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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.
Evapotranspiration can never be greater than potential evapotranspiration, but can be lower if there is not enough water to be evaporated or plants are unable to transpire maturely and readily. Some US states utilize a full cover alfalfa reference crop that is 0.5 m (1.6 ft) in height, rather than the general short green grass reference, due to ...
Potential evapotranspiration (PET), is the evaporation and transpiration that potentially could occur if a field of the crop had an ideal unlimited water supply. RET is the reference ET often denoted as ET 0 .
s2 (Large summer surplus) : Ih ≥ 33.3 and the surplus in the summer is larger than in the winter; w2 (Large winter surplus) : Ih ≥ 33.3 and the surplus in the winter is larger than in the summer; The deficiency of water in the soil is calculated as the difference between the potential evapotranspiration and the actual evapotranspiration. [2]
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 ...
Drier surroundings give a steeper water potential gradient, and so increase the rate of transpiration. Wind: In still air, water lost due to transpiration can accumulate in the form of vapor close to the leaf surface. This will reduce the rate of water loss, as the water potential gradient from inside to outside of the leaf is then slightly less.
Potential evapotranspiration (PET) is the amount of water that would be evaporated and transpired if there were enough water available. Higher temperatures result in higher PET. [ 5 ] Evapotranspiration (ET) is the raw sum of evaporation and plant transpiration from the Earth's land surface to atmosphere.
Inputs to SPEI datasets can include high-resolution potential evapotranspiration (PET) from the Global Land Evaporation Amsterdam Model (GLEAM) and hourly Potential Evapotranspiration (hPET). GLEAM is a set of algorithms designed to calculate actual evaporation, PET, evaporative stress, and root-zone soil moisture.