Geology for Global Development

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Guest Blog: Could agroforestry do more to protect Rwandans from hazardous landslides?

Megan Jamer is a geoscientist from Canada, and an avid cyclist and explorer. Megan is currently travelling around East Africa on bicycle, taking in some remarkable sites and observing first hand the relationship between geoscience and sustainable development. Today Megan makes her debut on the GfGD blog site, writing on the relationship between agroforestry, landslides, and disaster risk reduction.

Some landslide interventions are hard to miss along Rwanda’s highways. There are gabions, and concrete drainage pathways, kept unclogged by women and men in fluorescent vests. Other strategies are more subtle. Where cassava or bean plots are mixed with banana trees or ringed within a hedge, this may also reduce the damage caused by landslides in this central African nation. Rwandan agroforestry is getting attention. The strategy, which combines trees and crops in the same area, is being used to work towards the 2020 goal of trees covering thirty percent of Rwanda’s total surface area. In 2014, more than half of new seedlings distributed by the government were agroforestry or fruit varieties. Food and land scarcity pressure Rwanda’s slopes, and agroforestry is one way to address the root causes of these shortages, protecting against landslides in the process.

A rural dwelling in the hills of northern Rwanda, excavated into the slope (author’s own).

The Problem of Landslides

At least sixty-seven people were killed last year by landslides and mudslides in the north and west, and in the capital, Kigali. Deadly or not, they cause wide-ranging infrastructure damage, harming public infrastructure and trading patterns, as well as hillside settlements and agriculture. Landslides here disproportionately affect the poor, who pursue subsistence agriculture on steep slopes or live in vulnerable urban areas because they have few alternatives.

In the ‘land of a thousand hills’, slopes are made more vulnerable by rainfall patterns that some say are difficult to manage. In The New Times last year, coffee grower Pierre Munyura said that in western Rwanda“we receive about the same amount of rainfall as ever, but the rain comes in heavier and more destructive bursts.” Rainstorms are considered to be the main trigger of landslides in Rwanda, but human activities prepare the slopes for failure. They are cleared and levelled for walking pathways, homes, latrines, small plots and gardens. Other areas are hollowed out for small-scale mining. The result of these activities is a complex pattern of slope disturbance and deforestation.

Hillside communities cultivate in a manner that reflects traditional knowledge, regulations, and the resources available to them (author’s own)

Similar environmental and human conditions come together on the slopes of Mount Elgon in Uganda, where the causal factors of landslides were investigated. The researchers’ prognosis was bleak: “The growing population density not only increases the risk of damage, but hampers the search for solutions for the landslide problem as well.”  Understanding occurrence is the first step in managing rainfall-induced landslides, says Dave Petley of The Landslide Blog, and here Rwanda has made big strides. Its Ministry of Disaster Management and Refugee Affairs (MIDMAR) published a National Risk Atlas in 2015, an analysis of the earthquakes, landslides, windstorms, droughts and floods that challenge Rwanda’s resiliency. The Atlas inventories hazardous landslides, estimates slope susceptibility, and shows maps of properties that affect landslide incidence, including rainfall, slope angle, ground cover and soil characteristics.

MIDMAR’s analyses estimated that nearly half of Rwanda’s population lives in areas with moderate or high slope susceptibility to landslides. These hazards are commonly small and localized, requiring community action, but “knowledge at the citizen level [about landslides] is still low,” says Dr. Aime Tsinda, a Senior Research Fellow at the Institute of Policy Analysis and Research-Rwanda. Translating information in studies like the National Risk Atlas into local knowledge is a slow process. While it’s underway, communities are motivated to adopt agroforestry because of a hazard they are already familiar with: poor quality soil.

More Trees!

Agroforestry is the ‘intentional integration of trees and shrubs into crop and animal farming systems to create environmental, economic and social benefits’. On cultivated slopes where agroforestry isn’t practiced, small plots drape over them, resembling smooth patchwork blankets. Like blankets, their soils can more easily wash away, creep or slide catastrophically. This is what happened last year, says J.M.V. Senyanzobe, a Forestry Lecturer at the University of Rwanda. “If you observe the concerned areas,” he says, “they were empty of trees, just grasses which are not strong enough to stop the soil from being eroded.”

When trees are cut down their roots decay, eventually rendering them ineffective soil binders. The slopes of Mount Elgon demonstrate the difference. Forested areas lacked evidence of landslides, even when they grew on slope angles and in soil types that contributed to slope instability elsewhere in the study area. Deforestation began as early as 3000 BC in what was Rwanda-Urundi! Reforestation and tree cultivation have been encouraged since the 1930s and it’s working: In 1996, an FAO agroforestry study exclaimed that “photographs taken in Rwanda in the early years of this [twentieth] century show landscapes almost devoid of trees, a stark contrast to the present.

