Monday December 2, 2024
Valley Ag Voice —
Roughly every two years, the California Department of Water Resources issues its “Delivery Capability Report” for the State Water Project (SWP). Those studies estimate the amount of SWP water that can be delivered each year, based on simulations of current facilities and regulations applied to over 70 years of historic hydrology. The first study conducted in 2001, indicated that on average, 72% of contracted water entitlements could be delivered annually. During a 6-year drought, average deliveries would drop to 41% of the contracted amount. Since then, regulations to protect endangered fish have reduced exports. DWR just released its 2023 Delivery Capability Report. Average annual deliveries are now estimated at 55% of contracted entitlement with deliveries through a six-year drought now expected to be 23%.
Usually, the Department will also provide forecasts which consider predictable future changes in supply. In the 2023 report, they considered the consequences of different levels of climate change. Climate change is expected to affect project yield in two ways. First, more precipitation is expected to come as rain rather than snow. Reservoirs that are being operated for flood protection have to release that runoff to preserve capacity for future flood events. Those releases do not often result in an increase in exports because there is no additional capacity available downstream to store that water. Second, with sea level rise, additional freshwater releases are needed to push salinity intrusions to maintain water quality for in-Delta uses. In the 2023 report, the Department considered three climate change scenarios (50%, 75%, and 95% level of concern). The middle one suggested average SWP deliveries would be 44% of contracted entitlement and the six-year drought would be 15%. Compared to the studies in the 2021 report, that is a loss of 28% of contract entitlement — around 280,000-acre feet per year for Kern County. The losses through a six-year drought are lower but similar.
The declines in SWP deliveries not only impact deliveries of regulated supplies for irrigation, but they also affect the quantity of water available for recharge – the “Article 21” water from the SWP. In 2001, the annual average was 130,000 af/year. That’s down to 86,000-acre feet per in the 2023 study, factoring in climate change. That water, stored in wet years, is recovered in dry years and is desperately needed in Kern County to endure droughts.