HR: 1400h
AN: H33A-03    [Abstracts]
TI: Relationship Between Evapotranspiration and Precipitation Pulses in a Semiarid Rangeland Estimated by Moisture Flux Towers and MODIS Vegetation Indices
AU: * Nagler, P L
EM: pnagler@ag.arizona.edu
AF: University of Arizona, School of Natural Resources, 125 Biological Sciences East, Tucson, AZ 85721, United States
AU: Glenn, E P
EM: eglenn@ag.arizona.edu
AF: University of Arizona, Soil, Water and Environmental Science Dept., Environmental Research Laboratory, 2601 E. Airport Drive, Tucson, AZ 85706, United States
AU: Kim, H
EM: hjkim@ag.arizona.edu
AF: University of Arizona, Soil, Water and Environmental Science Dept., Terrestrial Biophysical and Remote Sensing Lab, #43 Shantz Bldg., Tucson, AZ 85719, United States
AU: Emmerich, W E
EM: bemmerich@tucson.ars.ag.gov
AF: USDA-Agricultural Research Service, Southwest Watershed Research Center, 2000 E. Allen Rd., Tucson, AZ 85719, United States
AU: Scott, R L
EM: rscott@tucson.ars.ag.gov
AF: USDA-Agricultural Research Service, Southwest Watershed Research Center, 2000 E. Allen Rd., Tucson, AZ 85719, United States
AU: Huxman, T E
EM: huxman@email.arizona.edu
AF: University of Arizona, Ecology and Evolutionary Biology, Harvill Bldg., Tucson, AZ 85719, United States
AU: Huete, A R
EM: ahuete@ag.arizona.edu
AF: University of Arizona, Soil, Water and Environmental Science Dept., Terrestrial Biophysical and Remote Sensing Lab, #43 Shantz Bldg., Tucson, AZ 85719, United States
AB: 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 near the Upper San Pedro River 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 (r2 = 0.74) by a single multiple regression equation. The regression equation relating ET to EVI and P was used to scale ET over 25 km2 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 rangelands, 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.
DE: 1218 Mass balance (0762, 1223, 1631, 1836, 1843, 3010, 3322, 4532)
DE: 1640 Remote sensing (1855)
DE: 1814 Energy budgets
DE: 1818 Evapotranspiration
DE: 1854 Precipitation (3354)
SC: Hydrology [H]
MN: 2007 Joint Assembly