Wide-Area Estimates of Evapotranspiration by Red Gum (Eucalyptus camaldulensis) and Associated Vegetation in the Murray-Darling River Basin, Australia

2015 Spring Cyberseminar Series

Presenter(s):
Pamela Nagler / USGS Southwest Biological Science Center

Talk Description:

Wide-Area Estimates of Evapotranspiration by Red Gum (Eucalyptus camaldulensis) and Associated Vegetation in the Murray-Darling River Basin, Australia

Pamela L. Nagler (1), Tanya M. Doody (2), Edward P. Glenn (3), Christopher J. Jarchow (1), Armando Barreto-Muῆoz (4) and Kamel Didan (4)

1 US Geological Survey, Southwest Biological Science Center, Sonoran Desert Research Station, 1110 E. South Campus Drive, Room 123, Tucson, AZ 85721, USA

2 CSIRO Land and Water, Waite Road - Gate 4, Glen Osmond SA, Australia

3 Environmental Research Laboratory of the University of Arizona, 2601 E. Airport Dr., Tucson, AZ, 85706

4 Electrical and Computer Engineering, University of Arizona, Tucson, AZ, 85721

The purpose of this study was to characterize water use by the riparian tree, Red Gum (Eucalyptus camaldulensis), in the Lower Murray-Darling River basin of Australia, using a remote sensing algorithm developed to calculate evapotranspiration (ET) in U.S. riparian ecosystems. Sap flux was measured at 16 locations on the Murray and Murrumbidgee Rivers from August of 2005 to June of 2012.  These sap flux measurements were used to determine if the ground-based estimates of ET were correlated with the remotely-sensed predictive ET algorithm so that it could be used to estimate annual rates of water consumption by riparian vegetation over entire irrigation districts.  Remotely sensed ET data were parameterized using local meteorological station potential evapotranspiration (ETo) data (FAO56), rainfall from the Bureau of Meteorology and enhanced vegetation index (EVI) data from selected 250 m resolution pixels from the Moderate Resolution Imaging Spectrometer (MODIS). The MODIS ET algorithm accurately reproduced red gum sap flow ET measurements when the MODIS estimates were corrected for the fractional cover of red gums on the floodplain.  The ET algorithm was then applied to a 38,134 ha riparian area in the Yanga National Forest near the town of Balranald, New South Wales.  Flows into the forest from the Murrumbidge River had an annual mean of 1,004 million cubic meters (mcm) per year from 2000-2013, a drought period in the basin, while mean annual precipitation was 351 mm yr-1 over the same period. Mean ET estimated by MODIS imagery was 795 mm yr-1, of which an estimated 65% was from red gum and the remainder from understory grasses. The difference between total ET and precipitation (444 mm yr-1), projected over the area of red gum forest, was 169 mcm yr-1, presumably derived from groundwater. Thus, on this river reach about 17% of inflows were consumed by red gums and associated vegetation. This study supports ground sap flow studies suggesting that red gum trees are resilient to drought conditions and that floods at five year intervals appear to be sufficient to maintain healthy stands of trees and associated grasses.

CUAHSI's Spring 2015 Cyberseminar Series on  Evapotranspiration - Frontiers in measurement, modeling and management from the leaf to the landscape!

Hosted by Steven Brantley, Joseph W. Jones Ecological Research Center