Mountains of the Moon: Reduced riverflows?

Last week we looked at how the Rwenzori Mountain's melting glaciers are having dramatic societal and agricultural impacts. This post explores the direct effects of a reduction in glacial ice on alpine riverflow in these Ugandan Mountains, focusing on Taylor et al's (2009) paper in the Journal of African Earth Sciences. What are the effects of a warming world (and thus glacier loss - covered here) on alpine water supply?

River Mubuku, the principle river
recieving meltwater discharges at
the base of the Rwenzori Mountains.
(Source)

As covered in an earlier post, these glaciers are vital to sustaining meltwater discharges, especially during the dry season, and also act as a store of seasonal precipitation (Taylor et al 2009). Thus, concerns have arisen over potential reductions in river discharge following the recent loss of Uganda's frozen reservoir. Our understanding at present is somewhat limited due to a lack of hydrological measurements in the East African Highlands (Taylor et al 2009). Besides a few spot measurements taken by Temple in 1968, no other data exists for glacial meltwater discharges in the Rwenzoris.

By taking spot measurements of alpine riverflow along numerous altitudinal cross-sections of River Mubuku (the mountain's principal river), draining alpine icefields, Taylor et al (2009) assessed the contribution of glacial ice on the Rwenzori Mountains to river flow. Using this newly collected dataset alongside historical records, the authors found that accelerated glacial retreat since the 1960s has had minimal impact on alpine riverflow. Through their study, they conclude that meltwater from glacial ice contributes to under 2% of river flow in the Mubuku during both wet and dry seasons. So although glaciers continue to rapidly recede in the Rwenzori Mountains (see my first post in this 'mini-blog' series), it seems this is having a minor impact on alpine riverflow. River Mubuku's headwaters are provided by glacial meltwater from the Rwenzori Mountains. Thus, one may presume that due to a disproportionately high specific discharge (1730mm/year), a significant amount of riverflow originates from meltwater (Taylor et al 2009). However, this high specific discharge is actually attributed to high precipitation rates in Heath-moss and Montane forest areas (below the icefields), which occupy over 50% of the river's catchment.

The authors also argue that trivial contributions of glacial meltwaters to alpine riverflow found in the Rwenzoris may apply to similar tropical alpine regions, where glaciers contribute a small percentage of the basin area, e.g. Mount Kilimanjaro and Mount Kenya. If this is true, how is a reduction in dry season riverflow on Kilimanjaro (Desanker 2002) explained, if not due to deglaciation? Taylor et al (2009) argue this is likely to be from declining rainfall and land-use changes on the catchment (e.g. deforestation), rather than a loss of alpine glaciers.

Thoughts and reflections:

I think Taylor et al (2009)'s research is a great contribution to existing literature on this topic, and reveals that glacial recession does not impact alpine riverflow as one might initially expect. It appears that climate change's impact on the hydrological cycle (intensification and altered precipitation patterns) is more of an influence on alpine riverflow in this location than changes to alpine icefields, caused by temperature rises. However, just because glacial meltwater discharges do not have a large contribution to alpine riverflow does not mean that riverflow will not be affected in other ways by climate change in the near-future. For example, increased evapotranspiration will reduce surface water availability, and less frequent, but more intense rainfall will alter patterns of seasonal discharge in River Mubuku. All these changes, regardless of whether they result from glacial loss or through changing hydrological patterns, will have significant direct impacts on those communities who rely on water from and around the Rwenzori Mountains. Climate change is manifesting itself in a number of ways, and the impacts and consequences of this are not entirely straightforward. There is clearly a great need to increase hydrological and meteorological measurements, improving the data available for meltwater and river discharge in this area, if we are to learn more about the impact of climate change and water supply in this vulnerable part of East Africa.

I highly recommend delving into the rest of Taylor et al's paper if you're interested in this topic regarding the Rwenzori Mountains, and fancy something intellectually stimulating for a bedtime read!

