Fingerprinting the Role of Aerosols in Sahel Precipitation

Recent changes to rainfall in the Sahel region result from internal climate variability and in response to natural external forcings, changes in anthropogenic aerosol emissions, and increasing greenhouse gas concentrations. We exploit the different ways in which the climate system is expected to respond to different external influences, creating "fingerprints" of the Sahel rainfall response to a decrease in aerosol emissions and an increase in greenhouse gas emissions. We can differentiate between these responses by looking at spatial differences: aerosols tend to affect precipitation in the eastern and western parts of the Sahel equally, while greenhouse gases increase rainfall more in the eastern part. We can also use differences in the seasonal cycle to differentiate between increased greenhouse gases and reduced aerosols: the former depresses rainfall in the early season, the latter increases rainfall throughout the rainy season. Finally, as greenhouse gases increase, we expect to see more rainfall clustered over fewer days: in short, more intense rainfall events. Using as much information as possible in constructing these fingerprints can help us separate the influence of different factors on current Sahel precipitation. This will, in turn, help us to understand the current increase in rainfall and provide information for the future.