Relationship between evapotranspiration and precipitation pulses in a semiarid rangeland estimated by moisture flux towers and MODIS vegetation indices

• Published in: Journal of arid environments Vol. 70; no. 3; pp. 443 - 462
• Main Authors: Nagler, P.L., Glenn, E.P., Kim, H., Emmerich, W., Scott, R.L., Huxman, T.E., Huete, A.R.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.08.2007; Elsevier
• Subjects: air temperature; Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; botanical composition; Ecohydrology; estimation; evapotranspiration; Fundamental and applied biological sciences. Psychology; General aspects. Techniques; Grassland; grasslands; mathematical models; moderate resolution imaging spectroradiometer; moisture flux towers; precipitation; rangelands; Remote sensing; Riparian; seasonal variation; Semiarid environments; semiarid zones; Shrubland; shrublands; soil water storage; solar radiation; Synecology; Teledetection and vegetation maps; temporal variation; Terrestrial ecosystems; vegetation; vegetation cover; watersheds; Arizona; USA, Arizona; Grassland; Ecohydrology; Shrubland; Riparian; Semiarid environments; Remote sensing; Arid environment; Precipitation; Semi arid zone; Evapotranspiration; Humidity; Vegetation; Rangeland; Environment; Shrubbery
• ISSN: 0140-1963; 1095-922X
• DOI: 10.1016/j.jaridenv.2006.12.026

We used moisture Bowen ratio flux tower data and the enhanced vegetation index (EVI) from the moderate resolution imaging spectrometer (MODIS) on the Terra satellite to measure and scale evapotranspiration (ET) over sparsely vegetated grassland and shrubland sites in a semiarid watershed in southeastern Arizona from 2000 to 2004. The grassland tower site had higher mean annual ET (336 mm yr −1) than the shrubland tower site (266 mm yr −1) ( P<0.001). ET measured at the individual tower sites was strongly correlated with EVI ( r=0.80–0.94). ET was moderately correlated with precipitation ( P), and only weakly correlated with net radiation or air temperature. The strong correlation between ET and EVI, as opposed to the moderate correlation with rainfall, suggests that transpiration ( T) is the dominant process controlling ET at these sites. ET could be adequately predicted from EVI and P across seasons and tower sites ( r 2 = 0.74 ) by a single multiple regression equation. The regression equation relating ET to EVI and P was used to scale ET over 25 km 2 areas of grassland and shrubland around each tower site. Over the study, ratios of T to ET ranged from 0.75 to 1.0. Winter rains stimulated spring ET, and a large rain event in fall, 2000, stimulated ET above T through the following year, indicating that winter rain stored in the soil profile can be an important component of the plants’ water budget during the warm season in this ecosystem. We conclude that remotely sensed vegetation indices can be used to scale ground measurements of ET over larger landscape units in semiarid ranglelands, and that the vegetation communities in this landscape effectively harvest the available precipitation over a period of years, even though precipitation patterns are variably seasonally and interannually.