California’s landscape has always been appealing, with vast stretches of desert giving way to towering, snow-capped mountains or the waters of the Pacific Ocean. But it is this very climate – where dry summers and wet winters provide the perfect conditions for tourism and agriculture – that’s also the state’s vulnerability.
Everything could be completely dry one year and completely soaked the next. For years, historically dry conditions pushed the West into uncharted territory, resulting in unprecedented water shortages. Then, at the end of December and into the first few weeks of January, a deluge of rain and snow arrived, significantly alleviating the severity of the drought.
However, Californians are aware that the pendulum could abruptly swing the other way: if moisture does not persist and heat sets in, experts fear that the wintertime rain and snow will prime the landscape for an intense wildfire season.
“The dangerous side of this could be – and we’ve seen this in the past – that we get all this moisture, which increases the amount of spring growth around the state, and then all that growth dries out when we don’t get any more moisture and becomes just additional fuels,” Andrew Schwartz, lead scientist at the University of California, Berkeley Central Sierra Snow Lab, told CNN.
What’s there at the end of winter is more important than the amount of moisture in the ground right now, according to Daniel Swain, a climate scientist at the University of California, Los Angeles.
“What’s troubling is that now, in a warming climate, even in some of the wet years, we’re seeing significant or even elevated severe fire activity due to how dry and warm it gets in the intervening months,” Swain told CNN.
While it’s too early to tell, the ingredients for a dangerous fire year are slowly coming together, he added.
This has happened before. CalFire battalion chief Issac Sanchez described 2020 as a “unusual year,” with the season beginning with atmospheric river storms that dumped a lot of rain and snow and fueled vegetation growth across California.
According to the California Department of Forestry and Fire Protection, those conditions quickly turned to drought, fueling record-breaking wildfires that burned more than 4 million acres – the worst wildfire season in state history.
“We can’t predict how many fires will occur this year because we simply don’t know,” Sanchez told CNN. “What we can see is that the conditions for large destructive fires will exist, and we must be prepared when that occurs, because we don’t know when or where the fire will occur.”
According to Scripps Institution of Oceanography, California was hit with nine back-to-back atmospheric river storms this winter. These storms, which were caused by conveyor belts of concentrated moisture in the atmosphere that emerged from the warm waters of the Pacific Ocean, wreaked havoc on the region, causing record rainfall, deadly flooding, debris flows, and hurricane-force winds.
In just three weeks, the storms dumped nearly 12 inches of rain on the state, totaling more than 32 trillion gallons of water. San Francisco received nearly 18 inches of rain in three weeks, which is more than the city received in the previous 12 months combined.
High-elevation snowpack – which acts as a natural reservoir, storing water during the winter months and slowly releasing it during the spring melting season – is now at more than 200% of normal for this time of year, roughly equivalent to what the region sees at the end of the season, on April 1.
“The numbers have been large, but we are still concerned that if we have a prolonged dry and warm period, we may not end up in a favorable position come March and April,” Schwartz said. “We still have a few months left in the water season, and these aren’t static figures.”
Winter storms in California significantly improved the state’s surface drought conditions. As of Thursday, nearly 90% of the state was suffering from some form of drought. However, only three weeks ago, nearly 7 million Californians were classified as being in extreme drought, the second-worst category. That figure has since been reduced to zero.
According to climate scientists, the lack of precipitation, higher temperatures, and an increase in evaporative demand – also known as the “thirst of the atmosphere” – are to blame for the West’s drought reaching historic proportions.
According to experts, these storms were desperately needed. Schwartz said he wants the moisture and snowpack to stay in place to avoid an active fire season.
The storms have also increased soil moisture, which is beneficial to California’s severely parched vegetation. Plant moisture and new growth help to keep California wildfires at bay. The month of April typically has the highest fuel moisture content in the state.
But the moisture must last until then. Storms, according to Kurt Solander, a hydrologist at Los Alamos National Laboratory, could have a significant impact on this year’s wildfires. It all depends on the moisture content of plants throughout the state in late spring and early summer.
“It’s possible that the faucet that’s supplying the atmospheric rivers we’re seeing shuts off abruptly for the rest of the winter,” Solander told CNN. The rain that California has already received “could promote the growth of [plant] fuels,” increasing the likelihood that areas that have burned in the past will burn again.
If temperatures rise in the coming months, the sun may bake out any remaining moisture in the ground. When all of the vegetative fuel runs out, fire problems emerge, according to Lee Turin Dickman, a plant ecologist at Los Alamos National Laboratory.
“Even if it’s not particularly dry, changes in the plant’s dry mass or carbon content can actually make the vegetation drier than you might expect based on weather or climate conditions,” she told CNN, referring to the “spring dip,” a phenomenon in which moisture content decreases.
The winter storms provided some relief to drought-stricken California, but experts predict another dry spell as temperatures rise.
“We continue to see drought in Southern California and most of Nevada,” said Joe Casola, regional director for climate services at NOAA’s National Centers for Environmental Information’s Western region. “That doesn’t mean it won’t rain or snow in these areas; it just won’t be enough in January, February, March, and April to offset some of the drought conditions that we are still experiencing.”
For example, the Metropolitan Water District of Southern California is still under a regional drought emergency as it prepares for a fourth consecutive dry year.
Swain believes that if dry and relatively warm conditions develop in the coming months, they could significantly offset the gains brought by recent snow and rain storms.
And the combination of dry conditions, low humidity, and extreme heat is a recipe for a destructive wildfire season.
“If we have another summer marked by record heat – as we have pretty much every year for the past decade, at least somewhere in the West – then all of that extra vegetation will dry out more or less completely,” Swain said. “By the end of the summer and fall, when the dry season is at its peak, you have a system full of extra vegetation that is just as dry as it would have been.”
California is no stranger to dangerous, landscape-altering wildfires. And scientists have shown that climate change is exacerbating the problem. Solander recently discovered, through his research, that California was the only state where the rate of fire reburns, or areas burned multiple times over the years, had increased and was consistently higher than in other parts of the West.
“The moisture flux from plants during the late spring to early summer months was one of the primary drivers of wildfire re-burns in California,” Solander said, adding that he will have to go back and check the “moisture content of plants across the state during that time to better understand” how fires may play out later in the year.