Impact of Remote Anthropogenic Aerosols on East African Rainfall

East Africa has one of the world’s fastest growing populations, with rapid urbanisation. Environmental problems include land-degradation, pollution, overfishing and declining water resources, resulting in the necessity for changing livelihoods. Climate change adds to these problems, increasing vulnerability of the poorest. The impact of climate change on water resources will be critical in East Africa, but projections of the future water cycle are highly uncertain, for rainfall, lakes, rivers and groundwater. Climate projections show East Africa warming, but changes in rainfall and extremes are uncertain.

Here we explore the potential for changes in future global aerosol emissions to impact E. African rainfall. Differences in Greenhouse gas forcing remain small between scenarios over the 10-40 year time horizon. In contrast, short atmospheric lifetimes mean that changes in aerosol emissions have a potential to respond rapidly to both socio-economic and policy pathways in this same timeframe. There are already established links between aerosol changes and West African precipitation (Dong et al., 2014), however little work has been carried out to see if they also have an impact on East African precipitation.

The first stage of this work has been exploring from which remote industrial regions East African rainfall is sensitive to. We focused on 6 key high aerosol contributing regions: Europe, United States, East Asia, India, China and Northern Hemisphere Mid-Latitudes where we investigate if changes to anthropogenic aerosols (SO­₂), originating from all or any have an impact on East African rainfall both in terms of precipitation amount, spatial variation and timing.

Here we found evidence of the following:

1 All aerosol regions appear to have an impact on East African rainfall

2 Asian aerosols seem to impact (though marginally) the Long-rains

3 European, USA and Asian emissions seem to have more of an impact on the short rains

4 Aerosol reductions in all regions suggest a delay in onset of the short rains with an extension to the south of the domain into January

5 There is an indication that the short rains may become more intermittent in response to emission reductions in some regions

6 Reductions in some regions indicate the potential for a hiatus/reduction in rainfall amounts during the short rain period in November

Following this, we examine the robustness of these results by comparing with those PDRMIP model scenarios comparable to the idealised runs.