Some Rwandans are motivated to plant because of what the trees themselves offer. Bananas are brewed into beer, coffee trees have been called ‘Rwanda’s Second Sunrise’, and eucalyptus and pine provide construction materials. Other trees are valued for their structure, for example marking plot boundaries. And it’s taken some convincing, but more people are trying out types of agroforestry that plant trees and crops together, in an effort to improve soil quality. There are techniques that do more to increase soil stability. This guide recommends mimicking the plant diversity of a natural forest as much as possible, or to plant tree rows within crops along topographic contours. Within Rwanda, living hedges were found to greatly reduce soil erosion, but landslide prevention wasn’t specifically investigated. Senyanzobe recommends a combination of reforestation between cultivated areas, and agroforestry species within crop areas.  Ultimately, “the sustainable solution is to plant trees as much as possible,” he says.

Outside of agroforestry, is there a way to reduce hazardous landslides in Rwanda? Enforcing rules about how people should excavate slopes or use terracing appropriately is difficult, especially in remote areas. Similarly, mass relocation of vulnerable hillside communities is unrealistic in mainland Africa’s most densely populated country. Large-scale agroforestry interventions, by contrast, are already underway. But because they aren’t undertaken to address landslides specifically, their effectiveness is currently limited.

Pieces of the Puzzle

Speaking to the effectiveness of agroforestry for any goal, “it needs to be implemented with sensitivity to people’s needs, priorities and sociocultural and economic conditions,” says the FAO. It’s not yet clear whether many Rwandans choose tree planting specifically for reducing landslide risk—today, selling the tree’s products or increasing soil fertility are more powerful motivators. If this is how communities prioritise, then agroforestry will be pursued to the extent that those benefits are gained. The damage by landslides may be mitigated, but as a by-product.

Obstacles to agroforestry being used for disaster risk reduction overlap with the challenges of agroforestry in general. One major hurdle in Rwanda is the belief that trees can damage crops by shading them, drying them out, or otherwise competing. Unfortunately this is sometimes true. Avocado trees can harm the crops closest to them. Pine and eucalyptus trees are resilient, but also invasive.

Making the most of agroforestry involves more conversations about the risk—and prevention—of landslides. On the heels of its efforts to understand occurrence of its natural hazards, Rwanda is trying to increase public awareness of landslides in a number of ways. In the official guide to primary school construction, choosing a stable slope location is a ‘must,’ and instructions are given to this end. Public radio broadcasts, disaster committees at the district level, and discussions during monthly community service day (umuganda) on topics including disasters are other examples. Currently, about a quarter of disaster-related spending in Rwanda is directed to prevention and mitigation.

Seedling distribution on National Tree Planting Day looks pretty good, but so does a new home. Recently, several high-risk families were relocated to ‘disaster resilient’ homes in collaboration with UN-HABITAT. Both of these events received media coverage, but were largely treated as separate topics.

The collapsed downslope shoulder of a road in southern Rwanda (author’s own)

These conversations in the media and during umuganda need to continue, but hopefully soon when there’s talk of landslides in Rwanda, trees and agroforestry will be a bigger part of the discussion.

Do trees keep you safer from hazards in your environment? Do you think that any tree planting is a good thing when it comes to landslides, or can it bring mixed results?

The Impacts of Climate Change on Global Groundwater Resources (Part 4 of 4)

barry-christopherChristopher Barry is a doctoral researcher at the University of Birmingham. He has written for the GfGD Blog in the past – detailing his contribution to water projects in Burkina Faso and fundraising efforts to support such work. We have recently added a briefing note to our website, written by Christopher, describing the role of climate change on global groundwater resources. You can access the full briefing note here.

To help share the contents of this briefing note we are publishing a portion of it’s contents over a series of four blogs. This is the final instalment, with the rest available in our archives. At the end of each blog is a link to the full PDF, where you can read each section in its full context and find a full reference list.

6. Near-Surface Turbidity

6.1 How it Happens

Intense rainfall will lead to high-energy surface water.  This has the combined effect of flooding more ground due to higher river levels and picking up more material from the flooded land because of the higher energy of the water.  The material that is picked up will include sediment, but also harmful pathogens (harmful micro-organisms) that are found in excrement.  In short, much of the material on the ground is harmful for consumption and more intense water flow has a greater chance of picking this up and carrying it into the groundwater.  Turbidity of surface water has a detrimental effect on surface water and shallow groundwater.  Even when wells are covered, the effects of turbidity may be seen in shallow groundwater wells, though uncovered wells are affected more seriously.  It results from more intense wet seasons, as described in the previous section.

