Welcome!

Welcome to my blog on environmental change and its impacts on water in Africa!

Before we can delve into the specifics on water in Africa, we firstly need to examine the nature of environmental change that Africa is facing.

The key form of environmental change affecting Africa is that of global climate change, resulting from the enhanced greenhouse effect. Global anthropogenic activities – such as the burning of fossil fuels and the removal of natural greenhouse gas stores through deforestation – increase the quantity of greenhouse gases in the atmosphere. The greater the volume of greenhouse gases in the Earth's atmosphere, the more solar energy stored, and so a rise in greenhouse gases causes a global temperature rise. Global temperatures are currently increasing at an unprecedented rate (Figure 1), and in the past 100 years the average temperature of the Earth’s surface has increased by approximately 0.8°C (NASA 2010).

Figure 1 Land and ocean global temperature index, 1880-present (NASA GISS n/d)

How will Africa be affected?

A warmer world will have knock-on effects on the global hydrological cycle. Higher surface temperatures will increase the rate of evaporation and so hasten the drying of the land surface. Furthermore, higher temperatures increase the saturation vapour pressure of the atmosphere (i.e. the air can hold more water vapour before it falls as precipitation), which will reduce the frequency of rainfall events, but increase their intensity.

It is predicted that climate change will cause changing rainfall patterns by reducing precipitation in western and southern Africa to exacerbate drought conditions, whilst increasing precipitation in east Africa (Figure 2). The African glaciers will retreat, and overall the current stress on water availability over the continent will intensify (IPCC 2014). These impacts are already apparent; the Palmer Drought Severity Index measure of soil moisture reveals that the harshness of drought conditions in the Sahel has increased from 1900-2002 (NASA n/d).

Figure 2 Projected mean precipitation change under RCP8.5 trajectory (IPCC 2014)

However it is also important to consider the short-term environmental change that Africa faces, such as that of the El Niño Southern Oscillation.

What is the El Niño Southern Oscillation (ENSO)?

Normally in the tropical Pacific Ocean there are persistent easterly trade winds that blow from a high pressure area over the eastern Pacific to a low pressure area. The trades create upwelling that brings cold water to the surface on the west coast of South America, and this cold surface water is heated by sunlight as it is blown westward. The movement of this body of water raises sea levels in the western Pacific and lowers it in the eastern Pacific, producing a thick layer of warm water to the west.

However, every few years the surface atmospheric pressure pattern breaks down as air pressure rises over the western Pacific and falls over the eastern Pacific (Figure 3). This causes a weakening of the trade winds and they are replaced by westerly winds that bring warm surface water to the eastern Pacific. The thick layer of warm water is warmed further by the sun and halts upwelling. This warming period last for one to two years, after which atmospheric pressure rises over the eastern Pacific and falls over the western Pacific, so that the atmospheric pressure gradients return to normal (Ahrens 2012).

Figure 3 El Niño Southern Oscillation effects (Heffernan 2014)

So what does ENSO have to do with Africa?

Although the ENSO phenomenon occurs over the Pacific Ocean, the environmental impacts affecting wind and precipitation patterns are widespread and stretch to the African continent. For example, the knock-on effects of ENSO effect rainfall patterns in Lake Victoria (Mistry and Conway 2003) and increase precipitation in the wider east African region (Stager et al 2007). In addition, ENSO can intensify drought conditions in Africa, as reflected in the Sahel drought during the 1982-83 ENSO event (Ramage 1986).

Climate change and rising global temperatures are predicted to increase the frequency of extreme ENSO events (Cai et al 2015), so whilst Africa’s water situation will be affected by environmental changes over the long-term, it will also be punctuated temporarily by additional extreme conditions.

Nevertheless, although Africa's water future may look ominous due to both short and long-term impacts, the risk of water insecurity in Africa can be managed if the correct adaptation measures are adopted. This blog will explore how environmental change is having widespread impacts on water in Africa, as well as the measures taken to combat this.

Happy reading!

References:

Ahrens, C.D. (2012) Meteorology Today: An Introduction to Weather, Climate and the Environment, UK: Cengage Learning.

Cai, W., A. Santoso, G. Wang, S.W. Yeh, S.I. An, K.M. Cobb, M. Collins, E. Guilyardi, F.F. Jin, J.S. Kug, and M. Lengaigne (2015) ‘ENSO and greenhouse warming’, Nature Climate Change, 2015, 5, 849-859.

Heffernan, O. (2014) ‘Pacific Puzzle’, Nature Climate Change, 2014, 4, 167–169.

IPCC (2014) Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Geneva: IPCC.

Mistry, V.V. and D. Conway (2003) ‘Remote forcing of East African rainfall and relationships with fluctuations in levels of Lake Victoria’, International Journal of Climatology, 23, 1, 67-89.

NASA (n/d) The Water Cycle and Climate Change (online) Available at: http://earthobservatory.nasa.gov/Features/Water/page3.php (Accessed Oct 2016).

NASA Earth Observatory (2010) Fact Sheet: Global Warming (online) Available at: http://earthobservatory.nasa.gov/Features/GlobalWarming/ (Accessed Oct 2016).

NASA GISS (n/d) Global Mean Estimates based on Land and Ocean Data (image online) Available at: http://data.giss.nasa.gov/gistemp/graphs/ (Accessed Oct 2016).

Ramage, C.S. (1986) ‘El Niño’, Scientific American, 254, 76-83.

Stager, J.C., A. Ruzmaikin, D. Conway, P. Verburg and P.J. Mason (2007) ‘Sunspots, El Niño, and the levels of Lake Victoria, East Africa’, Journal of Geophysical Research: Atmospheres, 112, D15.