Water conservation

What La Niña means for California’s drought – The Milken Roar

As December drew to a close, rain swept across California, leaving behind a renewed vigor embraced by new growth of once gray green cover, dead hills and snow now hiding dark mountain peaks. Along with the cool feeling in the air was an almost ineffable sense of hope that California’s perpetual drought would be erased. Yet across the state, the exposed shorelines of lakes and reservoirs continue to mark water levels, reminding Californians that once the transient effects of rainfall wear off, other battles with drought will follow. loom on the horizon.

Despite a relatively wet start, with no more rain, 2021 turned out to be the driest year in a century, ending a brief respite from the drought. While this year started with desperately needed storms, California could repeat the same pattern as last year and not see any more substantial rainfall until next winter. This is because it is currently a La Niña episode, resulting in drier weather as the rain is pushed back from the coast. Additionally, as climate change progresses, rainfall highs and lows will become more extreme; big storms may seem to reverse the drought, but overall prolonged dry spells will cause it to persist. Thus, the early rains become all the more important, and California must strive to improve sustainability and conservation to get the most out of it.

Comparison of California drought on December 28 (L) and January 4, 2021 (R), revealing the impact of late December rains (Map courtesy of NDMC)

In December, downtown Los Angeles recorded 9.46 inches of precipitation, more than double the usual precipitation for this point in the hydrological year, which runs from October 1 through September 30. US Drought Watch, produced by the National Drought Mitigation Center, nearly 80% of California had extreme or exceptional drought, the two highest classifications, before the storm. Subsequently, this number was almost nil.

Importantly, much of the precipitation fell as snow, adding to the Sierra snowpack that provides 30% of California’s water. In spring, the snowpack melts and supplies water to streams and rivers to reservoirs, where it can be used during the dry summer months. During a survey in late December, the Department of Water Resources (DWR) recorded 78.5 inches of snow at Phillips Station near Lake Tahoe, double the average depth for this time of year.

Despite the positive news, DWR snow survey manager Sean De Guzman warned that the drought is not over yet. “A wet start to the year doesn’t mean this year will end above average once all is said and done.” It is already becoming obvious. After the first storms, snowfall across the state was 160 percent of average. Yet now, without much precipitation since then, the snowpack is at its normal levels for February and will decrease below typical depth if not bolstered by more precipitation.

Additionally, it is a La Niña year in the El Niño Southern Oscillation (ENSO), a recurring climate pattern that affects most of the world. That means the hotter, drier trend California is experiencing could very well be exacerbated. According to the National Oceanic and Atmospheric Administration (NOAA), during La Niña, stronger trade winds push warm equatorial Pacific waters farther west, increasing evaporation and rainfall in Southeast Asia while sinking water. air in the central Pacific. This descending air reduces the west-to-east flow of the Pacific jet stream, creating an area of ​​high pressure that diverts wet weather away from central and southern California, resulting in a drier winter.

December atmospheric river forecast from the Center for Western Weather and Water Extreme website

A wet start does not guarantee that the drought will be alleviated by the end of the year; on the contrary, the nature of California’s precipitation makes drought unpredictable, even in non-niña years. The majority of rainfall comes from large storms called atmospheric rivers (ARs), sometimes over 1,000 miles long, ARs like December storms carry immense amounts of water. In reality, Scripps Institution of Oceanography research showed that one of these extreme storms can contribute up to 25% of a region’s annual precipitation in a short period of time; 50% of Southern California’s annual rainfall arrives in just 40 hours.

As a result, without atmospheric rivers, California’s main source of precipitation, the state plunges into drought. This unpredictability is reflected in 2021, the driest year in a century. From January 26-29, 2021, the Central Coast was hit by an AR that lost 12 inches in Big Sur destroying a section of Highway 1 and closing the road for several months. The National Weather Service reported that after the rain, the Bay Area had 40% to 60% of normal precipitation for the hydrologic year. “Although it has certainly contributed to the deficit, summer is fast approaching with hopes of more rain before the dry season arrives.” He never came.

December and Seasonal Precipitation Outlook (December-January-February) (NOAA)

Last year California suffered extreme drought, and this year may be the same. About 33.6 trillion gallons of water have fallen in 2021, about half of normal precipitation, while 33.9 trillion gallons have already precipitated this year as of January 1. Even so, due to expected La Niña conditions like the high pressure area off the coast, the forecast is still not so favorable. During the dry years 2020 and 2021, a similar high pressure ridge was found, diverting wet weather from the state. In the NOAA precipitation forecast, the December forecast has been changed to reflect the atmospheric river, but overall seasonal precipitation still tends to be below average in California’s three wettest months. Just like in 2021, the state could have a big storm and nothing else for the rest of the year.

Overall, recent studies have shown that while extreme storms like atmospheric rivers will become stronger and contribute more to California’s rainfall, they will be offset by drier periods in between. Shang-Pie Xie, climatologist at the Scripps Institution Of Oceanography, analyzed the results of 16 different climate models and found that climate change enhances the effects of ENSO, increasing sea surface temperatures and atmospheric pressure response in the Pacific. Warmer oceans cause more water to evaporate, increasing air humidity and therefore the frequency of atmospheric rivers, confirming the theory that “warmer gets wetter”.

However, as the state warms and the ground dries out, more of the precipitation will fall as rain rather than snow, depleting the snowpack and decreasing the amount of water available during warmer months. ‘summer. Also, more runoff from melting snowpack will be absorbed by the ground instead of flowing into reservoirs.

It’s already becoming a problem: Depleted reservoirs have forced California to choose between providing water now or conserving for the future.

Comparison of Lake Oroville storage levels between 2020-21 and 2021-22 so far (CA DWR)

Before the December storms, the Department of Water Resources announced that the state water project would not provide water to save in the event of continued drought. With the additional rainfall, this number increased to 15%. “But the severe drought is not over. Dry conditions have already returned in January. Californians must continue to conserve as the state forecasts a third dry year,” explained DWR Director Karla Nemeth. As a result, California adopted new regulations last month, limiting unnecessary water use, such as over-watering yards, watering driveways, and watering lawns after rain, in an effort to reduce water use by Urban.

Maintaining reservoir levels should not come at the expense of other water sources. During dry years, groundwater makes up 60% of the state’s water supply, compared to 40% in typical years. This puts immense pressure on these aquifers, underground rock layers that store groundwater. Additionally, due to the prolonged drought, 63% of wells are currently operating below normal levels, many of which are at risk of drying up soon. After six years of research, DWR has approved dozens of local agency plans to improve the sustainability of their groundwater basins and manage their water supply.

This reflects a long-term goal to “make water conservation a California way of life,” improving water efficiency through legislation passed in 2018 but only beginning to be implemented. . Under this legislation, indoor water use standards will slowly decrease over time with the goal of moving closer to efficient water use, or approximately 35 gallons per capita per day. . In concert, higher standards will be enacted for agricultural use, which represents 80% of the water used in California, as well as wastewater.

People fishing in the Los Angeles River

So while California also strives to increase its water supply through recycling and desalination projects, at the end of the day what matters most is how the state and the people manage the water we have. As climate change progresses and the vagaries of the El Niño Southern Oscillation become more extreme, it is essential that we are more aware of the land we live in and our impact on its resources. Drought has become a constant in California, to the point that people are becoming increasingly indifferent to it as it persists and becomes an even bigger problem. A drop of rain can give false hope that everything is getting better, when in reality it is only an interlude if we remain passive. As California changes, we must change with it.