It rains in the American Southwest, and collects in rivers and lakes; for example, Lake Mead, which supplies Las Vegas with 90% of its water. The American Sout

It rains in the American Southwest, and collects in rivers and lakes; for example, Lake Mead, which supplies Las Vegas with 90% of its water. The American Southwest is also protected by the Earth's magnetic fields, which shield the planet from 99.9% of the radiation in space. So it's a little more complicated than that.