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Topic: Evapotranspiration

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	Evapotranspiration - Wikipedia, the free encyclopedia
		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.
	en.wikipedia.org /wiki/Evapotranspiration (951 words)

	8(j) Actual and Potential Evapotranspiration
		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.
	www.physicalgeography.net /fundamentals/8j.html (275 words)

	Evapotranspiration
		During a drought, the significance of evapotranspiration is magnified, because evapotranspiration continues to deplete the limited remaining water supplies in lakes, streams and the soil.
		The average annual evapotranspiration for irrigated lands varies greatly and, apart from the climatic controls, is dependent on the grass or crop type, quantity of water applied, and length of the growing season.
		The estimated mean annual evapotranspiration for each State was determined from the mean annual statewide values of four principal components of the hydrologic budget-precipitation, surface-water inflow, surface-water outflow, and consumptive use.
	www.shodor.org /~jingersoll/igems/Teacher1b/evaplv1teach.html (2014 words)

	Evapotranspiration and Droughts
		Evapotranspiration is the water lost to the atmosphere by two processes-evaporation and transpiration.
		Minimum evapotranspiration rates generally occur during the coldest months of the year; maximum rates, which generally coincide with the summer season, when water may be in short supply, also depend on the availability of soil moisture and plant maturity.
		Changes in evapotranspiration during a drought depend largely on the availability of moisture at the onset of a drought and the severity and duration of a drought.
	geochange.er.usgs.gov /sw/changes/natural/et (2907 words)

	Evapotranspiration Systems
		Evapotranspiration (ET) is a method of onsite wastewater treatment and disposal that offers an alternative to conventional soil absorption systems for sites where protection of the surface water and groundwater is essential.
		Evapotranspiration is the net water loss caused by the evaporation of moisture from the soil surface and transpiration by vegetation.
		Evapotranspiration is also influenced by vegetation of the disposal field.
	www.cet.nau.edu /Projects/WDP/resources/treatmentsyst/Et.htm (1476 words)

	Evapotranspiration: An Operational Meteosat Application over Belgium
		In all cases, cloudy or clear, the contributions of the visible and the infrared parts of the spectrum to the incoming and the outgoing radiation at the surface are assessed, and the net surface radiation and the surface energy budget deduced.
		The evapotranspiration and the turbulent sensible and latent heat fluxes are first assessed at the level of a reference micro-meteorological station.
		This index is assumed to be representative for all of Belgium, the main factor governing the evapotranspiration being, for a temperate climate, the net radiation modulated by the presence or absence of clouds.
	www.wmo.ch /web/sat/en/ap6-14.htm (830 words)

	Crop evapotranspiration (BY M.I.T)
		Although the values for crop evapotranspiration and crop water requirement are identical, crop water requirement refers to the amount of water that needs to be supplied, while crop evapotranspiration refers to the amount of water that is lost through evapotranspiration.
		In non-weighing lysimeters the evapotranspiration for a given time period is determined by deducting the drainage water, collected at the bottom of the lysimeters, from the total water input.
		Evapotranspiration rates of the various crops are related to the evapotranspiration rate from the reference surface (ETo) by means of crop coefficients.
	hydrotechnic.150m.com /crop_water.html (7520 words)

	Evapotranspiration: Potential or Reference?
		In the reference evapotranspiration definition, the grass is specifically defined as the reference crop and this crop is assumed to be free of water stress and diseases.
		The reference evapotranspiration concept was introduced by irrigation engineers and researchers in the late 1970s and early 80s to avoid ambiguities that existed in the definition of potential evapotranspiration.
		It is recommended that the grass-reference evapotranspiration concept be used for irrigation scheduling and water management, hydrologic studies, and drainage researches in Florida in order to establish a common and standard ground between the growers/farmers and their advisors and between the researchers in Florida and other states.
	edis.ifas.ufl.edu /OUTLINE_AE256 (1300 words)