Mountains of the Moon: Community consequences

Last week I introduced one of East Africa's key landscapes affected by a warming world: the snow-capped Rwenzori Mountains, supplier of lakes which feed the Nile. In this first post in this 'mini-blog' series regarding the mountains we reviewed evidence of the extent of glacial retreat due to climate change, but we have yet to cover any wider societal implications of this. How are local tribal traditions affected by this rapidly modifying environment? How are agricultural practices around the mountains expected to alter due to climate change? So, today let's take a brief step away from the physical science of the issue, and instead try to understand how changes in climate are affecting the local population.

The Bakonzo People

Bakonzo way of life will be directly impacted by warming temperatures and glacial recession. (Source)

The large-scale loss of glacial ice in the Rwenzori Mountains has significant implications for the traditional beliefs of the Bakonzo people. The Bakonzo call the mountains their home and have done for many centuries; they hold strong religious ties with this high altitude landscape (Festa 2014). Glacial ice - Nzururu - is the father of the spirits, Kitasamba and Nyabiuya, responsible for human life and fertilisation of the land (Nakileza and Taylor). For them, the mountains are literally the source of life for the surrounding land. With a dramatic loss of their father of the spirits, Nzururu, in the past century, their belief system is directly at stake (Festa 2014). Furthermore, as temperatures are rising, declining ice cover means mountain guiding treks led by the Bakonzo people (a key source of their income) are becoming more dangerous, and thus this form of tourism livelihood is at risk (Nakileza and Taylor).

Agricultural Impacts

Arabica coffee, typically found above 1400m in Uganda (Jassogne et al 2013)
(Source)

For small-scale coffee farmers, already vulnerable livelihoods are at risk in a warming world. Coffee exports are a vital part of Uganda's economy, accounting for 20-30% of foreign exchange profits (Jassogne et al 2013). However, as the climate is changing, so are the niche tolerance areas certain coffee cash crops can be grown. For example, Arabica coffee (Coffea Arabica) has a specific and small tolerance range, only able to be grown in a cool tropical climate, such as that found in the alpine regions of the Rwenzori Mountains (Jassogne et al 2013). Climate mapping by an Oxfam research team found areas suitable for growing Arabica will drastically reduce in the near future as the climate of the mountains warms. Adaptation strategies, such as using shading to cool the coffee canopies, will be wholly necessary for small-holder farmers in the Rwenzori Mountains if the Ugandan people are to mitigate negative financial impacts from rising temperatures (Jassogne et al 2013).

Shifting wildlife patterns and spread of disease

Due to rising temperatures in the mountains, there have been major changes in the altitude range of plants and animals, with some serious human repercussions. Lets use the example of mosquitoes, which carry a parasite that causes malaria. One of the mountain villages, Ibanda, is where trekkers start their hike into the Rwenzori Mountains (Festa 2014). Historically, mosquitoes have never reached this altitude, and thus residents of the village have never been affected by malaria. However, since climate change and warming atmospheric temperatures, mosquitoes can now infiltrate higher altitudes and thus malaria is becoming a more serious common problem in mountain villages like Ibanda (Festa 2014).

Thoughts and reflections

I think to truly appreciate the significance of these mountains in tropical East Africa, you have to understand the wider importance of them to surrounding communities, and ways in which climate change impacts local people and their livelihoods', as well as the more obvious impact on water supply (which I will cover in my next post). Agricultural productivity, entire livelihoods, and religious traditions are all at stake in this part of East Africa as atmospheric temperatures climb and glaciers rapidly recede.

Mountains of the Moon: A final glimpse?

The Rwenzori Mountains, which stretch across equatorial East Africa, bordering Uganda and the Democratic Republic of Congo (DRC), were described by Ptolemy in AD 150 as 'Mountains of the Moon, whose snow feeds the lakes, sources of the Nile'. Though one doesn't immediately associate ice and snow with Africa, the glaciers found on this mountain range are indeed a key source for lakes which supply the (White) Nile (Taylor 2014). But in a warming world, how will this change?

