Not Just W. Virginia: It’s a Hard Rain Fallin’
June 26, 2016
When I make presentations I always ask around the room whether those over 40 believe they are seeing more frequent intense precipitation. Always nods, always agreement.
One of the most rock solid predictions, and now, observations, of a changing planet.
In Kyushu, Japan on Friday, government officials urged 700,000 residents to evacuate as record heavy rains and severe flooding inundated the city for the fifth day in a row. Half a world away in West Virginia, another unpredicted record deluge dumped 8.2 inches of rain, washed out roads, cut off shopping malls, flushed burning homes down raging rivers, and left more than 14 people dead and hundreds more stranded.
Individually, these events would be odd. But taken together with what are now scores of other extreme flooding events happening around the world in the space of just a few months and the context begins to look a lot like what scientists expected to happen due to human-forced climate change.
In Kyushu, the skies opened up on Monday. An extension of a seasonal front draped across China and feeding on moisture bleeding off of record hot ocean surfaces edged out over Japan. Mountainous cloud banks unloaded. Record rains in the range of five inches an hour then began to inundate the southern Japanese island. This mass dumping of watereventually accumulated to half a meter (or 1.6 feet) over some sections of the island over the course of just one 24 hour period.
Here, NASA’s Josh Willis, interviewed in 2011, describes the effects of the last big transition from El Nino to La Nina, characterized by incredibly intense rain events.
The rains set loose raging rivers of water through Kyushu streets and saturated hillsides already weakened by an April earthquake. The flooding and resulting landslides killed 6 people on Monday alone and resulted in calls for tens of thousands of people to evacuate the hardest hit areas. Over the week, hourly rainfall totals of 1-3 inches and daily rainfall rates of 4-8 inches continued as more and more of the region succumbed to flooding. By Friday, bridges and roads had been washed out, an elderly man, a university student, and a child had gone missing, trains had been blocked by mudslides and the evacuation calls extended to include 700,000 people.
These severe flooding events add to those this week occurring in China, Australia, Sri Lanka, Indonesia, and Great Britian over just the past seven days. In addition, extreme floods have swept through Texas, Canada, Central Asia, Europe, Ghana and Argentina over the past couple of months.
The floods occur at a time when global temperatures are just coming off of new record highs during the first part of 2016. Temperatures that, in February peaked near 1.5 degrees Celsius hotter than 1880s averages. For each 1 degree Celsius that you add to global temperature, you increase the atmospheric moisture loading by about 7 percent. This is a physical fact of the Earth’s climate system. If you heat the atmosphere, you increase evaporation and that results, in turn, in more moisture held up in the world’s airs.
It’s this well understood dynamic of atmospheric physics that scientists have long warned would result in more extreme droughts and downpours as a result a human-forced warming of the world. Chris Fields, a climate scientist cited by US News and World Report in an article covering the record Paris floods earlier this month also noted:
“One of the clearest signs of climate change, over much of the world, is the increase in the fraction of the rain that falls in the heaviest events.”
So not only does a loading up of the hydrological cycle with moisture result in heavier rainfall events generally, it also results in a greater fraction of overall rainfall coming in the form of heavy rain. In other words climate change causes heavier rain on top of heavier rain. The worst events, as a result do not just get worse, they get much, much worse. And this is due to the added convection — or updrafts — that keep moisture in the air longer. In other words, the rain in a hotter world needs to be heavier to fall out of clouds that are pushed higher and with greater force by heat rising up off the Earth’s surface.