Water Resources Professional Project Reports

Title

Remotely-measured Evapotranspiration of a Restoration Landscape at Bosque del Apache NWR

Document Type

Technical Report

Publication Date

7-2017

Abstract

Measuring riparian evapotranspiration (ET) has been a concern of water managers since the mid-20th century. Several methods have been used to measure ET, including lysimeters, sap flow sensors, and eddy covariance flux towers. More recently, satellite based ET modeling techniques have been developed for use over larger study areas. This professional project utilized the remote-sensing energy balance model known as METRIC (Mapping Evapotranspiration with High Resolution and Internalized Calibration) and focused on the managed portion of the Rio Grande floodplain of Bosque del Apache National Wildlife Refuge located in New Mexico. The METRIC model estimated ET before and after the clearance of 7.3 km2 (1805 acres) of invasive tamarisk forest and restoration to native bosque forest. ET estimations from 1999 and 2001 (pretamarisk removal) were compared to ET estimations from 2011 and 2013 (post-tamarisk removal) in an attempt to estimate potential ET changes. ET estimations from 2011 and 2013 were further compared between areas intensively managed and irrigated by the refuge and those with little post-tamarisk removal treatments and no irrigation. ET estimations from 1999, 2001, and 2011 were compared to the University of New Mexico eddy covariance flux tower located near the study area. Comparison of METRIC ET estimations to the University of New Mexico eddy covariance flux tower ET values showed a poor correlation (r2 = 0.51), giving low confidence to the METRIC model ET estimations. Results showed a qualitative reduction in pre-monsoon ET following tamarisk removal, and a higher ET value for post-treatment (2011 and 2013) lands with management compared to those with no management. Because quantitative estimations by the METRIC model are hampered by potential error, these results are called into question. Attempting to isolate the observed ET reduction to tamarisk removal by systematically eliminating outside factors was inconclusive because of large sources of potential error within the model. Overall, this investigation demonstrated the great complexity in measuring riparian ET and the limitations of applying the METRIC model to this particular environmental setting.

Language (ISO)

English

Keywords

riparian evapotranspiration, ET, lysimeters, sap flow sensors, eddy covariance flux towers, METRIC, Mapping Evapotranspiration with High Resolution and Internalized Calibration, Rio Grande, Bosque del Apache National Wildlife Refuge

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