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California, ‘America’s garden,’ is drying out

Posted on 10 June 2021 by dana1981

This is a re-post from Yale Climate Connections

California, along with much of the rest of the western United States, is once again mired in drought. In fact, California has experienced significant drought conditions in 13 of the 22 years (60%) since the turn of the century.

A 2020 study in the journal Science concluded that 2000 through 2018 was the second-driest 19-year period in the U.S. Southwest in at least the past 1,200 years, and a 2014 paper in Geophysical Research Letters found that 2012 through 2014 was the driest three-year period in California over that same timeframe.

Nearly the entire state is currently in the ‘severe’ drought category or worse, and three-quarters is experiencing ‘extreme’ to ‘exceptional’ drought, according to the U.S. Drought Monitor.

The consequences of drought in California are felt well outside the state’s borders. California is effectively America’s garden – it produces two-thirds of all fruits and nuts grown in the U.S. The state’s agricultural industry generates $50 billion each year, which is more than the entire gross domestic products of Vermont and Wyoming, and as large as the economy of Alaska or Montana. California produces nearly all of the almonds, artichokes, avocados, broccoli, carrots, celery, kiwi, figs, garlic, grapes, raisins, raspberries, strawberries, honeydew melons, nectarines, olives, pistachios, plums, tangerines, mandarins, and walnuts grown in the U.S. About 80% of all almonds in the world are grown in California: The state’s almonds alone generate $6 billion annually. But nut trees are water-intensive (though notably less so than the alfalfa and pastureland grown for animal agriculture), and unlike seasonal crops, they cannot be fallowed in a dry year. Given the lack of water in 2021, some farmers have been forced to resort to tearing out valuable almond trees and instead planting less thirsty crops.

About 80% of the state’s developed water use goes to the agriculture industry, so anyone who enjoys eating fruits and nuts should be concerned that climate change is increasing the odds of megadroughts permanently drying California.

Changing climate is supercharging southwestern droughts

According to the 2020 study in Science cited earlier, human-caused climate change made southwestern drought conditions between 2000 and 2018 about 46% more intense than they would have been naturally, “pushing an otherwise moderate drought onto a trajectory comparable to the worst [U.S. southwest] megadroughts since 800 CE,” the heyday of the Mayan civilization.

It’s not just California; 96% of the western U.S. is currently experiencing drought conditions, including the entire states of Oregon, Nevada, Arizona, Utah, and New Mexico. The drought conditions led Utah Governor Spencer Cox recently to urge the state’s residents of all faiths to hold a “weekend of prayer” for rain.

Different kinds of drought

There are several different kinds of drought, all worsened by human activity. Dwindling soil moisture is known as “agricultural drought,” and is exacerbated by the increased evaporation and transfer of moisture from land to the atmosphere that comes about in a warming climate.

A lack of rain and snow is called “meteorological drought.” A 2018 study in Nature Climate Change used climate models to predict that California’s precipitation patterns will shift in a hotter world, with more rain falling in the winter but less in spring and fall months, lengthening the state’s dry season. This prediction was borne out in a 2021 study published in Geophysical Research Letters, with researchers finding that “the precipitation season has become shorter and sharper in California” since the 1960s.

“Snow drought” also plays a key role in California, 30% of whose water supply originates from the snowpack in the Sierra Nevada mountains. As temperatures rise, more precipitation falls as rain and less as snow, and the snowpack melts more quickly in the late spring and early summer. A 2018 study in Geophysical Research Letters estimated that global warming has already shrunk the Sierra Nevada snowpack by about 20% and increased early-season runoff by 30%, and that each additional degree Celsius of warming will shrink the snowpack by about another 20%.

Snow drought in California can then lead to “hydrological drought,” when water levels fall in rivers, lakes, and streams. In June 2021, California’s reservoir water levels were about 40% below the historical average, and the snowpack was completely gone more than a month earlier than normal.

