Flooding

Rivers are

Flooding

Flooding in North Carolina. Photo credit: Jody Johnson

One of the clearest changes in the weather under our warming climate has been the dramatic increase in heavy downpours and the rising risk of flooding that comes with increasingly extreme rainfall.

Around the world rainfall is being concentrated into extreme events as the atmosphere warms. In addition, regional weather patterns are shifting. In our warming climate many northern areas around the globe are being hit with a double whammy: more overall rainfall and more extreme rainfall. Normally wet areas are getting even wetter as climate change shifts global rainfall pole ward, doubling down on the threat of flooding (while many dry areas closer to the equator are getting drier as precipitation is shifted towards the planet’s poles). In the US, inland cities near large rivers are now witnessing more flooding, and this shift is consistent with the direction of climate change.

As the global average temperature increases, so too does the ability of the atmosphere to hold and dump more water when it rains. Atmospheric water vapor has been increasing. And the observed increases have been studied and formally attributed global warming.

Over the last three decades, extreme and record-breaking rainfall events have significantly increased globally, and the fingerprint of global warming has been firmly documented in this pattern. Even in dry areas what rain does fall is often concentrated into more extreme events. Climate change is now responsible for 17% of the minor extreme rainfall events we now experience, e.g. 1-in-3 year events, and it is responsible for an even greater share of the more extreme deluges, such 1-in-30 year events. Over the past century the US has witnessed a 20 percent increase in the amount of precipitation falling in the heaviest downpours. The increase in extreme precipitation has in turn increased the threat of flooding in the US.

Storms reach out and gather water vapor over regions that are 10-25 times as large as the precipitation area, thus multiplying the effect of increased atmospheric moisture. As water vapor condenses to form clouds and rain, the conversion releases heat that adds buoyancy to the air and further fuels the storm. This increases the gathering of moisture into storm clouds and further intensifies precipitation. The recent string of historic floods in the United States driven by 1-in-1,000 year rainfall is consistent with the direction of climate change on our warming planet. As our planet warms rainfall becomes more extreme and the risk of rivers flooding rises.

Just after Hurricane Matthew hit the Atlantic coast, there some flooding but people had thought the worst was over. Then the day following the rivers overloaded with runoff rushed into the small town of Fair Bluff, North Carolina, completely flooding it. This video was captured by photographer Jody Johnson.