Atmospheric Rivers

After the flash floods that hit parts of the United Kingdom in the last few days, UK and US scientists have suggested that such floods will be more common in the future as a result of atmospheric rivers. The suggestion comes in a report from IOP Science.

So what do scientists mean when they talk about atmospheric rivers? Think of an atmospheric river as an airborne band of moisture-laden air, which could lie about 1km high in the air and that is capable of dumping enormous amounts of water onto land below. Often an atmospheric river will begin in the tropics and move northwards, thus bringing moisture from the tropics into a storm system located in more temperate regions.

The IOP Science report says:

Atmospheric rivers (ARs) describe narrow bands (around 300 km wide and 1000s of km in length) of intense moisture flux in the lower troposphere (around 1–2.5 km in altitude) which often deliver sustained and heavy rainfall to mid-latitude regions (e.g. western North America and western Europe), with associated flooding particularly in the winter half-year (October–March)

Essentially we are discussing something like rivers in the sky. The term “atmospheric rivers” has been around since the 1990s. Atmospheric rivers are something that pose a huge flood threat on temperate, mid-latitude regions of the planet. According to Wikipedia:

a single one can carry a greater flux of water than the Earth’s largest river, the Amazon River. There are typically 3-5 of these narrow plumes present within a hemisphere at any given time.

According to The Guardian:

An example of their potential danger is the atmospheric river that caused the severe flooding on 19 November 2009 over north-west Britain. As it approached the coast it was transporting a moisture volume 4,500 times the average gauged flow of the river Thames through London.

According to the IOP Science report, climate change will mean that atmospheric rivers are going to occur more frequently and will become larger and capable of delivering even bigger quantities of prolonged rainfall. Using climate modelling, the scientists found that we could see double the amount of atmospheric rivers by the end of the century and the potential for far worse floods from each of these rainfall events is much increased. After all, a warmer atmosphere is able to carry more water and therefore deliver much higher rainfall totals.

The head of the research, Dr David Lavers, from the department of meteorology at the University of Reading says:

“The link between Atmospheric rivers (ARs) and flooding is already well established, so an increase in AR frequency is likely to lead to an increased number of heavy winter rainfall events and floods. More intense ARs are likely to lead to higher rainfall totals, and thus larger flood events.”

The report blames various recent floods in UK and north west Europe on these atmospheric rivers. Atmospheric rivers affect many temperate regions of the planet, such as UK and western Europe, the West Coast of North America and the west coast of North Africa.

Below is a video clip explaining more about Atmospheric rivers: