At an open water surface, net evaporation = 0- bonds constantly forming and breaking Most takes place over open water surfaces such as lakes and oceans /karl/Unit2_Lecture1.ppt What controls evaporation? Energy inputs Temperature Humidity Wind Water availability What controls evaporation? Evaporation is energy intensive- latent heat of vaporization is 540 cal/gram Provided mainly by Solar energy - radiation Sensible heat – temperature –transferred via conduction and convection kinetic energy of water – internal energy, heat Energy that is absorbed during phase changes of water is not available to increase the surface temperature. Energy Budget net Net radiation: Rnet is determined by measuring incoming & outgoing short - & long-wave rad. over a surface. Rnet can – or + If R > 0 then can be allocated at a surface as follows: Rnet = (L)(E) + H + G + Ps L is latent heat of vaporization, E evaporation, H energy flux that heats the air or sensible heat, G is heat of conduction to ground and Ps is energy of photosynthesis. LE represents energy available for evaporating water Rnet is the primary source for ET & snow melt. /faresa/courses/nrem600/10-02%20Lecture.ppt In a watershed Rnet, (LE) latent heat and sensib