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Climate, Food and Water


Climate


It is widely considered that current global greenhouse emissions will lead to an increase in temperature.  The IPCC has projected that Africa will be disproportionately affected by climate change, with a rate of temperature increase 1.5x the world mean(IPCC,2012).  Current projections see Africa's temperature increasing by up to 4°C by 2100(IPCC,2012).  This will undoubtably affect rainfall in this region.  It is expected that periods of heavy rainfall will increase, while medium and low rainfall events will decrease.  This is due to the Classius Clapeyron relain, which states as temperature increases, the amount of water that can be stored in air exponentially increases (Allan,2009).  Thus, increasing temperatures in Africa will lead to increased periods of extreme rainfall.  This intensification of rainfall will be particularly pronounced in the tropics, due to higher levels of humidity as a result of ENSO flows (IPCC,2012). 


Groundwater Storage


My previous post on Groundwater shows its importance to food production in Africa. Recent studies by Taylor have suggested that Groundwater recharge occurs in periods of high annual rainfall or high monthly rainfall(Taylor,2018). Work on the Makuptaora found that in 2/3 of records between 1955-2010, no recharge occurred in the aquifer. Taylors work suggested that if rainfall is not in the top 75th percentile of total annual rainfall within the last fifty years, or seasonal rainfall is not in the 95th percentile  little or no recharge occurs.  Periods of high monthly rainfall mean difficultly in overcoming the very high levels of evapotranspiration that exist within the tropics.  Analysis of 55 years of groundwater records found that periods of highest replenishment were years of particularly strong monsoons, often caused by the Indian Ocean Dipole (IOD) and the El Niño Southern Oscillation (ENSO). This link between heavy rainfall and groundwater storage is seen across the continent, so that a shift to heavier rainfall may lead to an increase in groundwater recharge(Carter,2009). This means that groundwater irrigation will continue to constitute an attractive option for irrigation throughout Africa.   However, climate change will also increase sea levels, and this is said to threaten the quality of ground water abstracted in areas with coastal aquifers (e.g.Nile Delta), due to the increase in sea level decreasing ‘the depth of the freshwater lens through sea water intrusion’(Taylor,2009,660).  Further, groundwater recharge is dependent on soil permeability, and an increase in urbanisation may change the geology of regions, subsequently decreasing the rate at which these increased rains will be able to recharge groundwater(Wakode,2018). 




Food Crops


The majority of crop production in Africa (around 90%) is still rain-fed(Siwi,2020).  Increased variability in rainfall will lead to less consistent soil moisture levels for rainfed agriculture. This may lead to a decrease in the crop yield. Analysis of two seasons of groundnut production in India, found significant differences in yields dependent on rainfall distribution although both experienced almost the same amount of total rainfall 389 and 393 respectively(Ong,1996).  The 393mm of rainfall was distributed over twice the number of days, and the total yield of crops was over 50% more. Lighter, more frequent rainfall leads to a greater distribution of days when soil holds moisture, thus ensuring better growth.  Increase in temperature and decrease in the distribution of rainfall is expected to have negative effects on yields of many crops including cereal production, with the exception of the mountainous East African region, which will benefit from increased temperatures. One possible adaptation would be to convert  to crops more suited to the new environment, for example,cassava(IPCC,2012).



River discharge


Africa (particularly Southern Africa) already has the most varied river discharge on the planet (McMahon,2007).  Increased variability of average rainfall, and greater number of extreme precipitation events, will lead to greater variation to this rate of discharge, increasing the possibility of flooding and drought. This variation is not expected to be universal across the continent and as seen in Fig1, average discharge is expected to significantly increase in Eastern Africa, while Northern and Southern Africa are expected to see a decrease in river discharge.  Increasing variability of river discharge supports a strong argument for the use of dams, as flooding can be less catastrophic and damming provides a substantial source of water to draw from during more frequent droughts. Further, increasing temperatures are expected to accelerate the rate of glacial retreat in Africa; although recent research on the Rwenzori mountains in Uganda has found that this has very minimal effects on river discharge (Taylor,2006).  


                    

Fig 1. Projected River discharge change across Africa by 2100 (de Wit,2006) 


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