Interannual variability of water productivity on the Eastern Snake Plain in Idaho, United States

Water productivity of crops must be increased to meet global demand for farm products while conserving limited water resources. Throughout the western United States, highly productive agricultural regions face more frequent and severe droughts and must allocate limited water resources among competing uses. Irrigated agriculture accounts for the majority of consumptive water use and has a proportionately important role in managing water shortage. Water productivity accounting helps inform objective decision making regarding these allocations at the regional, local, and farm scales. Publicly available data from several government agencies were re-analyzed and combined to quantify interannual changes in consumptive water use. Water productivity was determined using county-level crop survey data, satellite-based maps of evapotranspiration, and weather records for 21 counties located in the Eastern Snake Plain in the US state of Idaho for nine years during the period 2009–2019. Changes in water productivity over this period suggest trends that correspond to crop-specific irrigation practices, interannual variability in water supply, and regional attempts to curtail water consumption and improve water use efficiency. Results indicate that, at regional scales, water productivity for alfalfa can increase despite or as a result of water limited conditions, increasing from 0.5 to 1.75 kg ha-1 m-3 in some individual counties over the 10 year period, which may indicate increasingly efficient water use. Water productivity of barley and wheat crops also varied year to year, but did not demonstrate clear independence from total water consumption. Instead, irrigated areas and crops with adequate water supply follow a general trend of increased yield with increased water consumption, and the resulting water productivity approximately follows a linear function of actual evapotranspiration.