A Storm Maker T ese floods weren’t a one-time weather oddity. All over the planet, floods are causing disasters in places from Europe to China. Meteorologists are trying to figure out why. T ey start with what they know of weather


patterns. T at’s how they figured out the cause of the floods in Australia. A regular weather pattern called La Niña oſt en brings rains to Australia. T is weather pattern starts in the Pacifi c 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 warm water evaporates. Winds push the rising vapor over land. T ere, giant thunderstorms dump lots of 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 (1°F). T at may not sound like a lot. Yet it can make a big diff erence in the weather. T is tiny rise makes the ocean warmer. As a result, 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 during a rainstorm. T at may have caused the flooding in Australia. It may also be why the floods in the U. S. and Pakistan were so bad. Pakistan faced a second problem, too. T e


warm-up caused more snow and ice than normal to melt in the mountains. T e water flowed into rivers, making water levels rise. T en the rainy season began. T is time,


winds pushed the rains farther north than normal into the mountains. Giant storm clouds dumped 30 cm (12 inches) of rain in 36 hours. Already full rivers overflowed. It caused the worst flood in Pakistan’s history.


20 NATIONAL GEOGRAPHIC EXPLORER


Floods turned this sports stadium into a swimming pool.


Drying Out Weather patterns aff ect where it rains. T ey also aff ect where it doesn’t rain. T ey push rain clouds away. Some places become so dry that they have a drought. Some droughts are part of normal weather


patterns. For instance, the western U.S. typically gets little rain. Now, though, its drought has lasted three years. T at’s not normal. 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 fi re. Many meteorologists say rising temperatures


are partly to blame. T ey’re causing deadly heat waves across the planet, baking places as far north as Russia. T e intense heat evaporates moisture, even in the ground and plants. T at makes droughts worse.


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