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Monday, March 4, 2013

East Africa drought in 2011 partially attributed to climate change

Scientists from the UK's Met Office have researched the causes of the 2011 East African drought and found human caused climate change was a significant contribution. The drought was a humanitarian disaster that killed an estimated 50,000 people, with 13 million in need of assistance in Somalia, Djibouti, Ethiopia and Kenya. Almost 30,000 children under the age of five were believed to have died of malnutrition in Somalia.

The drought had two components - the 'short rains' of October - November rainy season in 2010 which failed to appear, and then the absence of the 'long rains' from March - June of 2011 which really created the humanitarian crisis. The UN declared a famine on 20 July in southern Somalia, the first famine declared globally in 30 years. It was categorised as the worst drought in the region for 60 years.

Climate scientist Simon Mason from Columbia University said that East Africa has experienced a strong drying trend over the last 10 years. It is thought that rising sea surface temperatures in the Indian Ocean create conditions that pull moisture away from East Africa.

There was some debate during the drought about what role climate change played. Wikipedia discusses this on the 2011 East Africa drought page:
The head of the United States Agency for International Development, Rajiv Shah, stated that climate change contributed to the severity of the crisis. "There's no question that hotter and drier growing conditions in sub-Saharan Africa have reduced the resiliency of these communities." On the other hand, two experts with the International Livestock Research Institute suggested that it was premature to blame climate change for the drought. While there is consensus that a particularly strong La Niña contributed to the intensity of the drought, the relationship between La Niña and climate change is not well-established.

Image: The "long rains" of March - May 2011 failed over much of East Africa, leading to drought and famine (left image.) However, the "short rains" of October - December 2011 have been up to five times higher than normal, easing the East Africa drought. Image credit: NOAA Climate Prediction Center via Weather Underground

Just a few years ago saying "no single event can be attributed to climate change" was an accurate statement. And it was applied to this particular drought event. But not so any more. With extensive modelling it is possible to attribute fractional risk to climate change factors. It isn't easy and it depends on having a good collection of historical data to feed into the climate models used. And so to this current study that was published in Geophysical Research Letters: Can the 2011 East African drought be attributed to human-induced climate change?

Climate Scientists from the UK Met Office have now done an event attribution study to determine the likely causes for the drought and the failure of the rains. This is a cutting edge area of research. A decade ago no event could be positively identified as being caused by climate change. But with modern climate modelling and fractional risk attribution, some extreme weather events can now be assessed as to whether they were caused or contributed to by human caused climate change factors.

Dr. Fraser Lott, an Attribution Scientist at the Met Office and lead author on the paper, said: "We found that the particularly dry short rains in 2010 were most likely caused by natural variability. However, the chances of long rains as dry, or drier, as those of 2011 were found to have increased due to human influence."

The absence of the 'short rains' was likely caused by the strong La Niña event, the modeling found. But the 'Long rains' failure was only seen in the modelling when human climate change factors were included.

Part of the problem is the uncertainty assigned to how human influence has changed sea surface temperatures. Three different models were used to assess how the sea surface temperatures may have changed.

Initial research suggests that human influence is to blame for between 24% and 99% of the increased risk of the dry conditions seen during the long rains season of 2011. Research on refining this figure is continuing.

Dr Peter Stott, Head of Climate Monitoring and Attribution at the Met Office and co-author of the paper, said: "It is rarely possible to declare that an event is entirely caused by anthropogenic climate change and would have been impossible without it."

"This study shows that both natural causes and human influence combined to cause the East Africa Drought. In this case, while we know human influence played a role there is considerable uncertainty about just how significant this was, highlighting the complexity of attribution."

Like the Russian Heatwave of 2010, an increasing number of extreme weather events are being modelled for climate attribution. Dr Stott said: "Our aim is to understand when we can reliably estimate the odds of particular types of extreme weather events and for which types of events further improvements are required".

During August 2011 Oxfam International published a briefing paper on
Climate change and future impacts on food security
. They argued the need for developed nations to increase emission reduction goals and increasing funding for climate adaptation and building resilience in developing regions like East Africa. This would include investments in productivity of smallholder food producers by disaster risk reduction, climate change adaptation and long-term investment in livelihood protection measures and smallholder food production.

What is certain is that if we don't slash emissions and reduce fossil fuel use, temperature increases and rainfall changes in East Africa will produce another drought of equal or greater consequence affecting tens of millions of people.


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