Ground water and surface water under stress

Presented at Ground water and surface water under stress: competition, interaction, solutions: a USCID water management conference on October 25-28, 2006 in Boise, Idaho.Includes bibliographical references.Streamflow in much of the western United States originates as snowfall that has accumulated in the mountains during the winter and early spring. During periods of drought, the water supply for a large portion of irrigated cropland in Idaho is at risk of depletion before the growing season ends. In the case of irrigated potato production, early depletion or limited availability of irrigation water can result in substantial financial loss to a producer due to reduced yield and quality and difficulty in harvesting, handling and storing the raw product. Basin wide estimates of available water supply are provided by Federal and State agencies, however, a given producer's irrigation water supply can be vastly different due to water rights based on the Doctrine of Prior Appropriation, which allocates water according to a priority date. To minimize financial risk under drought conditions, potato producers need realistic estimates of available water supply well in advance of the growing season and production management guidelines for economical potato production under limited water supply. To address this need, a methodology for estimating the probability of a water supply shortage that incorporates water right based allocation was developed to assist producers with drought risk management planning. Additionally, the drought tolerance of six commercial potato varieties was evaluated for four widely varying seasonal drought management patterns simulated by irrigation management. The methodology developed to estimate probability of a water shortage on an irrigation district basis is described and results of an economic risk analysis for the six potato varieties subjected to the four drought management patterns is presented. The results show that the probability of a water shortage can vary widely among irrigation districts due to differences in water priority dates. The results of the economic risk analysis show that potato variety selection and irrigation management strategy can substantially reduce economic loss in potato production systems during drought