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Encyclopedia > Evapotranspiration

Evapotranspiration (ET) is the sum of evaporation and plant transpiration. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and waterbodies. Transpiration accounts for the movement of water within a plant and the subsequent loss of water as vapour through stomata in its leaves. Evapotranspiration plays an important role in the water cycle. Evaporation is the process whereby atoms or molecules in a liquid state (or solid state if the substance sublimes) gain sufficient energy to enter the gaseous state. ... Divisions Land plants (embryophytes) Non-vascular plants (bryophytes) Marchantiophyta - liverworts Anthocerotophyta - hornworts Bryophyta - mosses Vascular plants (tracheophytes) Lycopodiophyta - clubmosses Equisetophyta - horsetails Pteridophyta - true ferns Psilotophyta - whisk ferns Ophioglossophyta - adderstongues Seed plants (spermatophytes) â€ Pteridospermatophyta - seed ferns Pinophyta - conifers Cycadophyta - cycads Ginkgophyta - ginkgo Gnetophyta - gnetae Magnoliophyta - flowering plants Adiantum pedatum (a fern... Transpiration is a continuous process caused by the evaporation of water from leaves of plants and its corresponding uptake from roots in the soil. ... Soil is material capable of supporting plant life. ... Interception, or canopy interception, is when precipitation does not reach the soil, and is intercepted by some vegetation. ... A body of water is any significant natural pool of water such as an ocean, a lake, or a river, covering the Earth or another planet. ... Divisions Land plants (embryophytes) Non-vascular plants (bryophytes) Marchantiophyta - liverworts Anthocerotophyta - hornworts Bryophyta - mosses Vascular plants (tracheophytes) Lycopodiophyta - clubmosses Equisetophyta - horsetails Pteridophyta - true ferns Psilotophyta - whisk ferns Ophioglossophyta - adderstongues Seed plants (spermatophytes) â€ Pteridospermatophyta - seed ferns Pinophyta - conifers Cycadophyta - cycads Ginkgophyta - ginkgo Gnetophyta - gnetae Magnoliophyta - flowering plants Adiantum pedatum (a fern... This is not about surgically created bowel openings; see stoma (medicine) In botany, a stoma (also stomate; plural stomata) is a tiny opening or pore, found mostly on the undersurface of a plant leaf, and used for gas exchange. ... In botany, a leaf is an above-ground plant organ specialized for photosynthesis. ... The movement of water around, over, and through the Earth is called the water cycle. ...

Potential evapotranspiration (PET) is a representation of the environmental demand for evapotranspiration. It is a reflection of the energy available to evaporate water, and of the wind available to transport the water vapour from the ground up into the lower atmosphere. Evapotranspiration is said to equal potential evapotranspiration when there is ample water. Wind is the roughly horizontal movement of air (as opposed to an air current) caused by uneven heating of the Earths surface. ... Saturns atmosphere is made up of hydorgen, helium and methane ...

## Evapotranspiration and the water cycle GA_googleFillSlot("encyclopedia_square");

Evapotranspiration is a significant water loss from a watershed. Types of vegetation and land use significantly effect evapotranspiration, and therefore the amount of water leaving a watershed. Because water transpired through leaves comes from the roots, plants with deep reaching roots can more constantly transpire water. Thus herbaceous plants transpire less than woody plants because herbaceous plants lack a deep taproot. Also, woody plants keep their structure over long winters while herbaceous plants must grow up from seed in the spring in seasonal climates, and will contribute almost nothing to evapotranspiration in the spring. Conifer forests tend to have much higher rates of evapotranspiration than deciduous forests. This is because their needles give them superior surface area, resulting in more pores for transpiration, and allowing for more droplets of rain to be suspended in and around the needles and branches, where the some of the droplets can then be evaporated. Factors that affect evapotranspiration include the plant's growth stage or level of maturity, percentage of soil cover, solar radiation, humidity, temperature, and wind. This article is about the plants used in cooking and medicine. ... Young castor oil plant showing its prominent two embryonic leaves (cotyledons), that differ from the adult leaves Dicotyledons or dicots is a name for a group of flowering plants whose seed typically contains two embryonic leaves or cotyledons. ... Orders & Families Cordaitales † Pinales   Pinaceae - Pine family   Araucariaceae - Araucaria family   Podocarpaceae - Yellow-wood family   Sciadopityaceae - Umbrella-pine family   Cupressaceae - Cypress family   Cephalotaxaceae - Plum-yew family   Taxaceae - Yew family Vojnovskyales † Voltziales † The conifers, division Pinophyta, are one of 13 or 14 division level taxa within the Kingdom Plantae. ... Deciduous means temporary or tending to fall off (deriving from the Latin word decidere, to fall off). ... Solar irradiance spectrum at top of atmosphere. ... Humidity is the concentration of water vapor in the air. ... Temperature is the physical property of a system which underlies the common notions of hot and cold; the material with the higher temperature is said to be hotter. ... Wind is the roughly horizontal movement of air (as opposed to an air current) caused by uneven heating of the Earths surface. ...

Through evapotranspiration, forests reduce water yield, except for in unique ecosystems called cloud forests. Trees in cloud forests condense fog or low clouds into liquid water on their surface, which drips down to the ground. These trees still contribute to evapotranspiration, but often condense more water than they evaporate or transpire. A cloud forest is a tropical or subtropical montane forest characterized by a high incidence of low-level cloud cover, usually at the canopy level, promoting development of an abundance of vascular epiphytes. ...

