In North Africa, some of the driest places on Earth have seen five times their average September rainfall. Flooding has affected more than 4 million people in 14 countries, according to the U.N. World Food Program. Heavy rain and floods have killed or displaced thousands and disrupted farming activities in areas where there already isn’t enough food for the population.
A northward shift in the region of clouds and rain that circles Earth near the equator is responsible for the flooding and greening. In this area, called the Intertropical Convergence Zone (ITCZ), Southern Hemisphere winds blowing from the southeast converge with Northern Hemisphere winds blowing from the northeast. The combination of converging winds, strong sun and warm ocean water leads to rising, moist air and constant clouds, showers and thunderstorms.
The movement of the ITCZ north and south of the equator during the year is primarily driven by the difference in temperature between the Northern and Southern hemispheres. It drifts toward the warmer hemisphere, which means it resides north of the equator during the Northern Hemisphere summer, usually reaching its northernmost point in August or September.
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