126 risk maps at provincial level (one per hazard and per province), 6 national maps (one per hazard and one multi-hazard map), a risk atlas, a summary of results, an assessment of disaster risk needs and an online platform.

Five priority areas were analysed in greater detail: Bujumbura Mairie, Gitega, Rugombo (Cibitoke), Ngozi and Bukemba (Rutana).

Vulnerability relies on the 2020 DTM survey carried out on 532 collines, that is 20% of the total. Its main lesson: vulnerability is highly localised and can vary greatly between communities that are nonetheless neighbours. No area is the most vulnerable on every aspect at once.

In Ngozi, 6.75 million dollars out of 8.26 come from crops in the floodplains. The authors point out that in many countries periodic floods on agricultural plains are accepted as a natural fact by those who farm this land.

In Burundi, however, many rural households have no other livelihood. The authors leave it to the national authorities to decide, and recommend reserving protective works on these plains for exceptional cases, justified by a cost-benefit analysis.

When agricultural losses in the floodplains are removed, the communes of the north and east drop back and the west stands out. The top ten become: Muha, Ntahangwa, Mukaza, Mutimbuzi, Mpanda, Rumonge, Kanyosha, Gatara, Kayanza and Muhuta.

The authors consider this second ranking more consistent with the hazard map, and invite national experts to choose the method most useful for the future national risk management strategy.

First ranking: all hazards included. The north and east stand out, because of flooded fields. Credit: IOM Burundi, Multi-hazard risk assessment and mapping in Burundi (2020-2022), IDOM consortium, funded by the European Union.

Second ranking: without flooded fields. The west, along the lake and the Imbo plain, takes over. Credit: IOM Burundi, Multi-hazard risk assessment and mapping in Burundi (2020-2022), IDOM consortium, funded by the European Union.

1. A common geographical framework. Agree on a reference geographical framework — official names and boundaries, from collines to provinces — used by every department, and update the baseline data: boundaries, roads, built-up areas, rivers, farmland.

2. Better recording of disasters. Systematise the approach begun by the DTM in 2018: for each event, record the georeferenced location, the extent of the affected area, the intensity of the phenomenon and the damage by building type.

3. Better measuring equipment. Modernise the network of weather stations and river-flow stations, with effective maintenance programmes.

4. Planning towns and countryside. Consistent urban and rural planning is essential to avoid an uncontrolled rise in risk. It may include moving vulnerable households living in flood zones or along overflowing urban ravines to new neighbourhoods.

5. Mitigation with nature. Favour nature-based solutions, such as reforestation against landslides, involving communities in the conservation and use of the forests created.

6. Checking that each structure is worth it. Base every protective work on a sound cost-benefit analysis that validates both the investment and the risk reduction achieved.

7. Build back better. Rebuild houses and infrastructure with better materials and structures, as a priority for the most vulnerable communities who cannot be relocated.

8. Refining the values used. Have a wider group of experts review the building replacement costs and floodplain crop values used in the models.

Have local civil protection review, commune by commune, the flood zones drawn from the national map, then update the map with each new event.

Improve the management of the catchments of flood-prone rivers.

Improve local maps — geology, land use, aerial photographs — and recover the original course of streams diverted by urbanisation, an observed cause of serious damage in Bujumbura.

Extend the hydrological modelling carried out in the priority areas to other problem rivers.

Inspect bridges after every major flood: scouring at the foot of the piers, slips on the banks.

Install early-warning mechanisms along rivers, with automatic or manual gauging stations.

Update the model with detailed event records, and use existing automatic rainfall records to better understand the rains that cause damage.

Encourage the resettlement of vulnerable households living along overflowing ravines or in flat areas where water accumulates.

Set up warning systems to evacuate vulnerable residents in time, and build collective shelters in strategic locations.

Also apply most of the measures planned for torrential rain.

Help people build back better, especially households who cannot afford a wind-resistant roof.

Study the value of traditional fired-clay tiles, more common in the mountainous centre than along the lake, for better resistance to strong winds.

Adopt earthquake-resistant building codes and enforce them.

Reduce self-building: adobe and unreinforced masonry are highly vulnerable and should be strengthened, with support from trained specialists to check designs and supervise building sites.

Inventory and strengthen critical infrastructure: roads, bridges, dams, water, electricity.

Update geological maps, study active faults and carry out microzoning studies in the west of the country, where soft soils predominate.

Use the results for contingency plans and urban planning, and avoid building in high seismic-risk zones.

Limit urban development in areas highly susceptible to landslides and avoid any new housing there.

Coordinate river management to take bank erosion into account.

Limit uncontrolled deforestation and land use; reforest or plant crops that hold the soil.

Take risk zones into account when building and maintaining roads and bridges.

Clarify the gap between the flooded areas observed in Bujumbura and IGEBU’s models, check the gauge at Bujumbura port and install equivalent devices in other shoreline towns.

Review shoreline planning according to the three water levels, and revise plans as knowledge of the lake improves.

In the short term, assist affected households, including by relocation from the most exposed areas.

In the highest-risk areas, consider dykes, vegetation barriers or raised buildings, after technical, social and cost-benefit studies, while preserving the lake’s ecological balance.

Cooperate with the other lakeshore countries to understand the lake’s behaviour and build long-term joint solutions.

Information. Commune and provincial planning documents (PCDC, PCIA, SPAT) lack data on land use, hydrology and risk zones. Mapping risk zones would avoid resettling displaced people in other dangerous areas.

Warning and dissemination. An early-warning system at national and community level appears essential. IGEBU, private media and community radio stations need to disseminate information better, with simplified seasonal forecasts accompanied by concrete action messages.

Means. Lack of funding and expertise in communes, lack of protection and drainage works, need to rehearse contingency plans (stressed by the Red Cross), need for vehicles and emergency equipment.

Education. Awareness and education on risk management, and good practice in a crisis, should be spread more widely.