We need to prepare for more downpours

When rain comes all at once, the impacts can be devastating, and deadly.Army National Guard Photo of Louisiana Flood Rescue

  • Two feet of rain – that is about four months’ worth – fell in parts of Louisiana over the past few days, forcing thousands to flee their homes as water rose to the rooftops. More than a dozen people have died in the flooding.
  • On July 30, nearly six inches of rain fell in two hours in Ellicott City, Md., turning Main Street into a raging river that swept away cars, tore up storefronts, and killed two people.
  • About a month earlier, up to 10 inches of rain fell in 12 hours in parts of West Virginia, causing flooding that killed 26.

Heavy downpours are expected to become more frequent in a warming world. That’s because warmer air can hold more water vapor. For each degree of warming, the air’s capacity to hold water vapor goes up by about 7 percent. An atmosphere with more moisture can produce more intense precipitation, which is what we’ve been seeing.  

Heavy downpours increased 71 percent in the Northeast and 27 percent in the Southeast between 1958 and 2012, according to the National Climate Assessment.

Last year, flash and river floods killed 176 people in the United States, more than for any other weather-related disaster.

Better infrastructure -- both “green,” like using soil and vegetation to absorb rainfall, and “gray,” using manmade materials for pipes and walls -- can give the water someplace to go other than into homes and businesses.

In urban areas, where concrete and asphalt have replaced water-absorbing soils, rain gardens and porous pavements can reduce the amount of storm water pouring through the streets, or overwhelming water treatment plants.

In other areas, more extensive storm protection infrastructure, like flood walls and storm water storage and pumping facilities, may be needed. Nashville is considering building a $110 million flood wall and pumping system after flooding in May 2010 killed 11 and caused more than $2 billion in private property damage. After initially blocking the plan, the council this summer authorized completing designs and seeking community input.

Green and gray infrastructure can even be combined. Cities like Philadelphia and Hoboken, N.J., are topping underground storm water storage tanks with recreational fields for the community.

Flood protection is costly, but so is flood cleanup. The National Oceanic and Atmospheric Administration estimates four severe floods – in Texas and Oklahoma in May 2015, South Carolina in October 2015, Texas and Louisiana in March 2016, and Houston in April 2016 – caused an estimated $7 billion in damages and killed 69 people.

More frequent and intense downpours are one of the impacts we can expect from climate change. Cities, states and businesses will need to work together to strengthen infrastructure and protect properties and lives.