	EVAPOTRANSPIRATION
		Evapotranspiration information is needed by climate modellers; climatologists; vegetation ecologists and physiologists; ecosystem modellers; hydrological and water resource specialists; and regional planners.
		Evapotranspiration is the process responsible for the transfer of moisture from soil and vegetated surfaces to the atmosphere.
		Changes in evapotranspiration are likely to have large impacts on terrestrial vegetation, since the distribution and abundance of plant communities are controlled to a large extent by the quantity and seasonality of moisture.
	www.wmo.ch /web/gcos/terre/variable/evapot.html (740 words)

	Water Requirements of Florida Turfgrasses
		Evapotranspiration (ET) is a process by which water is transferred to the atmosphere from vegetative surfaces.
		Potential evapotranspiration (ETP) is defined as the water loss from a continuous surface of turf which fully shades the ground, exerts little or no resistance to the flow of water into the atmosphere, and always has an adequate supply of soil water (6, 2 I, 31).
		Under most circumstances actual evapotranspiration is less than potential evapotranspiration because one or more of the conditions in the definition restricts the flow of water into the atmosphere.
	edis.ifas.ufl.edu /EP024 (2474 words)

	[No title] (Site not responding. Last check: 2007-11-05)
		Evapotranspiration is combination two separate processes whereby water is lost on the one hand from the soil surface by evaporation and on the other hand from the crop by transpiration is refereed as evapotranspiration (ET).
		As mentioned earlier evapotranspiration is sum of the volume of water used by vegetation (transpiration) and that evaporated from soil (evaporation).
		Mehanna’s estimate of potential evapotranspiration was used to calculate Crop ET for 4 main crops of the Egypt at 9 meteorological stations using crop coefficient given in FAO paper.
	rajasthan.iwarp.com /photo3.html (3081 words)

	CIMIS - [ ET Overview ]
		Evapotranspiration (ET) is the loss of water to the atmosphere by the combined processes of evaporation (from soil and plant surfaces) and transpiration (from plant tissues).
		The logic behind the reference evapotranspiration idea is to set up weather stations on standardized reference surfaces for which most of the biophysical properties used in ET equations are known.
		Then, a crop factor, commonly known as crop coefficient (Kc), is used to calculate the actual evapotranspiration (ETc) for a specific crop in the same microclimate as the weather station site.
	wwwcimis.water.ca.gov /cimis/infoEtoOverview.jsp (924 words)

	Why Gaia Needs Rainforests
		Through evapotranspiration from the forest canopy, large amounts of rain-water are returned to the atmosphere, generating clouds that reflect sunlight back into the outer space, thus cooling the forested regions.
		Evapotranspiration over Amazonas involves enormous amounts of solar energy and, according to Brazilian climatologist, Luiz Carlos Molion, takes up as much as 80 per cent of the energy of sunlight directed down over the forests.
		With the Amazon forest totally destroyed, evapotranspiration is likely to fall to one half of its original value and precipitation down by as much as 20 per cent.
	www.i-sis.org.uk /LOG4.php (2362 words)

	Specifying Evapotranspiration Cycle (Site not responding. Last check: 2007-11-05)
		The cycle is composed of evapotranspiration periods of equal duration.
		Evapotranspiration parameters are defined at the beginning of each period, and are assumed to vary linearly from the beginning of one period to the beginning of the next period.
		Evapotranspiration periods are contained in a table in the Evapotranspiration Window.
	wwwbrr.cr.usgs.gov /projects/GW_Unsat/vs2di/hlp/solute/evapotranspirationCycle.html (153 words)

	The Water Cycle: Evapotranspiration, from USGS Water Science Basics
		In general, evapotranspiration is the sum of evaporation and transpiration.
		On this site, evapotranspiration is defined as the water lost to the atmosphere from the ground surface, evaporation from the capillary fringe of the groundwater table, and the transpiration of groundwater by plants whose roots tap the capillary fringe of the groundwater table.
		The transpiration aspect of evapotranspiration is essentially evaporation of water from plant leaves.
	ga.water.usgs.gov /edu/watercycleevapotranspiration.html (914 words)