The picturesque Rwenzori Mountains (Sources: left, right)

A study in 2006 by Richard Taylor et al revealed that if current trends of glacial recession continue, there will be no more ice in the Rwenzori Mountains within the next two decades. Our changing climate has caused an estimated reduction in glacier extent across the remaining three ice-covered summits (Mounts Speke, Stanley, and Baker) from 6.5km2 in 1906, to just 1km2 in 2003. In just under a century, the areal extent covered by glaciers has declined by ~84%. Taylor further estimates a decline in ice by ~0.2 square miles per decade (Carrington 2014). That's a pretty eye-opening prediction. 

Figure from Taylor et al (2006): a) Map of Uganda, Rwenzori Mts and meteorological stations, b) "Indicator glaciers", Elena and Speke, are shown with extent in glacial cover in 1955 compared to 1990, c) Visible declines in Elena Glacier's areal extent since 1906, d) LandSat7 ETM+ satellite image from 2003, showing Mount Speke's declining glacier extents since 1906.

A stark sight: retreat of Elena Glacier's terminus in just 2 years.
(Source: Richard Taylor)

When Taylor et al (2006) set out to measure the terminal positions of both Elena and Speke valley glaciers (see figure above), they found the recession trend between 1906-1990 appeared to be continuing at alarming rates. Elena's terminus has receded by ~400m since 1906, and 140m (+-17m) since 1990 alone (Taylor et al 2006). Speke's terminal retreat is somewhat more drastic, receding ~600m since 1906, and a vast 311m since 1993 (Taylor et al 2006)! Taylor et al (2006) attribute these differences in retreat due to dissimilar supplies of ice and snow from disparate elevation and morphology. These numerical values are informative, but as the saying goes, 'a picture is worth a thousand words', and I really feel the set of photographs taken by Taylor (above right) do exactly that. In just two years, there has been an enormous visible retreat of Elena Glacier's terminus.

What has caused this deglaciation? 

It is difficult to pinpoint the exact cause of glacial retreat in the Rwenzori Mountains, due to a lack of monitored meteorological observations in the area (Taylor et al 2006). However, Taylor et al (2006) find that air temperatures on land align with warming trends. Evidence does not support the idea that increased glacial recession is due to a reduction in precipitation (in this case, snowfall) (Taylor et al 2006). Conclusively, the team suggest that the observed decline in glacial extent in the Rwenzori Mountains is due to a rapidly warming environment, amplifying ice loss through evaporation, sublimation and melting. Albedo is also a significant player. As more of the glaciers are lost, more of the darkly-coloured rock is exposed, absorbing more solar radiation and thus enhancing warming trends; a positive feedback loop develops.

These mountains, amongst other frozen reservoirs in tropical East Africa, warrant increased efforts to monitor climatic variables and glacial volume and extent in the next crucial few decades. An explicit message is being sent by the visible loss of Africa's glaciers: the climate in this region is changing, and it is changing within the time-frame of our human lifetimes.

Why are these changes important for water?

Alpine glaciers situated near the equator are a vital freshwater reservoir, storing seasonal precipitation (due to the movement of the ITCZ). They act as a buffer, sustaining meltwater flows during dry seasons (Taylor et al 2009). Thus, the fact that a warming world threatens tropical glacier existence means that usage and amount of water available from the mountains will also change. Will alpine river discharge be drastically less during the dry season if deglaciation continues? Will flooding still occur at the base of the mountains during wet seasons? How will this impact the livelihoods of those who live within and around the mountains? Is it too late to reverse or slow these changes? These are all vitally important questions which I will be covering over the next couple of posts in a series of 'mini-blogs', focusing on the Rwenzori Mountains of East Africa. 

