Measurement of evapotranspiration in phreatophyte areas, Smith Creek Valley and Carson Desert, west-central Nevada, 1983

Evaporation from bare soils and evapotranspiration from phreatophyte areas are major sources of natural groundwater loss in the Great Basin region of Nevada, Utah, and adjacent states. This study evaluated three methods for determining evapotrans- piration under natural conditions and provides quantitative estimates of evapotranspiration. Two of the methods used, the eddy-correlation and the Bowen ratio methods, measure actual evapotrans- piration under natural conditions, whereas the Penman method measures potential evapotranspiration. Phreatophytes at the Smith Creek Valley site (near Austin, Nev.) consist mainly of rabbitbrush. Actual evapotranspiration for 1983 at this site, estimated by the eddy-correlation method, was about 0.32 m/yr, compared with a calculated potential evapotrans- piration (measured by the Penman method) of about 2.0 m/yr. Phreatophytes at the Carson Desert site (near Fallon, Nev.) consist predominantly of greasewood. Estimated actual evapotranspiration at this site for 1983 (eddy-correlation method) was 0.18 m/yr, compared with a calculated potential evapotranspiration (Penman method) of 1.8 m/yr.