	Evapotranspiration (Site not responding. Last check: 2007-11-05)
		Evaporation is the loss from open bodies of water, such as lakes and reservoirs, wetlands, bare soil, and snow cover; transpiration is the loss from living-plant surfaces.
		Assuming that moisture is available, evapotranspiration is dependent primarily on the solar energy, available to vaporize the water.
		Winds affect evapotranspiration by bringing heat energy into an area and removing the vaporized moisture.
	www.shodor.org /~igems/Student1b/evaplv1.html (1266 words)

	[No title]
		Evapotranspiration is the natural loss of water from soil, vegetation and open water surfaces and release as water vapor to the atmosphere.
		The accuracy of evapotranspiration estimates affects the accuracy of water demand predictions, water supply forecasts, and assessments of impacts of changes in land use and policies.
		The effect of changes in water level on evapotranspiration is captured in the calculation of the constant K. If the plants are completely submerged then the conductivity equals the conductivity of the open water surface, Kp, i.e transpiration does not contribute to the evapotranspiration of the area.
	www.cse.fau.edu /~maria/SFWMD/et.html (928 words)

	Journal of the American Water Resources Association: Evapotranspiration measurement and estimation of three wetland ... (Site not responding. Last check: 2007-11-05)
		ABSTRACT: Accurate estimates of evapotranspiration from areas dominated by wetland vegetation are needed in the water budget of the Upper St. Johns River Basin.
		By comparing computed evapotranspiration rates with those measured in the lysimeters, parameters in the Penman-Monteith, the Priestley-Taylor, and Reference-ET methods, and evaporation pan coefficients were estimated for monthly and seasonal cycles.
		This paper presents the measured evapotranspiration rates, evaporation pan coefficients, and the estimated parameter values for three different methods to compute evapotranspiration in the project area.
	www.findarticles.com /p/articles/mi_qa4038/is_200210/ai_n9090867 (438 words)

	8(i) Evaporation and Transpiration
		The process of evapotranspiration moves water vapor from ground or water surfaces to an adjacent shallow layer that is only a few centimeters thick.
		On a global scale, most of the evapotranspiration of water on the Earth's surface occurs in the subtropical oceans (Figures 8i-1 and 8i-2).
		Evapotranspiration generally exceeds precipitation on middle and high latitude landmass areas during the summer season.
	www.physicalgeography.net /fundamentals/8i.html (539 words)

	Reference.com/Encyclopedia/Evapotranspiration
		Potential evapotranspiration (PET) is the amount of water that could be evaporated and transpired if there was plenty of water available.
		Actual evapotranspiration is usually no greater than precipitation, with some buffer in time depending on the soils ability to hold water.
		An exception is areas with high water tables, where capillary rise can cause water from the groundwater to rise through the soil matrix to the surface.
	www.reference.com /browse/wiki/Evapotranspiration (360 words)

	MES Irrigation Scheduling
		Crop evapotranspiration is a fancy word for the consumptive use of water.
		Crop evapotranspiration is calculated using a weather station or an atmometer.
		The daily potato evapotranspiration amounts are the actual 1992 amounts at this arid location but the rainfall events are only hypothetical for instructional purposes.
	www.cropinfo.net /irrigschedule.htm (1702 words)

	Modeling Actual Evapotranspiration From Forested Watersheds Across the Southeastern United States
		As evapotranspiration is a major component in the forest water balances, accurately quantifying it is critical to predicting the effects of forest management and global change on water, sediment, and nutrient yield from forested watersheds.
		However, direct measurement of forest evapotranspiration on a large basin or a regional scale is not possible.
		The objectives of this study were to develop an empirical model to estimate long-term annual actual evapotranspiration (AET) for forested watersheds and to quantify spatial AET patterns across the southeast.
	www.srs.fs.usda.gov /pubs/viewpub.jsp?index=5605 (537 words)

	Chapter 1 - Introduction to evapotranspiration
		The evapotranspiration rate from a reference surface, not short of water, is called the reference crop evapotranspiration or reference evapotranspiration and is denoted as ET o
		The calculation of the reference crop evapotranspiration is discussed in Part A of this handbook (Box 1).
		Depending on the purpose of the calculation, the required accuracy, the available climatic data and the time step with which the calculations have to be executed, a distinction is made between two calculation methods.
	www.fao.org /docrep/X0490E/x0490e04.htm (3908 words)

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