Climate Fact: La Niña and the Great Medieval Droughts
In Brief: Persistently cool conditions in the eastern tropical Pacific during the Middle Ages led to drought in the southwestern United States.
Conditions in the tropical Pacific influence weather throughout the world. On a cycle of two to seven years, the eastern tropical Pacific moves from cool (La Niña) conditions to warm (El Niño) conditions. While warm and cool conditions generally balance each other during the cycle, paleoclimate proxy data from coral reefs in the tropical Pacific indicates that this is not always the case. For much of the 14th and 15th centuries, for example, La Niñas were much more common than El Niños. La Niña conditions force storm systems to move farther north than they otherwise would be, leaving much of the northern subtropics and midlatitudes dry. This is especially true in what is today the southwestern United States. During the late Middle Ages, persistent La Niña conditions meant limited wintertime precipitation, and frequent “mega-droughts” covered much of the Southwest region.
Seasons: Winter, Spring, Summer, Fall
Source: Burgman, R et al. “Role of tropical Pacific SSTs in global medieval hydroclimate: A modeling study.” Geophysical Research Letters 37 (2010): L06705.
