Colorado River Basin Focus Area Study: Evapotranspiration

Science Center Objects

New USGS-developed, remote-sensing based approaches were used to quantify agricultural irrigation water consumption on a field-by-field scale. The work produced the first ever Colorado River Basin-wide, 100-m scale actual ET estimate (2010) using Landsat imagery.

National Water Census  •  Colorado River Basin  •  Evapotranspiration  •  Snowpack  •  Water Use   •   Groundwater Discharge 

 

Evapotranspiration (ET)—the combination of water transpired from plants and water that evaporates from soil or open water bodies—is an important component of the CRB water budget. The USGS National Water Census program has advanced new methods of remote-sensing-based actual ET (ETa) estimation through the development of the Operational Simplified Surface Energy Balance (SSEBop) model (Senay and others, 2013).

The SSEBop ETa model uses land surface temperature (LST) derived from satellite imagery and integrates these data with local weather datasets (for example, net radiation, air temperature, humidity, wind speed, and air pressure) to produce estimates of ETa at the time of each satellite overpass. Time periods between satellite overpasses are interpolated using potential ET data derived from the land-based weather datasets.

Example of SSEBop Eta product: WAUSP: water census colorado focus area study

Example of SSEBop Eta product: Spatial distribution of (A ) annual evapotranspiration (millimeters per year) and (B ) evapotranspiration (millimeters per day) on the day of satellite overpass (July 6, 2013) in a selected part of the southern Willcox irrigation district in Arizona. Modified from G.B. Senay, USGS, written commun., Oct. 26, 2015. [ETa, actual evapotranspiration; mm, millimeter]

Evapotranspiration (ET) mapping at the Landsat spatial resolution (100 m) is essential to fully understand water use and water availability at the field scale. Water use estimates derived in the CRB FAS will be helpful to water planners and managers. These estimates also provide valuable input to water supply prediction models and water-resource management decision support systems.

Key Findings and Results

  • First ever basin-wide, 100-m scale ETa estimate was completed for 2010 using Landsat 5 and 7 imagery. 
  • 528 Landsat 8 images were used to estimate wall-to-wall ET in the Colorado River Basin.
  • Estimated 100-m resolution ETa were used to quantify agricultural irrigation consumptive water use at a field-scale and incorporated into a basin-wide water-use compilation.

 

National Water Census  •  Colorado River Basin  •  Evapotranspiration  •  Snowpack  •  Water Use   •   Groundwater Discharge