What are the factors affecting evaporation?
What are the factors of evaporation and transpiration?
What are the methods of measuring actual evaporation and transpiration?
Change of mass or volume is often used. There are some clever ways too, including change in pH and/or electrical conductivity of a solution.
Howdy Abbas Kashani ,
There are articles here on RG that describe measurement methods that might help with modern methods of measurement. As to your first two questions, I offer a few comments here for your convenience from my Soil Moisture Review for WES (1985) since they address general awareness of the processes of evaporation and transpiration.
APPENDIX B: "Symon's (1867) has said that 'evaporation is the most desperate branch of the desperate science of meteorology.' While some progress has been made in the ensuing century, our understanding of evapotranspiration is still insufficient. The difficulties encountered in the treatment of evapotranspiration accrue, in part, from the fact that it is not simply a meteorological problem. There are distinct contributions to actual evapotranspiration from soil and plant physics as well. Basically, evapotranspiration may be viewed as a limited process, in the sense that the rate of water loss is limited by available energy and/or the rate of water movement to the ground surface and/or the rate of water movement through plants and/or the rate of vapor removal by the atmosphere. The virtual intractability of the problem of evapotranspiration derives from the complexity of each of these limiting processes and their interaction."
Page 16: "Evaporation and transpiration are primary depletion mechanisms for soil moisture and must be considered in any soil moisture prediction scheme. Evapotranspiration is basically a limited process, where the evapotranspiration rate is limited by the supply of energy for vaporization, by ventilation to remove water vapor, or by the water supply. (lfh note: Ancient Greek Natural Philosophers questioned whether the sun or the wind were more effective in evaporation.) It involves solar energy, atmospheric radiation, sensible heat from the atmosphere, near-surface winds, conduction of heat from the soil, moisture movement within the soil, plant transmission of water to leaves, root growth, and the the rate of evapotranspiration itself, as it exceeds the rate at which water can be supplied."
Page 17: "The most important concept with respect to evapotranspiration was put forth in the mid-1940's by Thornthwaite et al. (1944), namely, potential evapotranspiration. Potential evapotranspiration is that evapotranspiration rate that is not limited by moisture supply, but only by energy supply and ventilation. . . ."
"A second organizing concept of great importance was put forth by Van den Honert in 1948 and extended by Cowan (1965) , namely, to treat the flow of moisture from the soil to the atmosphere through a plant as a catenary process, i.e., limited by the flow through the portion of the path with highest resistance. . . ." (lfh note: Catenary is chain-like with links that can break.)
"An excellent discussion of three stages of drying of a soil is given in Heller (1968), while research reported by Idso et al. (1974) and Jackson et al. (1973) describes surface color variations and soil moisture measurements related to drying of an irrigated soil."
Page 18: "In all the concepts of potential evapotranspiration , catenary processes for water movement through plants , and stages of drying of a soil have aided understanding of the complex process of evapotranspiration. Most soil moisture prediction models include these concepts and their mathematical implementation to some degree at present." (That was in 1985.)
Happy Trails, Len
Leonard Hall
Hello, dear Professor Basar, I am very happy and excited for your answer, thank you very much. Abbas Kashani
Howdy Abbas Kashani,
Thank you for your reply! I worry at times whether I help anyone. I am very pleased to read of your joy and excitement.
Happy Trails, Len
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