Extensive drought damages felt widely

In addition to its adverse impact on California agriculture, drought results in damaged forests, worse wildfires, reduced hydroelectricity generation, stressed fish populations, and depleted groundwater aquifers. According to the Fourth National Climate Assessment Report, the combination of worsening droughts and expanding bark beetle populations due to warming winters killed 7% of the western U.S. forest area over the past four decades.

The hotter and drier conditions during most of the year, combined with the dead trees, have created more fuel for wildfires, which the report concluded have burned twice as much area in the southwestern states over the past three decades as would have burned in the absence of human-caused climate change. The smoke from those wildfires is dangerously unhealthy to breathe, and in the record-shattering 2020 fire season, the wildfire smoke spread all the way to the U.S. east coast.

That same report found also that the severe drought between 2011 and 2015 reduced hydroelectricity generation in California by two-thirds. The water level in Lake Mead, the reservoir formed by Hoover Dam near Las Vegas, has fallen by 130 feet to its lowest level since its creation in 1936, and the reservoir has lost 60% of its water volume since 2000. As the National Assessment Report concluded, “The reduction of Lake Mead increases the risk of water shortages across much of the Southwest and reduces energy generation at the Hoover Dam hydroelectric plant.”

The lack of surface water also threatens salmon and other fish species in California rivers. And it forces farmers to pump more water from groundwater aquifers, which leads to land subsidence that also stresses infrastructure.

As water resources experts at the Pacific Institute wrote earlier this month, there are steps that southwestern states can take to mitigate drought impacts, “including changes in the efficiency of urban and agricultural water uses, the expansion of non-traditional water sources like stormwater and recycled water, and voluntary changes in behavior.” Curbing greenhouse gas emissions from fossil fuels is of course the most important measure to lessen the threat of megadroughts in the future and their impacts on one of America’s key food-producing states.

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Comments 1 to 2:

  1. Does someone think about the origin of the humidity which forms the rains in California and all America, up to Greenland, Scandinavia and hole Europe? This is no Joke! - Look at the stratospheric and climate occurance over the carribian see. There is always coming some humidity from the pacific, mixing up with the humidity of two mighty vapor producers, the Amazon and the Orinoco basins. I have no doupt, that if we want to bring rain to America's gardens, we should inhance Amazonia's evapotranspiration.

    Actually lots of the floodable forests, Várzea and Igapó are severely desturbed. Especially during the dry season in the Amazon, this leeds to a severe vapor-deficit in the upper layers of the atmosfere. As a consequence, there is savannization of the nonflooded forests and drought in the northern and southern hemispheres, which depend on that moisture.

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  2. sfkeppler:

    Virtually every land surface receives a portion of the water that falls on it as precipitation from the oceans. How do I know this? Virtually every land surface has streams and rivers that eventually return water to the oceans, and the only way for it to get back from the oceans to the land is for it to evaporate from the oceans and get transported through the atmosphere back over the land.

    The processes that control this are the weather and hydrological cycle.

    For the specifics in your question: California gets much of its water from the Pacific Ocean. A lot less Pacific Ocean moisture reaches far inland, though, due to the west coast mountains. For much of the U.S. east of the mountains, the Gulf of Mexico and the Atlantic Ocean are major sources. Further north, into Canada (especialy the mid-west), you start to see some moisture that finds its way from the Pacific, across Alaska, and then back down into the continental areas.

    For the Amazon (and any oher forests), as long as there are streams and rivers draining to the ocean, they will be getting more in preciptation than they are losing by evaporation.

    In Europe, much comes from the Atlantic Ocean. Asia? Look to the Indian Ocean for central areas, and the Pacific for eastern areas.

    Exact pattern vary with daily and seasonal weather patterns, but there are some dominant consistent patterns. There is an interesting animation on this page:

    and that same resource has good information on the hydrological cycle in general.

    A nice image of the dominant patterns is in this Wikipedia image:

    Here is a smaller version of the image:

    Global Circulation


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