Kili's glacial retreat: a preview

The world is beginning to wake up to some of the realities of climate change. Some of the most pristine landscapes on Earth, such as glacial peaks, are diminishing at alarming rates. We're starting to realise that the snowy, ice-covered caps existing today may not stick around to be enjoyed by our grandchildren. This threat isn't just in the high latitudes of our planet; the tropical mountain ranges of East Africa are a key location being affected by climate change.

The first video from the National Science Foundation is a great summary of some of the impacts caused by shrinking glaciers in Tanzania - the home to Mt. Kilimanjaro, part of the Eastern Rift Mountain range. Though melting/sublimating glacial ice due to climate change is a phenomenon occurring globally, increasingly significant consequences are expected in tropical mountain ranges, due to Africa's preferential warming predicted in the near future (1.5 times the global mean) (Niang et al 2014). The diminishing glaciers of Kilimanjaro have become a symbol of climate change in Africa (Thompson et al 2009). The second video is fascinating; a clip of conservationist Ian Redmond expressing his feelings towards climate change, after witnessing first-hand the vanishing glaciers on Mt. Kilimanjaro.

If you have a spare 10 minutes, make yourself comfortable and sit down with a cuppa, because I really recommend watching these.

To keep this introductory post short and sweet, I'll be drawing back to Mt. Kilimanjaro's shrinking glaciers and impacts on water at a later date. Coming up next: climate change in the Rwenzori Mountains and implications for water supply.

Groundwater: a hidden solution?

With surface water supplies becoming more unreliable in a warming world, how will Africa's increasing population and water demands be met? Perhaps we should instead look below the surface...could groundwater be the answer to Africa's current and future water problems?

In many parts of semi-arid and arid Africa, groundwater is the only reliable source of freshwater, as surface waters are ephemeral seasonally or year-round (Taylor et al 2013). A huge advantage of groundwater is that it is usually of potable quality, and is more resilient to climate variations than surface water due to its slow movement in the subsurface (Taylor et al 2009). Future climate projections highlight the disproportionate impact on Africa, whereby warming is predicted to be 1.5 times the global mean (Taylor et al 2009; Niang et al 2014). It is therefore vitally important to understand how preferential warming in Africa will impact freshwater availability. Today's post focuses on a recent study by Taylor et al (2013), which looks at evidence for groundwater dependence on heavy rainfall in the Makutapora Wellfield, Tanzania, East Africa.

This area in central Tanzania has one of the longest published records of groundwater levels in the tropics, spanning 55 years from 1955-2010. Using this record, Taylor et al (2013) discover that groundwater levels have been declining in the Makutapora Wellfield, due to increased abstraction to provide potable water to the capital, Dodoma. The removal of water from the deeply weathered granite aquifer has risen from 0.1 million m3 in the period 1955-1979, to 0.9 million m3 per month since 1990 - an increase of ~900% in half a century! How is the aquifer not depleted yet? It appears episodic recharge events are the key to sustaining intense abstraction rates...

Figure from Taylor et al (2013) demonstrating the non-linear relationship between rainfall and groundwater recharge. Shaded grey is months with "extreme" (95th percentile) rainfall, solid vertical line is the median (50th percentile), dashed line is third quartile (75th percentile).

For almost two thirds of the record, zero recharge occurs. When recharge does occur in the rest of the record, it is only under highly intense seasonal rainfall and ENSO (El Nino Southern Oscillation) events. This suggests a very non-linear relationship between rainfall and recharge events in East Africa. In a warmer world, where intensification of the hydrological cycle causes more frequent, intense precipitation events (Niang et al 2014), could replenished groundwater supplies be a viable solution for Africa's water problems? In many parts of the continent, groundwater may play a significant strategic role in the future as a way of adapting to changing surface freshwater resources (Taylor et al 2009).

The seven largest groundwater recharge events are indicated by arrows. Clear trend that El Nino years produce the largest recharge events (Taylor et al 2013).

