The Presence of Africa and Limited Soil Moisture Contribute to Future Drying of South America

Abstract

Over oceans, precipitation generally increases with warming in regions where preindustrial precipitation minus evaporation is positive. This simple “wet-get-wetter” principle does not hold over land. The Amazon region and Equatorial Africa currently receive ample rainfall, but the former is projected to dry out whereas precipitation is expected to increase over the latter. Our experiments with an idealized Atmospheric General Circulation Model and realistic continents show that land surface evaporation must be limited in order to obtain drying over the Amazon basin. Our simulations with rectangular, flat continents reveal that large parts of South America would receive more rainfall with warming in the absence of Africa. We suggest that this is due to a warming-induced Matsuno-Gill-type circulation anomaly over Africa. We propose a new simple scaling that diagnoses precipitation change from surface relative humidity ch