by Jay Lund
After two years of solid drought, and four months into California’s “wet” season, we don’t know if this year will be wet or dry. This is normal for California. But this year’s monthly precipitation “whiplash” is unusual.
For northern California, October was the 2nd wettest October in 102 years of record (400% of average October from one 2-day storm!). November was the 31st driest November (50% of average). December was the 23rd wettest December (160% of average), and January was the 7th driest January on record (16% of average). Wow!
In this dizzying back and forth, where are we overall?
So far, we are the 36th wettest October-January in 102 years of record for Northern California, with 31 inches. Today, we have slightly above average precipitation for this time of year. But forecasts for the next couple of weeks are dry and warm, and snowpack is now a bit below average.
We still have about 2 months left in the wet season. Years like this now have ended up as dry (2002 and 2013) or very wet (1998). So we don’t really know what we would like to know. See Figure 1.
This year is already wetter than last year’s 2021 total, and is as wet as the total precipitation for 2020, the first year of this drought. Reservoirs are refilling, but many remain far from full. (Folsom is doing quite well.) We could easily end up with a dry year like 2013, especially given the dry forecast for the next 2 weeks.
So we are better off than the last two years, but very likely not out of this drought.
We probably won’t know if the drought is over until the end of March.
Even ample precipitation will not entirely end this drought. Many drought impacts to forests, ecosystems, and groundwater will persist for years to come. Even with massive precipitation, agriculture will feel drought effects for perhaps a decade from the need to replenish the additional groundwater it pumped in the previous two years to comply with SGMA. This means substantial additional fallowing of irrigated lands sooner.
Also, a warm winter and spring could reduce runoff and groundwater recharge from precipitation as happened dramatically in 2021. So runoff, which supplies streams, reservoirs, and groundwater, might be less than we’d expect from the precipitation quantity.
In the meantime, stay calm and hopeful, but prepare for both floods and drought, as usual.
Here is a data garden to play in: http://cdec.water.ca.gov/reportapp/javareports?name=8STATIONHIST
Here is a very nice recent podcast on California’s climate, drought, and floods by Dr. Daniel Swain. https://t.co/ouQbskNrwu
Jay Lund is a Professor of Civil and Environmental Engineering and Co-Director of the Center for Watershed Sciences at the University of California – Davis