In the fall, the US state was groaning under a historic drought. The National Drought Monitor has classified 99.7 percent of the country as experiencing severe to exceptional drought. The amount of precipitation over the past three years was the lowest since measurements began. The water levels of the reservoirs, which supply the most populous US state with almost 40 million inhabitants with precious water and electricity, have fallen to alarmingly low levels in recent years.
The mega drought began in 2011 and is the worst in 1,200 years, according to a 2022 study by the University of California UCLA. In addition, there have been new heat records and enormous forest fires in recent years, which have been favored by the drought. In 2021 alone, more than 10,000 square kilometers of land burned in California, more than the area of Carinthia. Man-made climate change has intensified the drought, because with the higher temperatures, evaporation has increased and the soil and vegetation have dried out more.
With the Pineapple Express came rain
In the last few months, however, the tide has turned. A dry winter was actually predicted by the US National Weather Service’s Climate Prediction Center back in October, but things turned out differently. Much rain has poured down on California in recent months, and amazing amounts of snow have fallen on the mountains. The reason for the heavy precipitation is a weather phenomenon called “atmospheric flow”, which occurred particularly frequently this year.
An atmospheric flow is a conveyor belt in the atmosphere that is around 500 kilometers wide and several thousand kilometers long and transports moist, saturated warm air, similar to a river of water. In the case of California, the river draws moisture from the Pacific Ocean, around Hawaii. Therefore, in the USA one speaks of the “Pineapple Express”, i.e. the pineapple express. This river’s columns of steam move with the weather, driven by the jet stream that shifts highs and lows with it.
Curse and blessing
California has a climate similar to that of Mediterranean countries and owes 30 to 50 percent of its annual precipitation to a few atmospheric fluxes, according to the US National Meteorological and Oceanographic Administration NOAA. The “Pineapple Express” thus makes a decisive contribution to the water supply in California. From May to October it is usually dry and very hot. During this time, the meltwater of the Sierra Nevada feeds the snow-capped mountains, rivers and lakes, and is also of crucial importance for agriculture, especially in the Central Valley.
But the precipitation is a curse and a blessing at the same time. If they are only weak, as in previous winters, there will be extreme drought. If the rainfall is as heavy as it was this year and hits already saturated soil, it will lead to flooding, mudslides and landslides.
Power outages after storm and rain
Just like on Tuesday and Wednesday, when the tenth atmospheric flow of this winter hit California. Strong winds also knocked down many trees. Nearly 200,000 homes were without power Wednesday, many in Santa Clara County, according to poweroutage.us, which tracks power outages nationwide.
At least 27,000 people have had to evacuate their homes due to the risk of flooding and landslides, including in regions hit by wildfires in recent years. Parts of the coastal town of Montecito, which is popular with celebrities, were affected by the evacuations.
Snow records in mountains
Enormous amounts of snow have fallen in the mountains of California in recent months. The Sierra Nevada is the high mountain range that runs through California from north to south and rises up to 4,421 meters in height. It stagnates the clouds and moisture brought in from the Pacific by atmospheric flows, forcing the air to rise up the slopes. The result: the precipitation increases. During the snowfall on Wednesday alone, more than a meter of fresh snow fell in the higher areas.
In the southern Sierra Nevada there is currently two and a half times as much snow as usual and thus more than at any time since measurements have been taken. The snow cover is also significantly thicker than usual in the northern and central parts of the Sierra Nevada; the previous records from the extreme winter of 1982/1983 are also within reach here. Because for next week more heavy snowfall in the mountains and a lot of rain in the lowlands are announced.
Whole houses in locations above around 1,500 meters have already sunk in the snow, and pictures of meter-high walls of snow are making the rounds. Some ski resorts in the Sierra Nevada could be open as late as June this year, perhaps even up to July 4th, the United States National Day, California weather forecaster Ken Clark told Accuweather.
reservoirs fill up
The water levels in the state’s reservoirs were far too low until recently. Some hydroelectric power plants had to temporarily stop their work. Broad, bright rims along the shores, which are usually submerged, were visible even from space. This “bathtub ring” of lakes is now rapidly disappearing. The rains ensure that California’s reservoirs fill up again. Cachuma Lake near Santa Barbara has already reached its maximum level.
The water is also rising in the two largest reservoirs, Shasta Lake and Lake Oroville. Shasta Lake’s water level is already 100 feet higher than it was in December and is now 70 percent full, according to data from the California Water Authority. Lake Oroville has even risen by over 61 meters and is 82 percent full. The reservoirs will continue to fill up over the coming weeks and months, because the warmer season will also bring meltwater from the mountains.
Thanks to the heavy rain, strict water conservation measures will end for seven million people in southern California, according to the regional water utility Metropolitan Water District of Southern California. For the past year, parts of Los Angeles, Ventura and San Bernardino counties have had water usage restrictions due to water shortages, such as outdoor watering limited to one day per week.
Just a break from the drought?
The national drought monitor is already showing significant improvements for California, with larger parts of the state emerging from the drought every week. Some even see the end as coming, while some experts only see a pause in the drought. UCLA geographer Park Williams, the lead author of the drought study, said it was extremely unlikely that this drought would end in just one wet year.
It’s possible that California is just experiencing a pause in the 23-year mega-drought experienced in 2005, 2011, and 2017, when it also rained and snowed more than normal. Because droughts are a recurring feature of the climate in California, man-made climate change amplifies its effects. California Water Authority Director Karla Nemeth also warns that it will take more than a year for groundwater in California to begin to recover.
A climate phenomenon can also intervene in the weather from autumn: El Nino. This is a kind of gigantic air pressure swing that leads to the displacement of large masses of water in the Pacific and has global effects on the weather. In years with El Nino, California gets more rain. His opponent La Nina leads to less rain, as in the past years 2020 to 2022 in particular. Last week, the National Weather Service NOAA officially declared La Nina over.
