Butte County’s water year runs from Oct. 1 through Sept. 30, 2026, aligning with the state’s seasonal hydrology. Designed by Freepik, www.freepik.com

 

OROVILLE, CA (MPG) - The new water year began Oct. 1 with encouraging signs of above-average precipitation, snowpack and reservoir storage, according to a presentation by Water Resources Scientist Kelly Peterson to the Butte County Water and Resource Conservation Commission.

Butte County’s water year runs from Oct. 1 through Sept. 30, 2026, aligning with the state’s seasonal hydrology. This period captures the full cycle of fall and winter precipitation, spring snowmelt and summer irrigation demand.

According to Peterson, the region is experiencing a rare window of hydrologic opportunity.

“So, it’s a really good time for us in terms of getting a lot of water on the ground … and good conditions to hopefully benefit our groundwater conditions as well,” Peterson told the Water Commission earlier this month.

From snowpack to reservoir levels, the data supports Peterson’s optimism. Northern Sierra precipitation totaled approximately 57 inches as of Sept. 22, about 8 inches more than the previous year and slightly above the historic average. Durham recorded 23 inches of rainfall through July, or 114 percent of its long-term average, while Biggs saw 19 inches, reaching 120 percent of its site average.

The Northern Sierra snowpack measured 31 inches of snow water equivalent on April 1, representing 118 percent of the average for that date. Lake Oroville stood at 63 percent of capacity and 111 percent of the historical average as of Sept. 21, with a storage volume of 2.16 million acre-feet. Oroville’s total capacity is 3.42 million acre-feet, making it the largest reservoir in the State Water Project.

Runoff in the Sacramento River region totaled nearly 20 million acre-feet through August, or 115 percent of the seasonal average. This figure reflects unimpaired flow from upstream rivers, including the Yuba River, and is a key indicator of regional water availability, Peterson said. The Sacramento River basin captures runoff from most rivers upstream of the Delta and plays a critical role in statewide water supply.

Based on runoff indices from four regional rivers — the Sacramento, Feather, Yuba, and American — Peterson reported that the 2025 water year was classified as “Above Normal.” Water year types range from “Wet” to “Critically Dry” and are determined by hydrologic indices that measure total runoff volume. Peterson said the “Above Normal” designation reflects strong surface water conditions but does not guarantee groundwater recovery or drought resilience.

Peterson also reviewed groundwater quality monitoring results from 18 sites across the Butte, Vina, and Wyandotte Creek subbasins. Specific conductivity measurements, used to assess salinity, ranged from below measurable objectives to well above minimum thresholds, particularly in the Wyandotte Creek Subbasin, where some readings exceeded 6,000 microsiemens per centimeter.

Peterson emphasized that elevated salinity levels are linked to ancient marine deposits and fault zone movement near the Sutter Buttes, not coastal seawater intrusion. Monitoring is conducted annually in August during peak irrigation season using probes that measure conductivity and temperature. Wells without pumps are sampled directly, while pumped wells are tested post-extraction.

While Butte County enters the new water year with above-average precipitation, strong reservoir storage, and stable groundwater in most subbasins, the statewide picture remains more uncertain.

The California Department of Water Resources, in its report, warned of increased climate volatility, with a 71 percent chance of La Niña conditions this fall and a growing risk of flood-after-fire events in Southern California.

State Climatologist Michael Anderson noted that California should “expect extremes, dry periods interrupted by large or long-lasting atmospheric river conditions.”

Compared to the driest water year on record, 1923-24, which saw just 17.1 inches of precipitation, the 2025 totals reflect a significantly wetter period. With climate variability increasing, local agencies are focused on capturing and conserving water during these favorable conditions to support long-term groundwater recharge and water quality management.

Sources: California Department of Water Resources, NOAA Climate Prediction Center.

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