California’s wet season is officially underway, and the state is bracing for severe storms and strong winds. The latest round of storms is attributed to atmospheric rivers, systems that have played a crucial role in California’s precipitation levels for both good and bad. These rivers in the sky, as the National Oceanic and Atmospheric Administration calls them, are characterized by long streams of moisture in the atmosphere that span 250 to 375 miles wide on average.
Moisture evaporating off the Pacific Ocean and carried by weather systems from the tropics or subtropics, atmospheric rivers can carry enormous amounts of water vapor. On average, an atmospheric river carries a volume of water vapor that rivals the flow at the mouth of the mighty Mississippi River. Strong atmospheric rivers can hold more than 15 times that amount. When they make landfall, the moisture is released as rain or snow, resulting in highly destructive or beneficial storms, depending on their size, timing, and intensity.
Atmospheric rivers are essential contributors to California’s water supply, providing up to half of the state’s rainfall and snow. However, the big ones can also overload rivers and reservoirs, causing damaging floods. Moreover, strong winds accompanying these systems can take down trees and power lines, adding to their destructive tendencies.
The storms currently threatening California are part of a Pineapple Express system, which is a type of atmospheric river. Named for their origin around the Hawaiian Islands, these systems are often powerful and have been known to unleash torrential precipitation when they reach the west coast of the US and Canada. According to the National Ocean Service, they can dump as much as 5 inches of rain on California in a single day.
This week’s storms have put officials and residents on edge due to their timing and potential to wreak havoc when systems are already inundated and soils are saturated. The second storm in the set is particularly concerning, with forecasters urging residents across the state to prepare for potentially life-threatening and destructive weather.
California’s Rainy DaysDespite the potential for damage, atmospheric rivers are crucial to California’s water supply, and even the wet weather is welcomed by water officials still going the emergence from prolonged drought. Even with the wet weather, California’s snowpack is lagging this year, and there is hope that a heavy dusting could get it closer to historic averages by the end of the wet season in April.
The climate crisis is playing a significant role, with models showing these shifts will occur with increasing intensity as the world warms. As ocean temperatures rise, atmospheric rivers are expected to become more severe, adding more risks for floods across California and the west. Moreover, as temperatures rise, precipitation is more likely to fall as rain rather than snow, posing problems for the state’s water supply.
Governor Gavin Newsom has declared a state of emergency for eight counties in southern California in response to the recent storms. The declaration helps mobilize resources to impacted areas and authorizes the California National Guard to be deployed as needed. It also streamlines the process for utility providers and out-of-state contractors to come in for repairs during and after the storm, ensuring a smoother recovery.
As California navigates these precarious weather conditions, residents and officials are bracing for the worst while also acknowledging the essential role atmospheric rivers play in the state’s water supply. With the climate crisis looming, it is crucial that the state prepares for the consequences of a catastrophic megaflood, which could displace millions and generate over $1 trillion in losses.