How Pacific Ocean influences long-term drought in Southwestern U.S.
The general rule of thumb had been that El Niño years — when the sea surface in a region off the coast of Peru is at least 1 degree Celsius warmer than average — tend to have more rainfall, and La Niña years, when that region is 1 degree Celsius cooler than average, tend to have less rain. But that simple rule of thumb doesn’t always hold true.