What are atmospheric rivers? | Extreme weather conditions

Atmospheric rivers are long, narrow bands of water vapor in the atmosphere that stretch from the tropics to higher latitudes, acting like a pipe in the sky. These steam columns, typically 250 to 375 miles wide, move over time and can carry up to 15 times the volume of the Mississippi River.

When atmospheric rivers touch land, they release moisture in the form of rain or snow, which is often a crucial contribution to the water supply. It is believed that precipitation from atmospheric rivers contribute about 20% of the Earth’s total water flow. In some areas, especially the east and west coasts of North America, Southeast Asia and New Zealand, this can exceed 50%.

However, atmospheric rivers are also linked to dramatic weather events such as torrential rains that caused devastating flooding in southern British Columbia and northwestern Washington state on Monday. This meteorological event was driven by an atmospheric river, known as the “Pineapple Express,” which carries hot water vapor from near Hawaii to the west coast of the United States.

As the climate warms, an increase in air humidity means that atmospheric rivers are expected to become more intense, larger and carry higher volumes of water vapor. There are indications that this is already happening in association with observed warming in the Pacific Ocean.

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