Nevada Water Science Center

Evapotranspiration Studies in Nevada

Contact Information

Mike Moreo
Phone: (702) 564-4625


Mailing Address
Nevada Water Science Center
160 N. Stephanie St.
Henderson, NV 89074


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Middle Oasis Valley

Site identification: 370039116432402

Study contact: Steve Reiner

ET Data

Annual ET reported (in inches): 29.9

Study period: 1/09/98 - 1/09/00

Days recorded: 1012 from 4/25/97 to 1/31/00


Measurement method: Bowen ratio

Data: Download from NWISWeb

Graph of ET data

Location information

in decimal degrees
in decimal degrees
37.0108333333 -116.723333333 3691


Photo of ET site


Photo of ET site

ET Source Area

Low-to-medium-density cover of wire and saltgrass


Study Information

ET was quantified by identifying areas of ongoing ground-water ET, delineating unique areas of ET defined on the basis of similarities in vegetation and soil-moisture conditions (referred to as ET units), and computing ET rates for each of these ET units using micrometeorological data. Mean annual ET for each ET unit was calculated as the product of the unit's acreage and annual ET rate. Mean annual evapotranspiration from the Oasis Valley area was calculated as the sum of mean annual ET determined for each ET unit.

Eight ET units were delineated within Oasis Valley on the basis of spectral-reflectance characteri-stics derived from satellite imagery acquired in 1992. Together these ET units encompassed about 3,426 acres of sparse to densely vegetated grassland, shrubland, and wetland. About 35 percent of this acreage is sparse to moderately dense grassland (SGV) and 26 percent (892 acres) is sparse to moderately dense shrubland (SSV). Denser vegetation types, such as dense meadow and woodland vegetation (DMV), moderately dense to dense grassland vegetation (DGV), and dense wetland vegetation (DWV), make up about 35 percent of the total area. About 4 percent of the area is moist bare soil (MBS), submerged and sparse emergent aquatic vegetation (SAV), or open water body (OWB).

The Bowen-ratio method, based on balancing the energy budget, was used to compute ET rates at 5 sites within the 3 largest ET units in Oasis Valley. ET rates were computed from micrometeorological data collected from 1996 through 2000. Annual ET at these sites ranged from 3.14 ft over dense meadow vegetation to 0.62 ft over sparse shrubland vegetation. Differences in ET rates computed for sites within an ET unit are attributed to spatial changes in the density of local vegetation.

An annual ET rate for each of the eight ET units was estimated by averaging all ET rates calculated for sites located within the unit. Averages were determined from ET rates computed at 5 ET sites in Oasis Valley and 9 similar ET sites in nearby Ash Meadows. Average annual ET rates range from 1.2 ft/yr for SSV to 8.6 ft/yr for OWB and SAV.

An estimate of the mean annual ET from Oasis Valley was computed by summing estimates of the mean annual ET from each ET unit. Estimates of mean annual ET range from 8.6 acre-ft at OWB to 2,700 acre-ft at DMV. The estimate of the mean annual ET from Oasis Valley is 7,800 acre-ft.

Mean annual ground-water ET was calculated by removing water from the estimate of mean annual ET contributed by local precipitation. The local precipitation component was assumed to be equal to the mean, annual, long-term precipitation of 0.5 ft. Estimates of mean annual ground-water ET from each ET unit range from 8.1 acre-ft at OWB to 2,300 acre-ft at DMV. Mean annual ground-water ET from Oasis Valley is estimated at 6,000 acre-ft.


Study Publication: WRIR01-4239




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