Climate Change: Heaven for The Sa'hell'?

A recent read of mine over the weekend, by Dong and Sutton (2015), made me put down my morning cup of tea in contemplation and chew over some of the big assumptions about climate change and water in Africa. The paper essentially concludes that an observed 10% increase in seasonal average Sahelian rainfall is down to the role of increased greenhouse gas (GHG) emissions. 10% may not seem like a big increase, right? But in the semi-arid Sahel region of Africa, which was struck by devastating droughts in the 1970s and 1980s, and only receives one seasonal deluge a year (see my last post for why this is), a recovery in rainfall like this is highly significant. So, I wondered to myself, could anthropogenic climate change be beneficial for African water resources?

The semi-arid Sahel Region of Africa, coloured green (Source).

The study runs experiments with the atmospheric component of global climate models to pinpoint the cause of observed rainfall recovery. Sea surface temperatures (SSTs), GHGs and aerosols are altered together and then individually in turn. The authors found GHG forcing is the dominant cause behind recent increases in Sahelian rainfall, with 74% of simulated change responding to GHGs alone. How? Simply put, GHGs cause land to warm up more quickly than the oceans, amplifying the land-ocean temperature gradient, which intensifies the usual ITCZ cycle so that it moves slightly further north.

Precipitation changes in the Sahelian summer rainy
season, with different forcing factors applied (SST,
then both GHG & AA, then GHG only). GHGs
are found responsible for most of the changes.
(Dong and Sutton 2015)

As seems to happen more often than not these days, the media took one or two messages from the study and blew them up with twisted words, stringing together some fairly dramatic headlines, e.g. the Sunday Express, which claimed 'African Drought is OVER' and that climate change is doing what Live Aid couldn't (sorry, Bob Geldof). This isn't strictly true, and headlines like these can be very misleading. Although Dong and Sutton (2015) show average seasonal rainfall in July-September (JAS) has recently risen by 0.3mm/day relative to the 1970s-80s drought period, this does not mean climate change is bringing more rain to the entirety of Africa, nor does it mean this short-term benefit will continue to outweigh costs in the long run.

Globally, surface air temperatures are rising. We know that in a warming world, the rate of evapotranspiration increases (check my previous post for more detail). Therefore, even if there is greater rainfall in the Sahel, water won't necessarily stick around long enough for crop use or to replenish surface water supplies if it's being evaporated off as soon as it arrives. This part of Northern Africa is still very much at risk from intensified droughts in the near-future, which is unwelcome news for agriculture and famine. 

The bottom line is that studies like these shouldn't be a reason to stop tackling the issues and causes of climate change. Yes, perhaps in the short-term the Sahel will benefit from a slightly wetter wet season. But anthropogenic GHG emissions will continue to rise indefinitely over the next few decades (as stopping all emissions overnight seems as likely as pigs flying), and this will inevitably continue upsetting natural planetary systems on Earth. An accidental, transient regional benefit does not equate to a long-term global benefit. Climate change is, and will continue to, affect parts of Africa in a number of complex disparate ways. 

Dong and Sutton's study is important research, which demonstrates that anthropogenic GHG emissions already emitted are already affecting continental rainfall in a climatically sensitive area of the world. However, a robust, agreeable response from other sets of climate models will be needed to solidify such claims. Their paper reminded me that not everything you read should be taken at face value, even when it's written by highly regarded scientists. There are always more questions to ask, methods to scrutinise, and wider implications to consider. 

The book of Africa's future water supplies is still largely unwritten, with missing chapters, pages at the editing office, and uncertain conclusions. Could groundwater be a glimmer of hope in what seems like a gloomy future?

...'till next time.