InTrans / Jul 28, 2021

Atmospheric rivers have major impacts on the West

Rivers in the sky with more than twice the water in the Amazon that can become fire hoses of rainfall and wind wreaking havoc on the West Coast is not the start of a climate-related thriller hitting theaters this summer.

Atmospheric rivers, as this weather phenomenon is called, are a reality for western states that can have beneficial impacts—such as replenishing water supplies in drier climates—but often have more negative impacts like decreasing the safety on roadways. They are responsible for up to half of California’s annual precipitation and can reach farther inland to the Rocky Mountains.

A recent research project led by the Center for Western Weather and Water Extremes at Scripps Institution of Oceanography sought to calculate the economic impacts of this weather phenomenon. A report summarizing the research was published by the Aurora Program.

The researchers developed a methodology that links data on atmospheric river occurrence and intensity to state department of transportation traffic flow and road safety data, and they developed a statistical analyses to quantify atmospheric rivers impacts on traffic flow and road safety outcomes. Using the methodology and analyses, the team quantified impacts on case studies on specific areas in California, Colorado, and Utah.

Some economic impact findings from the case studies included the following:

  • In California, the costs associated with atmospheric rivers-related reductions in vehicle miles traveled (VMT) on I-5 were estimated at $106 million per year, with a possible range of $67 million to $467 million per year, depending on assumptions about the sensitivity of road travel demand to the costs of VMT
  • In Colorado, using observed traffic flow rates combined with closure durations, the delay costs to passenger vehicles and trucks associated with atmospheric river-related road closures were estimated to have exceeded $1.5 million over the corridor for the month of study along a section of I-70
  • In Utah, the costs of atmospheric river-related increases in crashes were estimated to exceed $700,000 per year at four sites of study

The methodology the project team developed could be extended to estimate transportation impacts due to atmospheric rivers over wider geographic regions, including a complete national analysis.

More information about the research is available here, and a video further describing atmospheric rivers is available here.