6.2 Threatened Areas

As this is an effect of shorter, more intense wet seasons, this is also a process to which semi-arid regions are vulnerable.  Human factors can also make a location particularly vulnerable, in particular poorly contained excrement, either from animals or humans.  Excrement placed near a drinking water source is always a hazard, but high-energy water flows make it increasingly likely that pathogens will enter the water source.  The type of water source is also important, with shallow wells, wells with improper casing and uncovered wells at the greatest risk.

6.3 Example

A study in Malawi (Pritchard et al., 2008) found that wells abstracting water from shallow groundwater were susceptible to contamination resulting from turbid water on the surface. The most serious form of contamination was microbiological, likely in many cases from nearby sites where human excrement had been dumped. Wells which were not covered at the surface consistently contained dangerous levels of pathogens, but many covered wells (about 90 % in the wet season) also failed to meet standards for safe drinking water for pathogens. Wet season results were worse than dry season and is likely to be due to intense discharge washing pathogen-carrying material into shallow groundwater. If climate change makes peak discharges more intense in the wet season, this problem is likely to worsen over time.

 

7. Parched Soil and Vegetation: Effects for Groundwater Recharge

7.1 How It Happens

The effect of climate change on the recharge of groundwater in semi-arid regions has not received enough scientific attention to be able to predict reliably.

On the one hand, longer and hotter dry seasons parches the topsoil, causing it to crack.  This actually assists the water from the next wet season in being taken into the soil and infiltrating into the groundwater, because water flowing over it ponds in the cracks, rather than flowing away and being lost into the sea.

On the other hand, the harsher dry season conditions lead to a loss of vegetation (plant life).  Vegetation helps groundwater recharge by holding rainwater in its leaves for a while before dropping it, and therefore reducing the intensity of water flow on the ground.  Tree roots also assist the infiltration of water through the soil into aquifers.

The interacting factors are depicted in Figure 3. Consequently, uncertainty exists as to what effect climate change will have on groundwater recharge with respect to surface conditions.

GWater4

Download the full briefing note (including a reference list) on the Water and Sanitation page of the GfGD website.

The Impacts of Climate Change on Global Groundwater Resources (Part 3 of 4)

barry-christopherChristopher Barry is a doctoral researcher at the University of Birmingham. He has written for the GfGD Blog in the past – detailing his contribution to water projects in Burkina Faso and fundraising efforts to support such work. We have recently added a briefing note to our website, written by Christopher, describing the role of climate change on global groundwater resources. You can access the full briefing note here.

To help share the contents of this briefing note we are publishing a portion of it’s contents over a series of four blogs. In this third instalment we focus on the effects of temperature and precipitation changes on groundwater recharge. At the end of each blog is a link to the full PDF, where you can read each section in its full context and find a full reference list.

4. Temperature Changes: Effects for Groundwater Recharge

4.1 What Happens

Groundwater recharge occurs by rainwater infiltrating through the soil.  Water at the surface will either enter the soil and groundwater, evaporate, run off into rivers and the sea, or be consumed.  The atmospheric rise in temperature increases the amount of surface water being evaporated, and therefore reduces the amount of water available for groundwater recharge.

In basins in which the groundwater is recharge from melting ice, the rise in temperature increases the rate of recharge by increasing the rate at which the ice melts.  But eventually the ice becomes depleted and then that source of water is lost.

4.2 Example

Tajikistan, in Central Asia, is a country that is highly dependent on melt water from glaciers as a source of water.  In the Pamir mountains of Tajikistan, a retreat of glaciers due to melting of 1% per year has been observed.  This raises concerns about the long-term security of this water resource.  In the short-term, increased rates of melting poses the risk of large outbursts of water.  Such an event occurred in 2005, killing 25 people (Mergili et al., 2012).

5. Precipitation Changes: Effects for Groundwater Recharge

5.1 What Happens

Climate change focuses the rainfall across the year into a shorter, more intense wet season.  In humid and temperate areas, much of the intense rain water may be wasted into the sea, because the soil has a limited capacity for infiltration.  In these areas, intense rainfall caused by climate change is likely to overwhelm the process of infiltration and therefore reduce annual groundwater recharge.

Conversely, in the arid and semi-arid climates of the sub-tropics, recharge is favoured by intense rainfall.  This is because rain water falling at a slower rate is likely to be largely evaporated.  More intense rainfall is too fast for a large proportion of rainwater to be evaporated, so a lot more of the water is able to infiltrate.

These factors are demonstrated in Figure 2.

GWater3

For basins containing ice or glaciers, the type of precipitation is also important.  Rising temperatures increase the amount of rainfall relative to snowfall.  The effect of intense rainfall is reduced if some precipitation falls as snow, because the run-off is delayed until the snow melts.  Therefore a reduction in snowfall compared to rainfall also increases the intensity of wet season run-off.

