When African finance and environmental ministers met last month to discuss climate-related challenges to the Millennium Development Goals, East African rains were on the agenda. Millions of Kenyans currently face food shortages as a result of successive failed rains, and periodic droughts cost the region 5-8% of GDP. A look at the climatology reveals that East Africa has been drying since the mid-1990s, but whether or not this drying is caused by climate change is still anybody’s guess.
The issue was explored by Brad Lyon at the IRI’s monthly climate briefing, held yesterday at Lamont. As Lyon explained, an EOF analysis of historical precipitation data revealed a pattern of increased rainfall over the Indian Ocean matched by drier-than-normal conditions in East Africa and eastern Australia during the March-April-May season, which generally coincides with the “long rains” in eastern Africa. This pattern explains 9% of the total variance of regional rainfall over the last 30 years; it also seems to account for the downward trend in precipitation observed in the region since the 1990s.
As Lyon tells it, some scientists take this pattern as evidence of long-term climate change. The warming of the Indian Ocean, they argue, has encouraged an increase in precipitation over the warmer water and led to a decrease in rainfall over East Africa. But while this theory is plausible, it also contradicts most of the models used by the IPCC to predict future climate change. In the long term, these models generally show wetter conditions both in East Africa and over the Indian Ocean as a result of anthropogenic forcing.
Accounting for the discrepancy between long-term climate models and recent observations is tricky. It’s possible, for instance that the recent drying is a symptom of climate change and that the IPCC’s models are unable to accurately predict precipitation in this region. One possibility for such model behavior is that they tend to generate a warming trend in the eastern tropical Pacific that has (at least thus far) not been observed. On the other hand, it may be that recent drying in East Africa is the result of decadal variability rather than long-term climate change. In this case, the EOF pattern described above would have to be understood independent of long-term climate projections in order to improve near-term climate forecasts.
Unraveling the factors that have contributed to drying in East Africa is a tricky process, but it’s not an unimportant one. If the recent drying is being driven by climate change, current models may need to be reconsidered to improve predictions. More pressing, perhaps, are the consequences that will be faced by Africa’s finance and environmental ministers – and by the people on the ground. Coping with the impacts associated with decadal variability will obviously involve different strategies than coping with impacts of long-term change.