Abstract:
Wyoming’s interstate streams – the upper Colorado in particular – are facing the threat of curtailment and calls due to reduced water supply with climate change altering weather patterns coupled with an increasing demand for municipal and industrial use with the booming population of the Western United States. Measures are needed to reduce consumptive use and meet targets to ensure Wyoming’s obligations to downstream states are met. These measures can range from full fallowing to applying marginal gains to practices at the basin scale. One option that offers potential for savings without impacting yield is switching to nighttime irrigation on sprinkler fed systems to make the most of times of the day when evaporative demand is low and reducing wind drift and evaporative losses. This approach has the potential to increase on-field irrigation efficiency by ensuring more of the applied water infiltrates into the root zone. We propose a three-year study of a mixed stand of sainfoin/alfalfa/grass on 140-ac under a center pivot in the Bridger Valley. The field will first be evaluated under standard irrigation practices (Year 1) before switching to 24hr cycle on the field with a third of the field designated for nighttime irrigation only (Year 2/3). Each element of the field scale water balance will be directly or indirectly measured (Scintillometer, Weather station, Tipping Bucket, Soil Moisture Probes, Piezometers, Gauging stations). The field intensive approach will be coupled with integrated modelling using a process based hydrologic model to model the field integrating all the different components into a unified framework. This model can then be used both to assess the methodologies tested in the field under different hydrologic and climatic conditions, but also to apply other CCU techniques and compare the results of these different approaches. It is expected that the switch to night irrigation will increase the irrigation efficiency with evaporative losses potentially dropping from 10% to as low as 3%. Some of this will be compensated by an increase in transpiration with more of the water being available in the root zone, depending on the current efficiency, it is also possible that percolation to deep groundwater may also increase. By bringing together the modelling and observed data it should be possible to inform stakeholders of the costs and benefits associated with changing to a nighttime only irrigation schedule and identify what conditions would make for an ideal scenario for the switch.
