Sorry, you need to enable JavaScript to visit this website.

Skip to content Skip to navigation

Climate change to intensify African weather systems

Climate change could strengthen African Easterly Waves, which could in turn have consequences for rainfall in the Sahel region of northern Africa, the formation of Atlantic hurricanes, and dust transport across the Atlantic Ocean.

Ker Than
Stanford School Of Earth Sciences
April 28, 2014
Credit: NASA
african easterly waves

Weather systems that bring rainstorms to many drought-prone areas of northern Africa, carry Saharan dust across the ocean, and seed Atlantic hurricanes could grow stronger as a result of human-caused climate change, new analysis by Stanford scientists suggests.

Known as African Easterly Waves, or AEWs, these weather systems form above northern Africa during the summer season, and travel east to west, toward the Atlantic Ocean.

"Not only are AEWs important for rainfall in West Africa, they also play a role in climate across the Atlantic, including here in the United States," said Noah Diffenbaugh, associate professor of environmental Earth system science and a senior fellow at the Stanford Woods Institute for the Environment.

The climate of West Africa varies sharply from the wet tropical region along the equator to the very dry Sahara desert in the north. The strip of land that lies between these two extremes, called “the Sahel,” has experienced some of the most prolonged and severe droughts in the world over the past half century.

AEWs travel from east to west across northern Africa along two tracks. One track lies along the southern Sahel and Guinea coast region. The other track lies along the border between the northern Sahel and southern Sahara Desert. Along the northern track, the strength of the AEWs is driven largely by the difference in the surface temperature of the Sahara and the relatively cooler surface temperatures over the Sahel and Guinea Coast further south. The larger the temperature difference, the more potential energy there is for storm systems such as AEWs to draw from.


This animation shows the movement of an African Easterly Wave (AEW) across the northern Sahel region of West Africa.  Winds rotate in a counterclockwise direction around the center of the AEW (marked with the red “X”). The colors denote the amount of precipitation associated with the AEW, with blue colors representing more rainfall. Courtesy of Christopher Skinner.

The pair began by analyzing simulations from 17 different computer models of interactions between Earth's ocean and atmosphere. Each model comes from a different research institute around the world, and each one simulates physical processes in a slightly different way. "For example, all models need a component that simulates rainfall. There are multiple ways to represent rainfall in a model, and each model does it slightly differently," Skinner said.


Diffenbaugh and Skinner focused on simulations of AEWs during the period from 1980 to 2005 and simulations of AEWs during a projected future period with carbon dioxide concentrations around twice what they are today. While some of the models' differed in their simulation of AEWs during the 20th century, nearly all of them agreed that the winds associated with AEWs would grow stronger by the late-21st century if greenhouse gas emissions continue along their current trajectory.


"The temperature difference between the desert and the region further south actually becomes larger than it is today,” Skinner said. “Because the strength of the African Easterly Waves is influenced by the temperature difference between these two regions, we would expect the energy of the AEWs to become larger, and that's what the simulations show."


“This is a region that has experienced some of the most severe humanitarian disasters from droughts,” Diffenbaugh said. “But there has also been a lot of uncertainty about how global warming could impact rainfall in that region. To see such clear agreement in the response of AEWs to climate change opens the door for increasing our understanding of Sahel precipitation.”

A strengthening of waves in this region could also mean more uplift and transport of dust out of Africa and across the Atlantic. In the current climate, these dust plumes deliver life-sustaining nutrients to the ocean, but also can affect rainfall and air quality as far away as the Caribbean.

The authors also note that stronger AEWs could influence hurricanes that form in the Atlantic. The African Easterly Waves themselves don't become hurricanes, but the wave can create a protective environment inside which a lot of rainfall and vertical wind motion can develop. "This convection can serve as the seed for a hurricane," Skinner said.




Press Contact

Noah Diffenbaugh, Stanford University School of Earth Sciences: 650-223-9425,

Chris Skinner, Stanford University School of Earth Sciences: 781-264-4469,

Ker Than, Stanford University School of Earth Sciences: 650-723-9820,