by Jay Lund
March is usually the last month in California’s mostly unpredictable wet season. A dry March can make a promising water year disappointing. A very wet March can make a potentially critically dry year be only mildly dry, like the “Miracle March” of 1991 (with three times average March precipitation).
Unlike basketball, nobody prevails in California’s annual March Water Madness. The outcome is usually a combination, rather than unmitigated win or loss. Below is a bracket for March 2024, where the outcome for the water year consolidates with time, with diminishing room for surprises.
Marches past and present
The distribution of March precipitation for northern California appears below. It averages about 6 inches per year and ranges from 0.5 inches (1923) to 23 inches (1995), big enough for floods. The “Miracle March” of 1991, the 4th year of drought, was only 18 inches, but three times average March precipitation. Last year (2023), was drier in northern California than in the San Joaquin Valley, but had 17 inches in March. 2017, the wettest water year on record for norther California, had only 17 inches precipitation in March.
Historically, there is only a 5% correlation between February and March precipitation, so we go into March as the last wet month hoping for the best, but not very confident of any predictions. Beware the guides of March.
March this year
We are long enough into March to see that this March’s precipitation is unusually average, about 6 inches. And for northern California, water year precipitation is also about average, with a little better than average snowpack. The San Joaquin Valley is about 80% of average precipitation, with snowpack doing a little better, but slightly less than average, so far. Southern California has had a wet water year, with floods. California is too big and diverse to usually experience the same water year.
For 2024, no outcome has prevailed statewide. We have outcomes that are average, a bit wetter than average, and a bit drier than average. This is the hand we have been delt, which fortunately also included excellent reservoir storage left over from last year.
The major state and federal water projects announced an increase in allocations this week, doubtlessly satisfying to those with higher-priority contracts and disappointing those with lower-priority contracts.
Another wet season is coming to an end.
Further reading
Precipitation:
Northern Sierras: https://cdec.water.ca.gov/reportapp/javareports?name=PLOT_ESI.pdf
San Joaquin Basin: https://cdec.water.ca.gov/reportapp/javareports?name=PLOT_FSI.pdf
Tulare Basin: https://cdec.water.ca.gov/reportapp/javareports?name=PLOT_TSI.pdf
Snowpack: https://cdec.water.ca.gov/snowapp/sweq.action
Reservoir storage: https://cdec.water.ca.gov/reportapp/javareports?name=RESSW
