St Mary-Milk Rivers Consumptive Use Study – Remote Sensing Component (Phase 4)

Evapotranspiration, which is the transfer of water from land to the atmosphere from soil and plants, was first estimated in the St. Mary-Milk basin in 1986 by R.E. Thompson Jr. Additional estimates were conducted in 2015 in an earlier phase of the St. Mary-Milk Rivers Consumptive Use Study, which has been in progress for over a decade; this study is now in its remote sensing component. In the first 3 phases of the remote sensing component, actual evapotranspiration (ETa) from 1982-2018 was calculated using remote sensing, then recent ETa was estimated on a 2-4 week interval using satellite imagery.  

This project represents Phase 4 of the St. Mary-Milk Consumptive Use Study’s Remote Sensing Component. The goal of Phase 4 is to create a consumptive use data product for the Milk River basin using the dataset of irrigated lands from Phase 2, and the ETa estimate data from Phase 3. The ETa estimate data will then be contextualized to irrigated lands specifically, which will then be used to calculate long-term trends in consumptive use seasonally. These consumptive use patterns will also be compared to drought indices to determine periods of drought conditions within the basin.  

Evapotranspiration is an important factor in determining apportionment of water from the St. Mary and Milk Rivers . Phase 4 will build a better understanding of the watershed by determining how much water has been used on irrigated lands historically in the Milk River basin, including during periods of drought. This will provide up-to-date information on water use. The project deliverables (maps of historical ETa and up-to-date monthly ETa) will be useful in fostering outreach with stakeholders and water users in the basin.