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hatrack

(59,436 posts)
Sat Feb 13, 2021, 10:42 AM Feb 2021

Norcal's 2-Year Rainfall Deficit 1 Of The Worst Ever; 30-70% Of Normal, No More Feb. Storms Likely

There’s a race on in California, and each day matters: the precipitation during winter that fuels the snowpack in the Sierra Nevada and fills groundwater supplies has been slow to start, and faltering at best. Northern California remains stuck in one of the worst two-year rainfall deficits seen since the 1849 Gold Rush, increasing the risk of water restrictions and potentially setting up dangerous wildfire conditions next summer. The current precipitation is only 30% to 70% of what the state would expect to have seen during a normal year – with no more big rainfall events on the horizon for February.

Precipitation in the form of rain – and snowfall at higher elevations – is critical because it refills reservoirs, packs away snow for spring runoff to feed drier parts of the state, and helps stem the risk of wildfires. It also allows California’s agriculture to continue producing important crops. This year, the state saw a very delayed start to its annual rainy season, which is typically heaviest from January to March. Wildfires sparked as late as January. It’s a sign that the window of time where rainfall and snow can add to the state’s water reserves is shrinking, says John Abatzoglou, a climatology researcher at the University of California, Merced – and that window may be even narrower in the future.

A study published this week showed that the onset of rains each fall has shifted back by a month over the past 60 years. That corresponds as well to drier fall weather, and an increase in the chance for fires to have devastating impacts, Abatzoglou says. Most of the state’s water comes from an astonishingly low number of precipitation events – just three to five winter storms do the work of building up the snowpack and filling reservoirs. That makes California uniquely vulnerable. “In years where you miss out on one or two of those, you’re probably going to struggle to get close to normal,” he notes.

EDIT

Agriculture is the state’s biggest water user, and during dry years, when surface water is less available, cities pump more groundwater – which is likely to be problematic in the coming years. “Currently, the state’s reservoirs are not as bad as they could be but the supply of groundwater – essential for agriculture – is not looking great because the majority of years in the past decade we’ve been on the dry end,” says Abatzoglou. “In the Central Valley, more and more water is being pumped for groundwater and that is not a sustainable situation. With another year of subpar precipitation, we are going to be sucking harder on that straw.”

EDIT

https://www.theguardian.com/us-news/2021/feb/11/california-dry-weather-drought-wildfire-agriculture

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