A Storm Maker T ese floods weren’t just a one-time weather oddity. In recent years, the weather has caused bad floods from Europe to Asia. Meteorologists are trying to figure out why. T ey discovered that a regular weather


pattern called La Niña caused the rainstorms that flooded Australia. T is weather pattern starts in the Pacific Ocean. A big patch of warm water floats there. Normally, it’s far out at sea. From time to time, though, it moves. When this warm water moves west, it sets


up conditions for La Niña in Asia. T e water is so warm that it evaporates easily. T en winds push all that vapor over nearby land. When it condenses, giant thunderstorms dump rain. T at explains the storms in Australia. Yet it


may not answer why there was so much rain. It was one of the wettest La Niña patterns ever. T e reason why may lie in Earth’s temperature.


The Heat Is On Since 1970, Earth’s temperature has risen about half a degree Celsius. T at may not sound like much of an increase, yet it can make a big diff erence in the weather. It makes the ocean even warmer. T erefore, more water evaporates and more moisture rises into the air. Today, the air holds 4 percent more water


than it did 25 years ago. T at means more rain can fall. T at may have caused the flooding in Australia, the U.S., and Pakistan. Pakistan faced a second problem, too. T ere,


warmer temperatures caused more snow and ice than normal to melt in the mountains. T is water flowed into rivers, causing them to swell. T en the rains came. High winds pushed


two big storm systems into the mountains. T ere, they collided and dumped 30 cm of rain in 36 hours. T e swollen rivers overflowed, causing the worst flood in Pakistan’s history.


20 NATIONAL GEOGRAPHIC EXTREME EXPLORER


Floods turned this sports stadium into a swimming pool.


Drying Out Weather patterns also aff ect where it doesn’t rain. T at can make some places so dry that they have a drought. Droughts oſt en are part of normal weather


patterns. T e western U.S. typically gets very little rain, for instance. Now, though, weather patterns have kept most rain clouds away a long time. Winds whip up dust storms instead of rainstorms. Grass quickly turns brown and shrivels. Dirt cracks. It’s so dry that one tiny spark can start a roaring forest fire. T e drought has lasted three years. T at’s


longer than normal. Warmer temperatures add to the problem in another way. Intense heat evaporates moisture, even in the ground and plants. So droughts become more severe.


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