Evapotranspiration of mixed shrub communities in phreatophytic zones of the Great Basin region of Nevada (USA)

In this study, evapotranspiration (ET) was estimated for three valleys (White River, Spring Valley and Snake Valley) in the Great Basin region of Nevada (USA) during a 3-year period. ET estimates were based on an energy balance approach using the eddy covariance (EC) method and were scaled to the basin level by developing empirical relationships between ET and remotely sensed spectral data (Landsat). Annual EC–ET values for the three basins and previously published values attained for the same valleys during the same time period were correlated to average normalized difference vegetation index (NDVI) values for the growing period. Resulting empirical relationships accounted for 97% (p < 0·001) of the variation in the EC–ET estimate for the 10 May–5 September growing period, and 93% (p < 0·001) of the variation in the EC–ET estimates based on measured or projected yearly ET totals. Variations in yearly ET estimates at the different shrubland sites ranged from 20 to 50 cm during the two dry years (2006 and 2007, not including the irrigated site). Winter precipitation was shown to be a significant driving force in the physiological response of the plants and the yearly ET totals. In the case of White River Valley, the ratio of winter precipitation to reference evapotranspiration (ETref) declined from 79 to 11% over the 3-year monitoring period. Overall, ET rates in 2007 (May–Sept.) were highly correlated with the percentage cover of greasewood at the monitoring sites (R2 = 0·96***), regardless of the depth to groundwater. Copyright © 2010 John Wiley & Sons, Ltd.