Winter-run refuge flows with reduced crop acreage A management strategy in the COEQWAL scenario library
This strategy combines Central Valley-wide reductions in irrigated crop acreage with a set of flows on the Sacramento River meant to improve winter run chinook habitat conditions. The flow requirements target flows at two locations on the Sacramento River but are scaled back or deactivated to balance coldwater storage conditions in Shasta Reservoir. The aim in combining these two actions was to explore the benefit of offsetting reservoir releases the winter-run refuge flows require with a lower overall system demand.
This brief describes a scenario that combines lower valley-wide agricultural demand with flow and storage actions to improve winter run chinook salmon habitat, one of 28 management strategies in the COEQWAL scenario library. Each strategy is simulated once under each of five hydroclimates; the references note at the end of this brief lists the model runs.
A variant of this strategy, Winter-run refuge flows with reduced crop acreage and reintroduction, adds one action that is not a water management action: reintroduction of winter-run Chinook salmon to cold-water habitat upstream of Shasta Dam. The two strategies share the same CalSim 3 simulation; modeled results differ only for the winter-run salmon key outcome.
§2 What this strategy changes
The strategy combines two changes. The first is the reduction in irrigated acreage across the Central Valley. This reduction is the same as that used in the “Groundwater pumping limits via reduced crop acreage in the Central Valley” scenario. The second is a set of winter-run refuge flow actions that attempt to balance the benefits of elevated late winter and early spring flows on the Sacramento River for out-migration with the benefits of conserved coldwater storage in Shasta Reservoir for summer habitat. Flow targets are selected from a set of lookup options at two locations on the Sacramento River using a projection of Shasta storage each month January through March. If projected Shasta storage falls below certain thresholds, some reductions in CVP allocations are made while the flows are reduced or eliminated altogether. Due to the uncertainty of water supply within the CalSim3 simulation, these projected storage and flow adjustments may not always guarantee an optimal balance between the use of flows in the outmigration season and the conservation of storage for coldwater management season. An additional flow target is set on the San Joaquin River to enhance conditions on that system. There are no additional actions to adjust for storage impacts in the San Joaquin region.
The second is a reduction in irrigated acreage across the Central Valley, set according to historical groundwater decline in each demand unit, with reduced acreage replaced by an unirrigated “native vegetation” land-cover type. Groundwater pumping is limited indirectly, through the reduced demand.
The aim in combining reduced acreage with the winter-run refuge flows was to explore the feasibility of offsetting the high reservoir-release demands of the winter-run refuge flows with a lower overall system demand.
§3 The configuration in detail
The table compares the eight operational fields that define this strategy against current operations — the strategy that represents existing operational rules, recent (2020) land use, and TUCPs. Rows that match current operations are shown in light gray; rows that differ are highlighted.
| Aspect | Current operations | This strategy |
|---|---|---|
| TUCP actions | Active | Active |
| SGMA actions | None | Limit irrigated acreage for the entire Central Valley |
| Land use | 2020 LandIQ | 2020 LandIQ with reduced agricultural acreage in selected areas across the Central Valley |
| Delta regulations | Standard | Standard |
| BiOps | 2019 / 2020 ITP | 2019 / 2020 ITP |
| Infrastructure | Standard | Standard |
| Flows | Standard | Functional flow requirements at 17 locations (tributaries plus Delta) |
| Allocation / priorities | Standard | Standard |
§4 Lineage and source
This scenario was created by the COEQWAL team by combining the winter-run refuge flows scenario with the reduced-acreage land use of the Central Valley groundwater scenario. The scenario uses DWR's adjusted historical hydrology and does not modify operating rules beyond the flow and demand adjustments. The CalSim model files for this strategy are referenced by the run IDs in the references note at the end of this brief.
§6 What this doesn't say
This brief describes a scenario representation in CalSim, not a real-world policy proposal or implementation plan. The strategy as modeled may not capture all details necessary to support direct translation to actual operations. The brief does not predict, evaluate, or recommend any outcome — it describes what the scenario changes about CalSim's representation of the system. For what the model produces under this strategy, see the result briefs referenced in §7.
§7 See results for this strategy
To see modeled outcomes under this strategy across all nine key outcomes at the reference hydroclimate, see the Rivers, salmon and the Delta ecosystem theme brief.
To see outcomes at a specific location of interest, see the relevant LOI briefs — particularly those for locations on the Sacramento River and for groundwater basins in the Central Valley.
References — model runs
Each strategy is simulated once under each of five hydroclimates. The table lists the model run behind this strategy and the current-operations run it is compared against, for each hydroclimate, so any reader can trace this page to specific CalSim runs.
| Hydroclimate | This strategy | Current operations |
|---|---|---|
| Historical hydroclimate (adjusted) | s0033 | s0020 |
| Moderate climate stress (EC-Earth3-Veg) | s0146 | s0134 |
| Moderate-high climate stress (cc50) | s0074 | s0047 |
| High climate stress (cc95) | s0094 | s0056 |
| Extreme climate stress (TaiESM1) | s0120 | s0108 |