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The energy required per unit mass of water vaporized. (J g −1) L v = Volumetric latent heat of vaporization. The energy required per unit volume of water vaporized. (L v = 2453 MJ m −3) E = Mass water evapotranspiration rate (g s −1 m −2) ET = Water volume evapotranspired (mm s −1) Δ = Rate of change of saturation specific humidity ...
Given the coarse accuracy of the Blaney–Criddle equation, it is recommended that it be used to calculate evapotranspiration for periods of one month or greater. [ 1 ] The equation calculates evapotranspiration for a 'reference crop', which is taken as actively growing green grass of 8–15 cm height.
The Penman equation describes evaporation (E) from an open water surface, and was developed by Howard Penman in 1948. Penman's equation requires daily mean temperature, wind speed, air pressure, and solar radiation to predict E. Simpler Hydrometeorological equations continue to be used where obtaining such data is impractical, to give comparable results within specific contexts, e.g. humid vs ...
Water stress is the most ubiquitous stress factor, often denoted as K w. Stress coefficients tend to be functions ranging between 0 and 1. The simplest are linear, but thresholds are appropriate for some toxicity responses. Crop coefficients can exceed 1 when the crop evapotranspiration exceeds that of RET.
Evapotranspiration is a combination of evaporation and transpiration, measured in order to better understand crop water requirements, irrigation scheduling, [4] and watershed management. [5] The two key components of evapotranspiration are: Evaporation: the movement
Monthly estimated potential evapotranspiration and measured pan evaporation for two locations in Hawaii, Hilo and Pahala. Potential evapotranspiration is usually measured indirectly, from other climatic factors, but also depends on the surface type, such as free water (for lakes and oceans), the soil type for bare soil, and also the density and diversity of vegetation.
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Field Water Efficiency (%) = (Water Transpired by Crop ÷ Water Applied to Field) x 100; Increased irrigation efficiency has a number of positive outcomes for the farmer, the community and the wider environment. Low application efficiency infers that the amount of water applied to the field is in excess of the crop or field requirements.