PLSC204 Lecture Notes - Lecture 12: Pan Evaporation, Surface Runoff, Transpiration
23 Jan 2019
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Document Summary
86% evaporation and 78% of precipitation occurs in the ocean areas. Transpiration (t) = vapor losses from plant surfaces due to transpiration (related to productivity) Evaporation (e) = vapor losses from soil and plant surfaces (non-transpirational, e. g. interception water) Evapotranspiration (et) = e + t (what actually occurs) Potential et (pet) = maximum losses under optimum soil conditions. A class-a evaporation pan used to help estimate potential evapotranspiration (pet) Once a day water level determined in stilling well and measured amount of water is added to bring the level backup to original mark. Evaporation from pan integrates effects of relative humidity, temp, wind speed, and other climatic variables related to vapor pressure gradient. For dense vegetation, pet = 0. 65 x pan evaporation. Pet is not affected by soil water content/potential. Partitioning of liquid water losses (discharge) and vapor losses (evaporation and transpiration) in regions varying from low (arid) to high (humid) levels of annual precipitation.