In areas that are not irrigated, actual evapotranspiration is usually no greater than precipitation, with some buffer in time depending on the soil's ability to hold water. It will usually be less because some water will be lost due to percolation or surface runoff. An exception is areas with high water tables, where capillary action can cause water from the groundwater to rise through the soil matrix to the surface. If potential evapotranspiration is greater than actual precipitation, then soil will dry out, unless irrigation is used. In chemistry and other physical sciences, percolation is a type of filtering. ... The water table is the upper limit of abundant groundwater. ... Capillary action or capillarity (also known as capillary motion) is the ability of a narrow tube to draw a liquid upwards against the force of gravity. ... High-altitude aerial view of irrigation in the Heart of the Sahara Irrigation (in agriculture) is the replacement or supplementation of rainfall with water from another source in order to grow crops. ...

Evapotranspiration can never be greater than PET, but can be lower if there is not enough water to be evaporated or plants are unable to readily transpire.

## Estimating evapotranspiration

Evapotranspiration cannot be measured directly. Pan evaporation data can be used to estimate lake evaporation, but transpiration and evaporation of intercepted rain on vegetation are unknown. There are two general approaches to estimate evapotranspiration indirectly.

### Catchment water balance

Evapotranspiration may be estimated by creating an equation of the water balance of a catchment (or watershed). The equation balances the change in water stored within the basin (S) with inputs and exports:

$Delta S = P - ET - Q - D ,!$

The input is precipitation (P), and the exports are evapotranspiration (which is to be estimated), streamflow (Q), and groundwater recharge (D). If the change in storage, precipitation, streamflow, and groundwater recharge are all estimated, the missing flux, ET, can be estimated by rearranging the above equation as follows:

$ET = P -Delta S - Q - D ,!$

### Hydrometeorological equations

The most general and widely used equation for calculating ET is the Penman equation. The Penman-Monteith variation is recommended by the Food and Agriculture Organization. The simpler Blaney-Criddle equation was popular in the Western United States for many years but it is not as accurate in regions with higher humidities. Other solutions used includes Makkink, which is simple but must be calibrated to a specific location, and Hargreaves. The Penman equation describes evaporation (E) from an open water surface. ... FAO emblem With its headquarters in Rome, the Food and Agriculture Organization (FAO) is a specialized agency of the United Nations that works to raise levels of nutrition and standards of living; to improve the production, processing, marketing, and distribution of food and agricultural products; to promote rural development; and...

## Potential evapotranspiration

Monthly estimated potential evapotranspiration and measured pan evaporation for two locations in Hawaii, Hilo and Pahala.

Potential evapotranspiration (PET) is the amount of water that could be evaporated and transpired if there was sufficient water available. This demand incorporates the energy available for evaporation and the ability of the lower atmosphere to transport evaporated moisture away from the land surface. PET is higher in the summer, on less cloudy days, and closer to the equator, because of the higher levels of solar radiation that provides the energy for evaporation. PET is also higher on windy days because the evaporated moisture can be quickly moved from the ground of plants, allowing more evaporation to fill its place. Image File history File links Potential_evapotranspiration_Hawaii. ... Image File history File links Potential_evapotranspiration_Hawaii. ... Official language(s) Hawaiian and English Capital Honolulu Largest city Honolulu Area  - Total  - Width  - Length  - % water  - Latitude  - Longitude Ranked 43rd 28,337 kmÂ² n/a km 2,450 km 41. ... A girl in a swimming pool Water (from the Old English waeter; c. ...

PET is expressed in terms of a depth of water, and can be graphed during the year (see figure). There is usually a pronounced peak in summer, which results from higher temperatures. For other senses of this word, see summer (disambiguation). ...

Potential evapotranspiration is usually measured indirectly, from other climatic factors, but also depends on the surface type, such free water (for lakes and oceans), the soil type for bare soil, and the vegetation. Often a value for the potential evapotranspiration is calculated at a nearby climate station on a reference surface, conventionally short grass. This value is called the reference evapotranspiration, and can be converted to a potential evapotranspiration by multiplying with a surface coefficient. In agriculture, this is called a crop coefficient. The difference between potential evapotranspiration and precipitation is used in irrigation scheduling. A lake is a body of water surrounded by land. ... [[Image:http://www. ... Soil is material capable of supporting plant life. ... Vegetation is a general term for the plant life of a region; it refers to the ground cover provided by plants, and is, by far, the most abundant biotic element of the biosphere. ... Irrigation scheduling is the process used by irrigation system managers to determine the correct frequency and duration of watering. ...

Average annual PET is often compared to average annual precipitation, P. The ratio of the two, P/PET, is the aridity index. Aridity index, AI, is a measure of the dryness of a climate. ...

Results from FactBites:

 Evapotranspiration - Wikipedia, the free encyclopedia (951 words) Evapotranspiration (ET) is the sum of evaporation and plant transpiration. Evapotranspiration may be estimated by creating an equation of the water balance of a catchment (or watershed). Potential evapotranspiration is usually measured indirectly, from other climatic factors, but also depends on the surface type, such free water (for lakes and oceans), the soil type for bare soil, and the vegetation.
 8(j) Actual and Potential Evapotranspiration (275 words) Potential evapotranspiration or PE is a measure of the ability of the atmosphere to remove water from the surface through the processes of evaporation and transpiration assuming no control on water supply. Actual evapotranspiration or AE is the quantity of water that is actually removed from a surface due to the processes of evaporation and transpiration. The rate of evapotranspiration is associated to the gradient of vapor pressure between the ground surface and the layer of atmosphere receiving the evaporated water.
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