From the figure above, we can see that 5 of the 7 major recharge events occurred during an ENSO year. For Tanzania, this extreme climate oscillation event brings additional intense rainfall and replenishes aquifers. As I'm sure you've heard in recent news stories across the globe, this Christmas our planet is set to experience one of the biggest ENSO events of the century! To date, the 1997/1998 ENSO (see graph above) was the largest event, accounting for 25% of the replenishment over the last 55 years in Taylor et al's (2013) study. With an even bigger El Nino event predicted this winter, imagine the groundwater recharge potential for the Makutapora Wellfield...

If we can improve monitoring and data collection in regions like this, it could be possible to anticipate when these huge recharge events, that sustain groundwater abstraction, will occur. Adaptive strategies may be enforced, and Africa's population might be able to enhance the water being replenished. All this only scratches the surface with groundwater in the future - what if soil infiltration capacities cannot transmit heavier rainfall events (and thus permit recharge)? What if the quality of groundwater is contaminated by pathogens from faecal runoff into open springs with intense precipitation, leaving supplies unusable? One thing seems fairly certain: in a warming world, not all of Africa's wells will run dry.

Heading East...

After a long deliberation, I've decided to narrow down the direction of this blog a tad. As you all know, Africa is an enormous continent and thus its climate is hugely varied (see my earlier post), as are the effects of climate change on water resources. For these reasons, over the remaining few months of my blogging journey, I'll be focusing purely on the climate change impacts on water resources (groundwater, surface water, rainfall, glacial melt) in East Africa.

The 12 countries included under the umbrella term of 'East Africa' according to the FAO include: Bostwana, Ethiopia, Kenya, Malawi, Swaziland, Madagascar, Mozambique, Sudan, Tanzania, Uganda, Zambia and Zimbabwe. The UN, however, also recognise Burundi, Rwanda, Djibouti, Eritrea, Somali, Comoros, Mauritius, Seychelles, Reunion, and Mayotte as part of East Africa. Quite a few countries, eh? I somehow don't think I'll be short of things to talk about in my blogging!

Most of the countries which make up East Africa (depending on political or geographical groupings), with capital cities listed. (Source)

Much of East Africa is characterised by tectonic rifting, and this largely determines the hydroclimatology of the region. For example, long, linear, deep lakes have been created due to rifting, such as Lake Malawi. This tectonic activity has also made East Africa home to Mount Kilimanjaro and Mount Kenya - two of the tallest peaks in Africa with unique equatorial glacial alpine environments. Also found in East Africa is Lake Victoria (see map below), the world's largest tropical lake, and second largest freshwater lake by surface area.

Map of the East African Rift System (EARS) showing historically active volcanoes (red triangles) and the tectonic plates involved in the rifting. (Source)

Considering its equatorial latitude, parts of East Africa are surprisingly cool and dry. The reason for this is due to a rain shadow effect experienced on the leeward side of areas of high relief (e.g. Ethiopian Highlands and Rwenzori Mountains). Lets quickly recap what a rain shadow is: warm, moist air is forced to rise up mountains/highlands, this air cools, condenses and can no longer retain its moisture, so precipitation is induced on the windward side under low pressure. As this drier, cooler air continues crossing the mountain/highland, and starts sinking on the leeward side, it warms and creates high pressure (and, thus a dry climate). Voila! This explains why parts of East Africa, such as the Horn of Africa, experience increased aridity from topographic barriers.

The rain shadow effect, commonly found in areas of high elevation in East Africa. (Source)

Just to briefly summarise what the climate change impacts are on East Africa, the wet seasons will get wetter, and the dry seasons will become drier. This rule of thumb is true for much of our understanding of generic changing precipitation patterns under climate change. In East Africa specifically, there is high confidence in a projected increase in more frequent, but sporadic, extreme precipitation events (Niang et al 2014; Seneviratne et al 2012). Overall, this equates to more intense wet seasons in the future (Niang et al 2014). 

That's all for now, folks. Next time I'll be assessing how some glacial environments in East Africa are already dramatically changing as we move into a warming world.