Atmospheric river history (Part Two)

While the term "atmospheric river" didn’t exist in the 19th century, we have clear historical evidence of them causing massive disturbances. Such occurences began with the the great flood of 1862, the largest flood in the recorded history of California, Oregon, and Nevada. 

It was caused by a "family" of back-to-back atmospheric rivers that turned California's Central Valley into an inland sea. Before that, by studying tree rings and sediment layers, scientists have identified "mega-AR" events occurring as far back as A.D. 212, suggesting these have been a consistent feature of Earth's climate for millennia. 

In the last decade, our understanding has moved from "discovery" to "categorization." In 2019, Dr. F. Martin Ralph and colleagues at the Scripps Institution of Oceanography developed the AR Scale (1 to 5). Much like the hurricane scale, it helps the public understand if an incoming atmospheric river will be "beneficial" (filling reservoirs/ending droughts) or "hazardous" (causing floods and landslides). 

Overall, scientific studies confirm that atmospheric rivers are becoming stronger, wetter, larger, and more frequent in recent years, leading to more intense precipitation, and the primary reason is human-caused climate change. 

A warmer atmosphere holds more moisture, fueling these "rivers in the sky" with extra water vapor from oceans, resulting in more extreme rainfall, flooding, and wind events, particularly impacting the US West Coast. Combined with steadily increasing temperatures, this will lead to less and less snow in the US Sierras, Cascades and Rocky Mountains. 

Since I live in Park City, a mountain region, I want to know how atmospheric rivers specifically affect our snowpack and even flood risk in our mountain town compared to coastal areas and this is something we’ll discuss in our next blog, so please, stay tuned!