Atmospheric rivers are long, narrow bands of water vapour in the atmosphere that extend from the tropics to higher latitudes, acting like a pipe in the sky. These columns of vapour, typically between 250 and 375 miles wide, move with the weather and can transport up to 15 times the volume of the Mississippi River.
When atmospheric rivers make landfall, they release moisture in the form of rain or snow – and this is often a crucial contribution to water supplies. Precipitation from atmospheric rivers is thought to contribute about 20% of the Earth’s total water flow. In some regions, particularly the east and west coast of North America, south-east Asia and New Zealand, this can be more than 50%.
However, atmospheric rivers are also linked to dramatic weather events such as the torrential rain that has led to devastating flooding in southern British Columbia and north-western Washington state on Monday. This weather event was driven by an atmospheric river, known as “the Pineapple Express” that funnels warm water vapour from near Hawaii to the US west coast.
As the climate warms, an increase in air moisture means that atmospheric rivers are projected to become more intense, larger and carry higher volumes of water vapour. There is some indication that this is already happening in association with observed Pacific Ocean warming.