5.2 Example

In the UK, a set of climate change projections developed by the Meteorological Office called UKCP09 [1] have been used to assess the likely outcomes of changing climate on water resources.  UKCP09 consists of eleven equally likely climate scenarios projecting the next 150 years.  Simulations of river flows consistently show that we should expect a decrease in mean flow rates and even lower flows during droughts, although there is variability in the predicted results for high flow events.  Conversely, the effect on groundwater level is less pronounced – though for the UK a general decrease is more likely, some climate projections would give an increase with some groundwater models.

[1] http://ukclimateprojections.metoffice.gov.uk/21678

Download the full briefing note (including a reference list) on the Water and Sanitation page of the GfGD website. The final instalment, Part 4, will be published on this blog soon.

The Impacts of Climate Change on Global Groundwater Resources (Part 2 of 4)

barry-christopherChristopher Barry is a doctoral researcher at the University of Birmingham. He has written for the GfGD Blog in the past – detailing his contribution to water projects in Burkina Faso and fundraising efforts to support such work. We have recently added a briefing note to our website, written by Christopher, describing the role of climate change on global groundwater resources. You can access the full briefing note here.

To help share the contents of this briefing note we are publishing a portion of it’s contents over a series of four blogs. In our last blog we gave an introduction to key impacts. In this latest blog we focus on the issue of saline intrusion. At the end of each blog is a link to the full PDF, where you can read each section in its full context and find a full reference list.

3. Saline Intrusion

3.1 How it happens

Fresh (non-saline) groundwater in coastal areas forms an interface with saline groundwater under the sea.  Fresh water is less dense than saline water, so it will be found above the saline water.  Fresh water and saline water also do not tend to mix.  Both these effects are good because it means that the fresh water is easily accessible and will not be contaminated by the adjacent saline water.  The fresh groundwater discharges into the sea and may be used by humans.  It is replenished by recharge from rainfall (however indirect that may be).

This balance of input and output can be taken out of balance.  Excessive use of groundwater will increase the output, and so cause the saline-fresh water interface to move inland.  The system is also taken out of balance by a rise in sea-level, which will cause the rate of fresh water discharge into the sea to increase, until the fresh-saline water interface has moved up and inland.  As a result of this, wells drawing in freshwater near the interface may start to draw saline water (Figure 1).

GWaterBlog2

Global sea-level rise is expected as a result of melting ice near the Earth’s poles, which increases the amount of water in the sea and thermal expansion of water due to heating.  Both effects are driven by rising atmospheric temperature.  It was estimated that global average sea-level rose by about 3 cm between 1993 and 2003 (IPCC, 2008), with roughly equal contributions from melting ice and thermal expansion.

3.2 Threatened Areas

Coastal areas are the main source of concern for these effects due to the number of large cities on the coast across the world.  Large delta areas are particularly vulnerable, with large areas of flat land in danger from inundation, which, as well as many other problems, would make all the groundwater under the flooding salty.  Inland aquifers surrounded by saline aquifers may also come under threat as the freshwater recharge to them is decreased by changes in rainfall patterns and an increase in evapotranspiration (direct evaporation and evaporation from uptake through plants) of surface water.

Small oceanic islands are particularly vulnerable to saline intrusion because their freshwater lens by buoyancy and the balance between recharge and outflow.  The Ghyben-Herzberg relationship demonstrates, by considering buoyancy, that the freshwater lens will extend to a depth below sea level forty times the height by which it stands proud of sea level.  Therefore a small rise in sea level will be cause a decrease in the depth of the freshwater lens by approximately forty times its magnitude.

3.3 Examples

There is 4000 square kilometres of low-elevation land in the Nile Delta that is thought to be in danger of being submerged under the sea because of sea-level rise in the Mediterranean within this century.  All fresh groundwater resources under this area would be lost if this were to occur (Sherif and Singh, 1999).  In addition, a rise in sea-level relative to the groundwater table would cause in intrusion of saline water landward of the shore, depending on the magnitude of the rise.  A sea-level rise of 0.2 m would cause a landward intrusion of the saline-fresh water interface by about 2 km, according to the hydrogeological computer simulations of Sherif and Singh (1999).  In an inland aquifer case, Chen et al. (2004) note that regional climate change leading to reduced groundwater recharge (discussed in a later section) to a freshwater aquifer in Manitoba, Canada, could result in an intrusion of salt water from an adjacent saline aquifer because of the resulting water pressure difference.

Saline intrusion is also caused by high abstraction of groundwater for human consumption because it causes a fall in the water table relative to sea-level.  With increasing global population and strain on surface water resources, which in many ways are more sensitive to climate change than groundwater, saline intrusion caused by groundwater abstraction is likely to occur in parallel with saline intrusion caused by sea-level rise, and it is difficult to separate the separate drivers to intrusion from observations.

Download the full briefing note (including a reference list) on the Water and Sanitation page of the GfGD website. Parts 3 and 4 will be published on this blog in the coming days.

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