Pairing Water Rights to Land Parcels -- Connecting the Prior Appropriations Doctrine and Croplands in the western US

Agricultural production in the western United States faces uncertainty with climate change leading to reduced crop yields from higher temperatures, lower precipitation rates, and shifting the growing seasons. This impacts farmers and their livelihood but more broadly, the United States's food supply and economic activity. While climatic characteristics are necessary to understand how crop production in the western United States will shift, many studies neglect the role that the water rights priority system plays in determining which croplands receive water under drought conditions. This study introduces a methodology to pair water rights, including priority dates, to land parcels and irrigated croplands. Crops were analyzed within hydrologic and state boundaries to determine which are at risk under the water rights priority system in drought conditions. Lastly, outputs from a global hydrologic model were used to assess water availability under common large-scale water allocation schemes versus the priority system in practice in the western United States, to evaluate schemas impact on water's spatial distribution. The novel pairing of land and water rights in this study increased water right boundaries from 29 to 59 percent across 10 states by implementing spatial overlays, radius, and waterway methods, with the spatial overlays achieving the highest accuracy. Median priority dates of the nine most cultivated crops in the western United States revealed a hierarchical system for water rights seniority, with oats and other hay having the most senior water rights, while junior water rights showed less of a hierarchy, although corn appeared to have the most junior water rights. This study is significant as it establishes a novel framework for linking water rights to croplands, enabling regional-scale analysis and introducing a methodology to integrate this data into a global hydrologic model to achieve insights on a field-level.