Central Valley Refuge Management under Non-stationary Climatic and Management Conditions

Agricultural water users represent nearly 65% (23.1 MAF/yr) of the total statewide demand. More than 90% of the demand is concentrated in the Central Valley with 40% in Tulare Basin, 20% in Lower Sacramento and San Joaquin Valley, and 10% in Upper Sacramento Valley. CVPIA refuge deliveries, on the other hand, constitute less than 2% (0.5 MAF/yr) of the total demand. Even then, only 89% of the Level 2 deliveries and 47 percent of incremental Level 4 have been met between 2001 and 2014. Refuge managers cite budgetary constraints and rising cost of water as the major impediment in realizing Full Level 4 deliveries. Some estimates indicate that, on average, the cost of acquiring water has increased 400% since 1990s. Global warming and regional hydro-climatic alterations are likely to further limit state's ability to manage water, reduce total volume of available water and intensify competition for surface water. Historically, reduction in surface water supplies is substituted with groundwater pumping. Long-term overdraft and Sustainable Groundwater Management Act (SGMA) provisions will, however, limit future pumping opportunities. This research examines impacts from a warm-dry climate, peripheral tunnels, groundwater overdraft regulations, and competing environmental flow demands on water deliveries to CVPIA refuges. The study is conducted within a statewide framework using CALVIN---a hydro-economic optimization model of State of California---to capture the physical, environmental and policy constraints in the existing water management system. Sixteen scenarios are analyzed to capture and quantify the hydrologic and economic implications of climatic and management uncertainties on refuge deliveries including (1) climate vulnerability: historical and warm-dry climates; (2) Delta regulations: high and existing Delta Outflows; (3) infrastructure: with and without isolated facility or peripheral tunnels; and (4) groundwater management: with and without long-term overdraft. A separate Spreadsheet Tool is also developed to explore the benefits and implications of inter-refuge trading and optimizing refuge land-use management practices.