Climate Change and Water Resources Challenge in California Francis I Chung, Ph.D., P.E. Department of Water Resources

Outline Challenges in Water Management CALSIM, DSM2, and CVGSM Interfacing CALSIM with DSM2 Impacts of Climate Change on Water Resources Inputs for CALSIM and DSM2

Water In California Population Agriculture Projected Water Shortage

Two Possible Strategies to Cope with Climate Change Prevent or Minimize –Define Cause and Effect –Implement Prescriptive Actions Adapt –Define Possible Consequences with Probabilities –Devise Adaptive Actions to Minimize Negative Impact

Challenges in Water Resources Water Supply Floods and Droughts Sea Level Rise Crop ET Groundwater Ecosystem Water Quality Power Generation

Comparison of CALSIM and DSM2

Figure from Bulletin California’s Major Water Projects State Water Project Central Valley Project (Federal) Local

Relationship between Model Outputs Outputs shaded blue provide input to the next model. Global Climate Models CA Output Precipitation Snowmelt Soil Moisture Evapotranspiration Temperature CALSIM Output Reservoir operations Project deliveries Delta inflows and exports DSM2 Output Flow Stage (water level) Salinity Other water quality constituents

Statewide CVP & SWP Water Allocation Model CALSIM State Water Project Central Valley Project (Federal) Local

CALSIM General-purpose water resource systems model Developed by DWR’s Bay-Delta Office and the Bureau of Reclamation Accounts for system operational objectives, physical constraints, legal and institutional agreements and/or statutes It is a simulation model that uses a daily or monthly time step to look at reservoir release decisions and surface water allocations

Salinity Constraints CALSIM uses an Artificial Neural Network (ANN) to compute Delta salinity ANN relates flow (inflow and exports) to salinity ANN was trained on historical data ANN runs in a few minutes or less

Groundwater modeling Groundwater elevations are simulated using multiple-cells Multiple cell model emulates CVGSM, a quasi-3D non- steady finite element model of the Central Valley Darcy’s law used for subsurface flow and stream-aquifer interaction Unconfined (single) layer in Sacramento basin, and Confined/Unconfined (multiple) layers in San Joaquin basin Multiple cell model calibrated against CVGSM Continuity equations for multiple cell model imbedded directly as constraints in CALSIM

Calsim Hydrology Hydrology is the time series estimate of Central Valley water supplies for areas tributary to the Delta at a future level of land use development Historical trace of precipitation (monthly) Land use categories: Ag (crops), Urban, Native, and Riparian vegetation Demands for water are land use based using consumptive use model Local accretions calculated using a water budget for each area at a historical level and then modifying it for future land use level Depletion Study Areas

Bay-Delta System San Francisco San Diego Redding Los Angeles Bay-Delta detail image from CALFED Sacramento Stockton San Francisco Sacramento River San Joaquin River DSM2 Domain

Running DSM2 to Simulate Delta Conditions QUAL Delta Geometry Initial Hydrodynamic Conditions Martinez Tide Delta Inflows and Exports Delta Island Consumptive Use Withdrawals and Return Flows Delta Structure Operations HYDRO Delta Geometry Initial EC Conditions Delta Hydrodynamic Conditions Martinez EC EC in Delta Inflows EC in Agriculture Return Flows Delta EC

DSM2 Grid Image from USBR GIS Group

Design Repeating Tide vs. Realistic Tide Spring Neap Moon Phases

CALSIM DSM2-HYDRO DSM2-QUALDSM2-PTM 72-year Hydrology 2020 Demands Project Island Operations Delta Barriers Martinez Tide Particle Transport / Fate ECDOC

Calsim Input: Time Monthly or Daily Time-step Level of development –Agricultural acreage, growing season, etc. –Urban population hydrologic events (adjusted to level of development)

Calsim Input: Physical Constraints System representation Reservoir storage & outlet capacities Export capacities Canal, conveyance and river capacities

Calsim Input: Hydrologic Inflows Reservoir inflows –Streams –Precipitation/evaporation Local flows Surface-groundwater interaction Return flows Forecasting

Calsim Input: Regulatory Constraints & Agreements Minimum in-stream flows Export reductions Delta salinity standards Temperature standards Delta cross channel operation COA: Coordinated operations agreement CVPIA b(2) protections EWA protections

Calsim Input: Operating Rules Allocation priorities Reservoir operations (flood control, rule- curve, carryover, balancing) Project demands/allocation procedure Non-project demands

DSM2 Boundary Conditions HYDRO Flow Velocity Water Levels San Francisco San Diego Redding Los Angeles Sacramento Stockton San Francisco Sacramento River San Joaquin River Exports Tidal Stage Consumptive Use Tributaries Bay-Delta detail image from CALFED QUAL Constituent concentrations

DSM2 HYDRO Boundary Conditions Tidal flows from the ocean –Represented by stage (water level) at Martinez –Calculated from astronomical tide Inflows from major tributaries –Precipitation and runoff are reflected in inflows, but are not directly input into DSM2 –Provided by CALSIM simulation results or historical data Exports and diversions –Federal, state, and local diversions –Delta Cross Channel Operations –Provided by CALSIM simulation results or historical data Delta Island Consumptive Use (DICU) –Agricultural diversions –Agricultural return flows –Computed from a DICU model Stockton San Joaquin River Delta Island Consumptive Use Eastside Streams Sacramento River Yolo Bypass Exports Martinez Tidal Stage Sacramento Martinez Delta Cross Channel

DSM2 QUAL Boundary Conditions Boundary conditions are required for each constituent simulated –Conservative constituents (e.g. EC) –Non-conservative constituents (e.g. DO) Concentration of each constituent at each inflow boundary –Ocean (represented at Martinez) Provided by historical data or estimates from an Artificial Neural Network (ANN) –Tributary rivers and streams Provided by historical data or other estimates –Agricultural return flows Typically EC is simulated and then converted to other constituents due to lack of field data Stockton San Joaquin River Delta Island Return Flows Eastside Streams Sacramento River Yolo Bypass Sacramento Martinez Ocean sources

Concluding Remarks Key Models on Water Management are available in California Inputs to Models are needed to account for climate change Scientific Uncertainties on Inputs need to be identified Operating rules need to be developed to account for adapted operations

Contact Information Francis Chung, Ph.D., P.E