A web-based platform to assess water supply resilience under climate extremes in irrigated agriculture in the western US: A case study approach for the San Joaquin Valley in California, the Cache Valley in Utah and the Mesilla Valley in New Mexico.

Irrigated agriculture in semi-arid regions such as the western United States will likely face increased volatility in access to water under climate extremes. Competing water uses including community, tribal, urban and environmental, along with higher-temperature driven increases in irrigation requirements will further the gap between available water and overall system demands. This research explores case studies in three regions of the western United States namely, the southern San Joaquin Valley in California, the Cache Valley in Utah an the Mesilla Valley in New Mexico in terms of their future ability to fulfill agricultural water demands while supporting communities and ecosystems using a web platform. The San Joaquin Valley, chronically affected for decades by groundwater overdraft and demand hardening from permanent crops and livestock wet forages, will necesitate substantial reductions in consumptive use via permanent irrigated land idling to meet sustainable groundwater regulation. We present a wide range of scenarios including trading, deficit irrigation and water supply augmentation along with their economic impacts to explore tradeoffs among alternatives. For the Cache Valley in Utah, environmental flow requirements to regulate levels in the Great Salt Lake may require upstream diversion reductions that will likely affect irrigated forages the most. We present varios crop choice scenarios and water exchange to find least cost alternatives considering downstream sectors such as livestock. The Mesilla Valley in New Mexico, supplied by sufarce water from the Rio Grande and supplemental pumping from the underliying aquifer system in dry years, may see an overall allocation reduction presenting challenges for their high value vegetable and tree crops. We examine the impact of potential groundwater regulation and markets to secure future water access for agriculture and competing sectors.