Climate Change Informational Webinar Highlights


Historical and projected California snowpack

Historical and projected California snowpack.

Rain and snowfall in California have always been inconsistent and unpredictable. It is our climate’s natural state. The realities of climate change, that take the inconsistent nature of precipitation in California to an extreme, are making water management that much more of a challenge. The proposed Delta Conveyance Project is just one way the state can adapt to help ensure a reliable supply of water for our cities, farms and environment in this new normal.

The Department of Water Resources (DWR) recently hosted a series of webinars to provide background information related to preparation of the Draft Environmental Impact Report (EIR) for the Delta Conveyance Project, including one on climate change. The webinar specifically covered 1) the effects of climate change on water supply in general and in the project study area, and 2) how the environmental review for the proposed project will analyze climate change, including assumptions and methodology.

The presentation focused on several elements, including an overview of climate change planning in California such as DWR’s response, the purpose of the climate change analysis in the Draft EIR, and the evaluation methods and assumptions that will be used in the Draft EIR. Specifically, the information addressed what climate change is, how California has a uniquely variable climate, projected climate changes and how the proposed Delta Conveyance Project is a key component of the state’s response.

As the proposed Delta Conveyance Project is analyzed in the Draft EIR, it is important to keep in mind this information about climate change in general and how climate change will be considered in the Draft EIR:

How is California’s Climate Changing?

It used to be that a fair amount of our precipitation would fall as snow in the winter months. That snow would stay in the mountains through spring. From November through March, our reservoirs would be used for flood control, holding and releasing water for public safety. In April, the reservoirs would then be used to catch the melting snow, and water managers would hold and release much of that water to maximize water supply for people, farms and the environment.

As DWR described in the webinar, with climate change, this is no longer the case. Climate trends show that we are seeing less snow and more rain in the winter months. When we do see rain, it is even less predictable than before, and it tends to be flashier. This means more and longer droughts and more intense rain events. Other trends include increasing water temperatures, rising sea levels and increased sea water intrusion, and an earlier spring runoff.

How Will the Delta Conveyance Project Help?

Existing water supply infrastructure isn’t built to accommodate these new climate realities. The proposed Delta Conveyance Project would help State Water Project (SWP) managers catch, move and store SWP water when it is available. It will do this by building new facilities to move the water more efficiently.


How Will DWR Evaluate Climate Change for the Delta Conveyance Project?

DWR will release a Draft EIR in mid-2022 to evaluate the proposed Delta Conveyance Project under the California Environmental Quality Act (CEQA). As described during the informational webinar on climate change, the Draft EIR will address climate change issues by answering three fundamental questions.

  1. How could climate change impact the study area? This includes analyzing air quality and greenhouse gas emissions caused by project construction and operation and how the project might contribute to the occurrence of climate impacts.
  2. How could proposed project impacts (unrelated to project emissions) on resources in the study area be affected by climate change? This includes looking at hydrologic modeling to consider future conditions with climate change.
  3. How could the project affect the resiliency of the study area or California water resources? This includes looking at how effectively the project can help the state’s water resources systems adapt to climate change.

DWR is Using the Best Available Science

Answering many of these questions requires identifying, understanding and using the best available climate science to model and forecast a future with climate change, and then analyze and evaluate that future with regard to the proposed project.

Climate modeling projections are based on complex ocean and atmospheric models of the earth’s system that use mathematics to mimic the system and provide information about how the atmosphere and greenhouse gas emissions are expected to evolve. But since these models are global, they must be downscaled to a regional level.

One aspect to understand about modeling is that it is based on future variables that simply cannot be known with certainty. For this reason, most climate modeling will provide a range of possible scenarios. The assumptions for these scenarios are key to understanding analyses and resulting findings.

A Note About Assumptions

As members of the public review the Draft EIR, it will be important to keep in mind that assumptions for engineering and design are different than assumptions for environmental review.

Assumptions for project engineering and design are conservative to ensure that the project is durable and protected from flooding. The engineers therefore consider climate change conditions, including runoff patterns and river elevations, in the year 2085, as well as a 200-year flood risk.

On the other hand, to conduct the environmental review requires a comparison of the proposed project to existing conditions baseline and an evaluation of reasonably foreseeable, likely future conditions focused specifically on operations of the SWP and the Central Valley Project. Sea level rise, temperature and precipitation will be evaluated based on today’s conditions as well as projections for the year 2040 using a combination of both climate and hydrologic modeling.

About the CEQA Climate Change Analysis

While CEQA does not prescribe specific requirements on how project proponents evaluate climate change, DWR is utilizing guidance provided in its Phase II Climate Change Analysis Guidance document published in 2018. This guidance includes very detailed methods to incorporate climate change impacts for public disclosure and informational purposes.

To look at climate trends, DWR is also relying on the Intergovernmental Panel on Climate Change’s Fifth Assessment Report published in 2013. Data from the Sixth Assessment Report will be incorporated when feasible. Other studies utilized include the California Fourth Assessment Report, several DWR studies that contributed to that Fourth Assessment Report and several other research papers specific to California.

The Draft EIR will help evaluate how, and how well, the Delta Conveyance Project may help address climate change and improve the resiliency of the SWP into the future.

To learn more and stay informed about the Delta Conveyance Project: