Flooding: How and Why? (credit: Meteorologist Ash Bray)

DISCUSSION: Portions of the mid-west and mid-Atlantic experienced massive flooding during the latter part of this past February. Residents in the Mid-Ohio Valley were urged to evacuate as well as prep their homes and businesses for the Ohio River’s impending invasion. Residents along the Monongahela River in West Virginia were also urged to prepare for flash flooding and possible property damage.

Flooding is among our planet’s most common – and most destructive – natural disaster. While certain areas are more prone to flooding, wherever rain falls is vulnerable. The most common flooding occurs when water inundates land that’s normally dry, usually due to river or stream beds overflowing their banks. Ice jams, excessive rain, or failed levees/dams can also irritate a river, causing it to spill out over the adjacent land (floodplain). Coastal flooding can occur due to a large storm system off the coast or even a tsunami, both of which causes sea water to rush inland.

Most floods typically take hours, sometimes days, to develop which gives residents and city management teams plenty of time to prep or evacuate. Others occur rapidly, with little to no warning. These are called “flash floods” and can be exceptionally dangerous, instantly transforming a calm creek into a massive wall of water, taking everything it its path downstream.

Experts classify floods according to their likelihood of occurring in a certain time frame. For example, “a hundred-year flood” is a large, destructive flood that in theory should be expected once every century. In all reality, this classification simply means there is a 1% chance that a flood to that magnitude could occur in any given year. Throughout the recent decades, these massive “hundred-year floods” have been occurring worldwide with unprecedented regularity.

Water, especially when moving, has awesomely destructive power. When a river spills water over its banks or the sea moves inland, poorly equipped structures cannot withstand the strength of the rushing water. Homes, bridges, cars, and other debris can be picked up and carried off. Moving water also has an erosive force, able to drag dirt from under a building’s foundation, ultimately causing it collapse.

In the United States, where severe weather prediction is advanced, floods cause upwards of $6 billion in damage and kill 140 a year. A 2007 report filed by the Organization for Economic Cooperation and Development discovered that coastal flooding alone causes nearly $3 trillion in damage worldwide.

When the floodwaters recede, it’s often that affected areas are covered in silt and mud. Occasionally the water and newly transformed landscape can be contaminated with hazardous materials such as pesticides, fuel, raw sewage, and other debris. Another potential danger is mold blooms quickly overtaking water-soaked structures. Residents of flooded areas can be left without basic necessities such as power and clean drinking water, possibly leading to outbreaks of waterborne diseases.

Flooding, especially in river floodplains, is natural and has been occurring for millions of years. Fertile floodplains like the Mississippi Valley in the Midwest, the Nile in Egypt, and the Tigris in the Middle East have been a life source for millions of years thanks to annual flooding leaving behind a plethora of nutrient-rich silt deposits behind.

Most of the destruction that comes from flooding can be attributed to society’s desire to live near coastlines and river valleys. It’s a common practice for city governments to mandate residents in flood-prone areas to purchase flood insurance and build flood-resistant structures. Massive efforts to manipulate and redirect inevitable floods have resulted in brilliant engineering efforts, including the extensive levee system in New Orleans as well as effective dikes and dams in Holland.

Scientists, meteorologists, and engineering are constantly working towards bettering our forecasting and infrastructure. Highly advanced computer modeling now allows disaster authorities and forecasters to predict with high accuracy as to where floods will occur and just how severe they could be. 

To learn more about other interesting global flooding stories and/or topics, be sure to click on the following link: www.globalweatherclimatecenter.com/flooding.

© 2018 Meteorologist Ash Bray