January 18, 2024

Delta Conveyance Project Can Help Protect Water Supply Reliability Looking Decades Ahead, Modeling Shows

California’s water delivery infrastructure needs modernization. The system was built in the 20th century based on the certainty that snow would fall in the winter, be stored in the mountains as snowpack, then melt in the spring into our rivers and reservoirs. While rain and snow amounts may have been erratic in decades past, that pattern of precipitation was fairly reliable.  

Those patterns are no longer happening. With climate change, we are seeing a new weather pattern with more precipitation falling as rain and less as snow, and more water flowing through the rivers in the winter months. Because this water is not available to be captured in the spring, water managers must find a way to catch it in the winter for use later in the year or risk losing it altogether.

This is what the Delta Conveyance Project will do: capture and move the water when it is available.

An important question for decision-makers is how effective this modernized infrastructure will be in improving reliability of the State Water Project many decades in the future.

That is why we are using modeling to better understand and plan for the future.

While future changes to other water infrastructure, land use or the regulatory environment are likely as a response to the changing climate, the specifics of these potential changes are unknown. Available models do not predict the future, but they can help us to understand, visualize or simulate what may happen, and can be helpful to compare scenarios.

The 2070 modeling done for the Delta Conveyance Project looks at seven possible future “no project” scenarios (if the DCP were not implemented) that examine potential climate change, sea level rise, and responses to those changes (such as land use or regulatory changes) — all based on the best available science from the most trusted sources. It then compares the scenarios to provide a range of possible no project outcomes to help decision-makers with planning decades ahead.

A single climate scenario (known as the “2070 Median”) was crafted to use in the scenario comparisons, based on 64 projections of climate change from available General Circulation Model (GCM) output. GCMs are the most advanced tools available for simulating changes to the climate at global scale based on increasing greenhouse gas. These models represent processes in the atmosphere, ocean, and land surface.

Seven possible no project scenarios for 2070 conditions were developed that collectively include climate change (2070 Median scenario), 1.8 feet and 3.5 feet of sea level rise, land fallowing/demand reduction, reduced exports, and emergency drought actions.

The modeling shows that State Water Project Delta exports are severely impacted under all seven of the scenarios for no project 2070 conditions with a possible reduction in annual average SWP exports of 0.43 to 0.68 million acre-feet (MAF) compared to existing conditions. When the Delta Conveyance Project is added to the seven no project scenarios, the SWP exports are expected to be restored, by negating some or all of this reduction. The modeling shows that the range of changes in annual average SWP exports would be a reduction of 0.24 MAF or an increase of 0.02 MAF with the Delta Conveyance Project under 2070 Conditions compared to the existing conditions.

While modeling does not and cannot behave as a crystal ball, careful and conservative modeling can provide useful comparative context. Read the “CalSim 3 Results for 2070 Climate Change and Sea Level Projections and Sensitivity Analysis” with this important background in mind.