Assessing landscape scale heterogeneity in irrigation water use with remote sensing andin situmonitoring

Understanding how irrigation is used across agricultural landscapes is essential to support efforts to growmore foodwhile reducing pressures on limited freshwater resources. However, to date, few studies have analyzed the underlying spatial and temporal variability in farmers’ individual water use decisions at a landscape scale.We compare estimates of irrigationwater requirements derived using state-of-the-art remote sensingmodels withmetered abstraction records for 1400fields over a 13 year period in theUS state ofNebraska, one of theworld’smost intensively irrigated agricultural regions. We show that farmers’ observedwater use decisions often diverge significantly frombiophysical estimates of crop irrigation requirements. In particular, ourfindings are consistent withwidespread use of water conservation practices by farmers in drought years as an adaptive response to rising irrigation costs and regulatorywater supply constraints in these years.We also demonstrate that, in any individual year, farmers observedwater use exhibits largefield-to-field variability, which cannot be explained fully by differences inweather, soil type, crop choice, or technology. Our results highlight the value of using both in situmonitoring and remote sensing to evaluate farmers’ individual water use behavior and understand likely responses to future changes in climate orwater policy.Moreover, our findings also demonstrate potential challenges for current efforts in developed and developing countries to applymodel-based approaches forfield-level water use accounting and enforcement of irrigationwater rights.