Nevada Water Science Center


Evapotranspiration Studies in Nevada

Contact Information

Mike Moreo
Hydrologist
Phone: (702) 564-4625
Email:

 

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

 

Nevada Water Science Center
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Upper Oasis Valley Middle

Site identification: 370249116424102

Study contact: Steve Reiner

ET Data

Annual ET reported (in inches): 19.6

Study period: 9/19/99 - 9/18/00

Days recorded: 650 from 12/09/98 to 9/18/00

 

Measurement method: Bowen ratio

Data: Download from NWISWeb

Graph of ET data

Location information

Latitude,
in decimal degrees
Longitude,
in decimal degrees
Altitude
37.0469444444 -116.711388889 3856

 

Photo of ET site

 

Photo of ET site

ET Source Area

Low-to-medium-density cover of 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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