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Climate Change and California's Atmospheric Rivers


The atmospheric river over the Western U.S. on January 4, 2023. Photo by Lauren Dauphin / NASA Earth Observatory.

Call it what you want—a bomb cyclone, an atmospheric river, the Pineapple Express, whatever—large and intense winter storms are a regular occurrence on the North Coast. While these events are an ordinary part of our weather, they are also being made more severe and damaging by climate change.


So what is an atmospheric river? Atmospheric rivers are long, narrow bands of intense moisture in the atmosphere that can bring heavy rain and snowfall. A strong atmospheric river can carry an amount of water vapor roughly equivalent to the average flow of water at the mouth of the Mississippi River. These weather systems are responsible for most of the precipitation that California receives each year, and without them we would be unable to support nearly as much life as we currently do.

The science behind atmospheric rivers. Image from NOAA.

While atmospheric rivers are common, climate change can exacerbate their impacts and potentially increase their prevalence. As the planet warms, the atmosphere is able to hold more water vapor, leading to more intense storms and heavier precipitation. In addition, rising sea levels and the associated warming of the ocean surface can provide additional moisture for atmospheric rivers, further enhancing their intensity.

Flooding in Ferndale in Feb 2015. Photo by Ellin Beltz via Wikimedia Commons (CC BY-SA 3.0).

One of the most significant impacts of climate change on atmospheric rivers is the increased risk of flooding and landslides. As atmospheric rivers bring heavier rain and snowfall to the region, there is a higher likelihood of flooding and landslides, which can cause damage to buildings, roads, and other infrastructure, as well as loss of life.


Of particular concern are areas recently impacted by wildfire, the frequency and severity of which is also increased by climate change. As rains pound burn scars that have been stripped of vegetation by wildfires there is a lack of capacity to absorb water which leads to increased flooding. As these intense storms approach and intensify, the National Weather Service has expressed particular concerns for recently burned areas including the August Complex in Eastern Mendocino County and for the Coffee Creek Drainage area in Northern Trinity County. If you are in or near one of these recently burned areas, prepare to leave before the storm arrives and stay tuned for any possible evacuations.


In addition, flooding and landslides can also disrupt transportation and commerce, leading to economic losses. During recent storms, Highways 36, 199, and 101 were temporarily closed due to rockslides and downed power lines, and flooding closed numerous other roadways throughout Humboldt County.


Large storms often result in increased runoff, which is a good time to document impacts from industrial activities and how those activities may affect local waterways, communities, infrastructure, and property to inform timely responses if necessary. If you are in a safe location, see flash flooding, debris flows, slides or other hazards, and can safely document them, take a photo! There are several helpful apps you can download on your smartphone that will identify the GPS location as well as provide a date and time stamp for when the photo was taken, which is extremely helpful when you are trying to tell emergency responders where a particular hazard is located.

Context Cam and Avenza Maps are available for Android and iPhone.

One such app is ContextCam, which provides a GPS, time, and date stamps. Another useful app is Avenza Maps, which you can use to upload your photos onto existing maps of National Forests or one of the countless other maps that you can upload from the map store. Both of these apps use satellite technology, so you do not need cellular reception for them to be able to work. Avenza Maps will even show you your location if you are within the boundaries on a map that is already uploaded into the program.


This information can be helpful to notify emergency services of where power, communications, roads or other infrastructure may need to be repaired, or can be used to determine if anthropocentric activities such as logging or road building may have contributed to damage and if public agencies should do a site visit to ensure that best practices are being implemented and if further measures are necessary to prevent further damage or impairment.

Shasta Lake in Aug 2015. Photo by Oleg Alexandrov via Wikimedia Commons (CC BY-SA 4.0).

In addition to flooding and landslides, another impact of climate change on atmospheric rivers is the increased risk of drought. As the planet warms, the West Coast is experiencing longer and more severe droughts, even in areas that have traditionally received a high amount of precipitation from atmospheric rivers. This is partly because the increased intensity of atmospheric rivers can lead to more rapid runoff and less infiltration of water into the soil, leading to reduced long-term soil moisture and increased drought conditions. In addition, current climate science estimates that California will see longer periods without rain punctuated by more intense storms. This devastating one-two punch will dramatically affect ecosystems like ours that have evolved under more consistent conditions.


The impacts of climate change on atmospheric rivers are not limited to the West Coast. These weather phenomena have global impacts, including the potential to affect global food production and water availability. As atmospheric rivers become more intense and frequent, they can bring heavy rainfall to regions that are not equipped to handle it, leading to flooding and landslides, as well as damage to crops and other infrastructure.

The global average concentration of atmospheric carbon dioxide is 421 parts per million as of May 2022. Image by NOAA Climate.gov.

To mitigate the impacts of climate change on atmospheric rivers, it is important to address the root cause of the problem: greenhouse gas emissions. Every gallon of gas combusted in a personal vehicle, every ounce of natural gas burned to warm a house or heat a stove, and every methane burp emitted by a cow, all contribute to the global pool of greenhouse-forcing gasses in our atmosphere. We’ve already emitted enough greenhouse gasses that a certain amount of climate change is “locked in,” but every additional gram of CO2 and methane increases the severity of climate change and future storm systems.


That’s why it's incredibly important that we both reduce energy use and switch to using renewable energy wherever possible, as soon as possible. Otherwise, these storms will continue to get worse.

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