What will it take for California drought to end? It’s way more complicated than ‘rain’

While drought does come and go, rain can bring some relief, according to the U.S. Geological Survey. But exactly how much precipitation it would take to end the California drought is complicated.

A major storm, like the bomb cyclone Northern California saw last month, can help — but it won’t end water woes.

“It is important to remember that drought is a naturally recurring feature of our climate in California, and droughts will never completely go away,” said Michelle Stern, a hydrologist at USGS. “Droughts and floods are central to California’s past, present, and future.”

The agency said on its website that light to moderate showers bring temporary, cosmetic improvements; whereas, rain from thunderstorms mostly go to drains and streams and not into the ground.

Storms that can best alleviate drought are ones where rain soaks the soil, recharges groundwater, and “sustains vegetation and feeds streams during periods of no rain.”

How rain can improve the drought

In terms of improving drought, Richard Heim, a meteorologist at the National Oceanic and Atmospheric Administration’s National Centers for Environmental Information, said that soil moisture, rivers, groundwater and reservoirs need to be taken into account, as each of these factors needs different amounts of rain to recover.

“The drought created a deficit of soil moisture storage, empty reservoirs, and groundwater that has been overdrafted for decades,” Stern, with USGS, said. “Surface reservoirs and soil moisture can recover in one wet season, whereas groundwater takes one to tens of thousands of years to recover.

“Atmospheric rivers are key to refilling our surface reservoirs and soil moisture, but we need more than one to get us back to normal conditions.”

An atmospheric river is a stream of intense water vapor that cools and produces heavy rain and snow. This type of phenomenon can provide up to 50% of the West Coast’s water supply, the U.S. Department of Energy said on its website.

This year marks the second driest year on record. Last month, Gov. Gavin Newsom extended the drought emergency across California.

What California needs to recover

According to the USGS and the hydrology team at the California Department of Water Resources, California needs 140% of precipitation to reach average runoff conditions.

The average amount of precipitation in California is 23 inches per year, Stern said. California would need 140% of that — roughly 32 inches — to recover.

The average across California in October was 4 inches. This year, the state would “need an additional 28 inches of precipitation ... to recover to average runoff conditions,” Stern said.

Essentially, with 140% of rainfall, there will be a sufficient amount water to moisturize the soil to conditions where runoff to the reservoirs is possible.

“It helps to think of soils like a sponge; when you first wet a sponge, water must completely saturate the sponge before water starts to spill over,” Stern said. “It will take many storms once the soils are saturated to create enough runoff to refill California’s larger reservoirs.”

Depending on the severity of the drought, different regions will need more or less to see significant improvements.

How to tell drought ended

Identifying the end of a drought is complicated because of its many definitions.

Simply put, drought is the absence of water. According to the NOAA, there are different types of drought: meteorological, hydrological, agricultural and socioeconomic. You can experience more than one type at a time.

“The surface water drought can be considered over once the major reservoirs are refilled,” Stern said. “Landscape (soil moisture and vegetation) and groundwater droughts are more difficult to declare ‘over’ because they are variable across space and time and are more difficult to measure.”

La Niña winter

There’s doubt as to whether California will have a wet season to that extent.

“There are relatively few years in California’s historical record in which we’ve had 140% or more of average precipitation,” said Jeanine Jones, the drought manager at DWR. “So that’s another way of saying that the odds of getting the average run off this year aren’t good.”

The National Weather Service announced last month that California had a high chance of experiencing its second consecutive La Niña winter. And while the season is starting off wet, forecasts show that it may get drier in the later phase.

Jones said it won’t be until the end of the wet season, around March or April, that we can see what the drought conditions look like and whether it improved.

“Something else to keep in mind is that California has the highest variability of precipitation of any state in the United States,” she said, “meaning that it’s very easy for us to swing from a very wet year to a very dry year or anywhere in between.”

Stern said, in the meantime, individual actions to conserve water and reduce water usage are important. It’s also key to consider how agencies manage the state’s reservoirs, snowpacks and groundwater resources during times of drought and flood.

This story was originally published November 4, 2021 at 6:00 AM with the headline "What will it take for California drought to end? It’s way more complicated than ‘rain’."