Atmospheric flows take place at altitudes from 1,000 to 3,000 m and act like water vapor highways, transporting moisture from the tropics. Although it covers only about 10 percent of the Earth’s surface, it contains 90 percent of the water vapor that travels south. In most cases, they are fairly harmless or even beneficial, as Reed and King explain: Without atmospheric river water, drought would prevail in agriculturally important areas of Australia such as the Murray-Darling Basin.
But when atmospheric flows hit mountain ranges or hit cold fronts, they suddenly and quickly rain down stored water. Severe thunderstorms can also occur.
Warm air holds more water
Australia is now experiencing its second consecutive La Niña summer. The weather phenomenon is the counterpart to El Niño, causing the waters off the Australian Pacific coast to warm, resulting in higher humidity which then travels inland and rains. As a result, the aquifers were already well stored when the atmospheric flow spilled their wet load across the ground.
Climate change causing such a collision — and thus catastrophic flooding — is much more likely, experts at the University of Melbourne calculated using a similar flood example around Sydney last March. At the time, an atmospheric river ran over the city on the east coast, moving about 800 liters of water per second.
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