Melting Mountains

Mountain ecosystems are highly vulnerable to climate change, and so they can act as early warning systems for scientists of how other ecosystems are expected to be altered in the future (Kohler and Maselli 2012).

A couple of weeks ago, UNEP released a report on how climate change has impacted mountains in the East African Rift System, including Kilimanjaro. Kilimanjaro is situated in north-east Tanzania, near Kenya, and is the highest mountain in Africa (UNEP et al. 2016).

In the past 100 years Kilimanjaro has lost 80% of the glaciers strewn across its peaks, and they are expected to vanish completely within a few decades. This shrinkage is occurring as a result of rising temperatures and reduced precipitation (Kaser et al. 2004): temperatures at Kilimanjaro have increased by 0.27°C per decade (Buytaert et al. 2011), and rainfall has dropped by 39% between 1911 and 2004 (Hemp 2005).

However, although the melting of glaciers may be catastrophic from a scientific perspective as their ice layers contain priceless climate records spanning thousands of years, they actually contribute insignificant quantities to river flow and so their loss does not threaten future water supply (Taylor et al. 2009). Nevertheless, it is a stark indicator that environmental changes are occurring (Hemp 2005). Even the name ‘Kilimanjaro’ comes from the Swahili ‘Kilima Njaro’ meaning ‘shiny mountain’ in reference to the glaciers at its peak (UNEP et al. 2016), so maybe even a name change will be required once all the ice caps have melted!

But even if glacial melting is not impacting water supplies, another feature of Kilimanjaro’s changing climate does pose a threat: deforestation.

Kilimanjaro houses tropical montane forest ecosystems which amass water by collecting cloud moisture, and these act as a water source for one of Tanzania’s largest rivers, the Pangani River. Over one million people who live in the region depend on this water for irrigation and domestic use (UNEP et al. 2016).

Warmer, drier conditions due to climate change are triggering more forest fires in Kilimanjaro’s forests, and 13,000 hectares of forest have been destroyed since 1976. Several rivers have dried up as a result of the forest degradation, and this has impacted civilisation below. For example, serious water shortages have hit the town of Moshi situated in the mountain foothills, and the Chagga people living on the southern slopes are lacking water for their irrigation practices, particularly in the dry season. This will impact their food security and livelihoods, but the greatest burden will be shouldered by the women and children who will have to travel further distances to collect the water (UNEP et al. 2016). It is estimated that the reduced fog interception has caused annual dew from the forest to drop by 25%, which is equivalent to the annual water demand of the 1 million people living near Kilimanjaro. Even more worryingly, at this current rate of deforestation, it is estimated that the forest will be completely decimated within the next few years (Hemp 2005).

Therefore UNEP has called on the Tanzanian government to prioritise reforestation projects to reverse these effects and protect this vital water catchment. Such human intervention can be a powerful weapon in the fight against the threat of climate change on water supply – so let’s hope this opportunity isn’t wasted.

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.