The majority of the West Coast’s most extreme storms have been linked to atmospheric rivers, a meteorological phenomenon in which large amounts of moisture are carried in narrow bands, often from the tropics, up to western North America. While weak atmospheric rivers are critical providers of winter rain and snow, strong events can cause extreme flooding, mudslides, and avalanches – leading to potentially catastrophic damage to life and property. A prime example: in 1996/1997, an atmospheric river event cost Northern California $1.6 billion in damages and destroyed 20,000 homes and 1,500 businesses.
WHAT: Atmospheric rivers are projected to increase in frequency and intensity as a result of climate change, with significant implications for people, infrastructure, and ecosystems. In the interior Southwest, the ecological impacts of atmospheric rivers are poorly understood. One key question is whether atmospheric rivers can alter fire patterns in this arid region by changing the amount of vegetation available as fuel. To answer this question, researchers looked at historical atmospheric river events and analyzed the subsequent changes that occurred in vegetation growth and the size of wildfires.
FINDINGS: Atmospheric rivers can increase the area burned by fires in the year following an event, particularly in the most arid parts of the interior Southwest.
Why? The heavy precipitation that atmospheric rivers bring increases soil moisture, which in turn spurs vegetation growth and temporarily inhibits fires. However, after a couple of months, the vegetation dries out and provides more fuel to feed fires than would normally be available, resulting in a larger wildfire season.
SIGNIFICANCE: Understanding how atmospheric rivers alter wildfire patterns in the Southwest is critical, particularly as the region is projected to experience more frequent and intense atmospheric river events in the future. The results of this project provide important insight into how wildfire fuel loads might change, enabling managers to better plan for future conditions and prioritize actions such as fuel load reduction following atmospheric river events.