Justin Huntington, Matthew Bromley, Charles Morton, Tim Minor, Greg Pohll, Jim Thomas
Reporting of evapotranspiration from irrigated agriculture in Nevada and other western US states is increasingly being required for surface and groundwater use inventories, estimating historical pumpage, and supporting the evaluation of water right applications, transfers, and protests. The arid landscape of northwestern Nevada is punctuated by agricultural communities that rely on water supplied by the diversion of surface waters, groundwater, or a combination of both. Many hydrographic areas (HAs) within northwestern Nevada are entirely reliant on groundwater due to the lack of surface water, while other HAs are entirely reliant on surface water due to poor quality of groundwater. Precipitation in the form of winter snowfall largely determines the amount of surface water that is available for irrigation the following growing season. During years of insufficient surface water supplies, some basins can use supplemental groundwater in order to meet irrigation needs.
The use of satellite imagery is required to accurately estimate actual evapotranspiration (ET) from irrigated agriculture. Because crop type and field conditions can vary significantly in time and space, satellite imagery such as Landsat that is of sufficient spatial resolution to capture field scale conditions, is required to accurately characterize spatial and temporal variations of crop phenology, stress, and ultimately ET. Free access to satellite imagery and gridded weather data along with significant advances in processing hardware, software, and analysis, has advanced the use of satellite imagery to the forefront of ET estimation. This is especially true where water consumption from large areas has to be quantified.
The objective of this study is to estimate ET from irrigated agriculture in northwestern Nevada from 2001 through 2011 using Landsat satellite imagery. Estimated ET is evaluated with respect to variations in climate, water supply, and land use changes, through visualizations and summaries of spatial and temporal ET distributions for focused study areas northwestern Nevada. A geodatabase was constructed that includes monthly, seasonal, and annual ET, precipitation, net ET (ET minus precipitation), and atmospheric water demand (i.e. reference ET) for each study year and HA within the study area. Landsat based ET was estimated using a land surface energy balance model, Mapping EvapoTranspiration at high Resolution with Internalized Calibration (METRIC), using Landsat 5 and Landsat 7 imagery combined with reference ET.
See the following links for the report, appendices, and geodatabase.
- Appendix 1
- Appendix 2
- Appendix 3
- Appendix 4
- Appendix 5
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