Happy New Water Year 2023!

by Jay Lund

Happy New Water Year, 2023!  (October 2022 – September 2023)

The first New Year celebration for California’s water wonks is October 1, the beginning of the new Water Year, the nominal beginning of California’s wet season.  California sometimes has its first big rain storm earlier, and sometimes later, but by convention the wet season begins October 1.  It is a time when reservoir levels are reduced to prepare for potential floods (not an issue this year because of already-low reservoir levels) and when notices of flood vulnerability are sent to many residents of low-lying areas (which remain vulnerable during the coming wet season despite relatively low reservoir levels upstream).

Outlook for 2023 Water Year

The outlook for the 2023 water year is that it is far too early to tell.  We have had some precipitation in September, which helped suppress wildfires, but didn’t contribute much to water supply.  Hopefully we will have more and larger storms starting this month, but not so much as to cause floods.

Reservoir levels in California are mostly well below average for this time of year, and soil and groundwater levels remain below average from the past three years of drought.  The Colorado River reservoirs are in trouble.  Temperatures (and watershed evapotranspiration) seems persistently high.  All this means that water shortages in this new water year will be magnified even if 2023 is dry to even moderately wet.

At this time of year, media and pundits ponder the entrails of El Nino, La Nina, and ENSO indices for prognosticating how wet the coming year will be.  But for northern California, ENSO is poorly correlated with runoff, as seen in the figure below (Schonher and Nicholson 1989).  Jan Null just blogged his statistical analysis of El Nino, La Nina, and precipitation for different basins in California with seemingly similar findings.

ENSO and Sacramento Valley Annual Runoff

The statistical truth seems to be that there is little well-documented skill in predicting what the current water year will bring until well into the water year, perhaps even February or March.

Effects of the last three drought years endure

Even if the coming year is wet enough to fill reservoirs, there will be enduring effects of the last three drought years (and earlier drought years).  The most recent drought years are likely to have increased dead or dying trees in as-yet unburned watersheds, contributing to increases in fire risk and air quality problems for some years to come.  And the reductions in groundwater levels from recent drought years will make achieving groundwater sustainability more difficult (Escriva-Bou et al. 2020). 

“Drought management” must extend well beyond hydrologic drought years, just as most flood management, preparations, and investments must occur in non-flood years.

Prepare for both dry and wet, perhaps both in the same year

Californians and California’s water managers need to prepare for the new water year to be both wet and dry, as both dry and wet years are possible.  Even dry years sometimes include flood or near-flood events, at least locally.

Welcome to California water management.  Hope for the best, but prepare for the worst.

May Water Year 2023 be wetter than California’s 2022 and drier than Florida’s 2022!

Further reading

Escriva-Bou, A., et al. (2020), How reliable are Groundwater Sustainability Plans?, CaliforniaWaterBlog.com, 20 May.

Null, Jan (2022), La Niña and California Precipitation, October.

Schonher, T. and S. E. Nicholson (1989), “The Relationship between California Rainfall and ENSO Events,” Journal of Climate, Vol. 2, Nov. pp. 1258-1269.

You can play with the figure’s data yourself, with data cheerfully supplied from DWR’s CDEC: http://cdec.water.ca.gov/reportapp/javareports?name=WSIHIST and NOAA: https://origin.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ONI_v5.php

Jay Lund is a Professor of Civil and Environmental Engineering and Vice-Director of the Center for Watershed Sciences at the University of California – Davis.

About jaylund

Professor of Civil and Environmental Engineering Director, Center for Watershed Sciences University of California - Davis
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