The estimated cost of the proposed tunnel beneath the Sacramento-San Joaquin River Delta has risen to $20.1 billion.

Officials say the project is vital to improving the reliability of water supplies in the face of climate change, sea-level rise and the risks of an earthquake. Current infrastructure could be out of commission for months if it were hit with a significant climate disaster.

For more on this, KCBS Radio's Holly Quan was joined by Peter Gleick, Senior Fellow and co-founder of the Pacific Institute and member of the U.S. National Academy of Sciences.