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Unformatted text preview: Basic defnitions: Evapotranspiration : all processes by which water in liquid phase at or near the earths surFace becomes atmospheric water vapor Evaporation usually describes direct vaporization oF water From open water surFaces and bare soil Transpiration is evaporation From within leaves oF vegetation Together these uxes reFerred to as evapotranspiration ( ET ) Notes: Estimating ET is important because (e.g.) : 1) long-term water balance (need P and E estimates) determines available water; 2) most Food supply grown using irrigated agriculture (eFfcient irrigation requires knowledge oF transpiration by crops); 3) ET rate during interstorm periods controls soil moisture evolution (impacts subsequent ooding); 4) ET couples the surFace water an energy budgets Direct measurement oF actual evapotranspiration is much more diFfcult (and expensive) than precip. or streamow Closest readily available (easy) measurement network are evaporation pans (only measure open water [potential] evaporation)...
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- Fall '10