The drought situation in California is improving this year compared to the same period last year.
In November 2021, more than 80% of California was experiencing extreme drought or worse, up from about 43% this year, according to data from the US Drought Monitor. The data is updated weekly and shows drought conditions across the country.
Aside from the San Joaquin Valley, exceptional drought conditions have been trampled across the majority of the state. This means East Bay and North Bay cities like Oakland, Napa and Walnut Creek are finally out of this most severe drought designation.
The California coast has also seen significant improvements this year. San Francisco, Los Angeles and the Big Sur coast quickly went from “extreme” to “severe” after recent rains. “A wet week for much of the west helped kick start the current hydrological year after a slow start,” the current drought monitor summary reads.
In recent years, La Niña weather conditions have crushed early season storms as they approach California, but this year was different.
Towards the end of September, the state experienced a solid downfall when a rainstorm flooded the Bay Area and the Sierra. October ended up being dominated by fog that replenished the redwoods and other flora along the Santa Cruz Mountains. And November saw an atmospheric low river producing rain and snow showers in every corner of the Southern Cascades, the Tahoe region along the Sierra Nevada, the San Bernardino Mountains and the Coast Mountains along the Highway 1. The Bay Area also experienced several rounds of downpours. last week bringing up to an inch of rain to downtown San Francisco and nearly 2 inches of rain to the East Bay Hills and North Bay Valleys.
Last year’s rainy season – the rainiest months from autumn to spring – started with a bang, with a series of atmospheric rivers inspiring hope for an end to the multi-year drought. However, it ended in disappointment with low rainfall in the new year.
The sudden improvements this year were no accident – they were largely due to a global weather model floating thousands of miles away in the Arctic. This pattern is called the North American Pacific Oscillation – or PNA. It is marked by two phases: positive and negative.
In a positive PNA phase, an anticyclonic system stops offshore California and closes our storm gate. Systems that bring rain and snow are started and the condition remains dry. In the negative phase, a low pressure system sets in offshore and keeps the storm door wide open. California sees storm after storm when the pattern is negative, which has dominated since September.
Although better than last year, data released Thursday shows about 38% of the state is still in exceptional drought conditions. Central Valley regions such as Fresno that have experienced consecutive years of severe dry conditions are at risk of widespread crop loss and water shortages.
The gains seen in the Bay Area and Central Valley following recent storms are expected to continue through the remainder of the winter season. This wet pattern is likely to continue, according to the Climate Prediction Center, although La Nina conditions may still limit the amount of precipitation reaching California.
Gerry Díaz (he/they) and Yoohyun Jung are the editors of Francisco Chronicle. Email: [email protected], [email protected] Twitter @geravitywave, @yoohyun_jung