In extremely dry years when there is a high premium on surface water, irrigation forbearance agreements help water managers maintain riparian health, fish populations, and ensure water delivery to downstream users. In order for these programs to maximize their effectiveness and limit their impact on agricultural communities, water managers should seek the highest return on investment - or the highest amount of water per acre entered into forbearance. This may be accomplished by assessing the water requirements of fields and then grouping by conveyance lateral, to target the highest among them as good forbearance participants. Unfortunately, irrigation measurement in the Middle Rio Grande (MRG) is done at a low enough resolution that individual use is challenging to tease apart, and the leading remote sensing methodology capable of such assessments is cost prohibitive. For this project, we developed a proof-of-concept remote sensing tool to compare relative water requirements among irrigated fields within laterals in the MRG using freely available data. Raster images for evapotranspiration (ET) and vegetative production (NDVI) were obtained through the EEFlux automated ET tool, and calibrated to local weather stations. Data for soil infiltration rates (saturated hydraulic conductivity, or Ksat) were obtained through the SSURGO soil survey database. ET and NDVI for each field were ranked and compared against one another and averaged by lateral, highlighting laterals using more water relative to their vegetative production. This helped control for fields that were water heavy, but had high agricultural production to show for it. Ksat values were averaged similarly across laterals, highlighting areas where water infiltrates most rapidly and puts high demand surface water underground. By assessing water use not through quantitative methods, but relatively against one another, this tool spatially identifies laterals that show the greatest potential to yield a higher amount of water per acre in the MRG. Identifying these laterals has the capability to improve the return on investment for water managers and potentially lower the number of acres that would need to be fallowed for a desired management effect.
Birt, Trevor. "Irrigation Forbearance in the Middle Rio Grande: Using Remote Sensing to Improve Investments." (2019). https://digitalrepository.unm.edu/wr_sp/181