Groeneveld (2008) Remotely-sensed groundwater evapotranspiration from alkali scrub affected by declining water table

Identification

• Journal: Journal of Hydrology
• Year: 2008
• Date: 2008-06-15
• Authors: David P. Groeneveld
• DOI: 10.1016/j.jhydrol.2008.06.011

Research Groups

• HydroBio, Advanced Remote Sensing, Santa Fe, NM, USA

Short Summary

This study evaluated the ability of remotely-sensed NDVI* to predict annual evapotranspiration (ET) and groundwater evapotranspiration (ETg) of alkali scrub over a 17-year period with a 2.5 meter water table decline. It found that NDVI* underestimated ETg due to its insensitivity to direct soil-surface evaporation of groundwater (Eg), and developed mathematical curves to estimate ETg based on depth to groundwater (DTW).

Objective

• To evaluate the effectiveness of remotely-sensed NDVI* for predicting annual total evapotranspiration (ET) and its groundwater component (ETg) in alkali scrub vegetation, particularly under conditions of declining water tables.
• To develop mathematical curves that estimate ETg based on depth to groundwater (DTW) for use in dynamic groundwater modeling applications.

Study Configuration

• Spatial Scale: San Luis Valley, Colorado, USA.
• Temporal Scale: A 17-year period, with annual data derived from mid-summer Landsat TM scenes.

Methodology and Data

• Models used: NDVI* (atmospherically-resistant normalized difference vegetation index), ET0 (grass reference evapotranspiration), logarithmic curve fitting. ETg was estimated by subtracting annual total precipitation from annual total ET estimates.
• Data sources: Mid-summer Landsat TM satellite data, micrometeorologic measurements (for comparison), depth-to-groundwater (DTW) measurements.

Main Results

• The study site experienced a 2.5 meter decline in depth to groundwater (DTW) over the 17-year period, accompanied by known declines in vegetation cover and ET.
• Remotely-sensed NDVI* underestimated groundwater evapotranspiration (ETg) when compared to micrometeorologic measurements.
• This underestimation was attributed to NDVI*'s insensitivity to the component of direct soil-surface evaporation of groundwater (Eg).
• Logarithmic curves were fitted to the ETg and DTW data sets, and the difference between these curves provided an estimate of Eg that approximated published values.
• Mathematical curves were developed to estimate ETg based on DTW, suitable for dynamic groundwater modeling applications for alkali scrub.

Contributions

• Provides novel mathematical curves for estimating groundwater evapotranspiration (ETg) as a function of depth to groundwater (DTW) specifically for alkali scrub, which are applicable in dynamic groundwater modeling.
• Highlights a critical limitation of using vegetation indices like NDVI* for estimating total ETg, by demonstrating its insensitivity to the direct soil-surface evaporation component (Eg).

Funding

• Not explicitly mentioned in the provided text.

Citation

@article{Groeneveld2008Remotelysensed,
  author = {Groeneveld, David P.},
  title = {Remotely-sensed groundwater evapotranspiration from alkali scrub affected by declining water table},
  journal = {Journal of Hydrology},
  year = {2008},
  doi = {10.1016/j.jhydrol.2008.06.011},
  url = {https://doi.org/10.1016/j.jhydrol.2008.06.011}
}