October 1 marks the beginning of California’s new Water Year (WY). Water years here run from October 1 until September 30 of the next calendar year and are named for the calendar year of the bulk of the water year (January – October). October 1 is also the nominal beginning of California’s wet season. (No significant rain yet, by the way.) California’s hydrology has two basic seasons, wet and dry, with the wet season nominally from October 1 – April 1 (Figure 1). The first sizable storm sometimes arrives in late September and sometimes not until November (recently in 2021). Sizable storms rarely arrive after April. As we leave California’s long 2026 dry season and prepare, hopefully, for the wet season, it is good to reflect on the last water year and prepare for what is also California’s flood season. 

Other water year news:

• KTNV (Las Vegas): New water year begins with cuts on horizon
• KCRA (Sacramento, Calif.): How did Northern California do at the end of the water year?​
• The Ukiah Daily Journal (Calif.): Lake Mendocino in 2026: 10 inches less rain, five feet less storage
• California Department of Water Resources: News release: As new water year begins, California prepares for strong El Niño and expanded water supplies