A version of this article first appeared on the Geology for Global Development blog, here.
Geology for Global Development (GfGD) exists to champion the role of geology in sustainable development, mobilizing and reshaping the geology community to help deliver the UN Sustainable Development Goals.
I will be contributing stories about geoscience innovations in Africa to GfGD’s blog during my time cycling in the region. This article is my first contribution.
Some landslide mitigation measures are hard to miss along Rwanda’s highways. There are gabions, and concrete drainage pathways, maintained by local women and men in fluorescent vests. Other strategies are more subtle—cassava or bean plots mixed with banana trees or ringed within a hedge 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 the nation’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.
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 leveled 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.
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 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.
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. 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 proclaimed 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 measures, 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 prioritize, 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 guidelines 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—the rest goes to response.
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.
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?