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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 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.
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 ...
Given the limited data input to the equation, the calculated evapotranspiration should be regarded as only broadly accurate. Rather than a precise measure of evapotranspiration, the output of the equation is better thought of as providing an order of magnitude. [2] The inaccuracy of the equation is exacerbated by extreme variants of weather.
The Penman-Monteith equation approximates net evapotranspiration (ET) from meteorological data as a replacement for direct measurement of evapotranspiration. The equation is widely used, and was derived by the United Nations Food and Agriculture Organization for modeling reference evapotranspiration ET 0 .
At least three times as much precipitation in the wettest month of winter as in the driest month of summer, and the driest month of summer receives less than 30 mm (1.2 in). Dsd = Mediterranean-influenced extremely cold subarctic climate; coldest month averaging below −38 °C (−36.4 °F) and 1–3 months averaging above 10 °C (50 °F).