The Western Indian Ocean deltas

with the WIODER team

Fishing for mollusks, Incomati delta, Mozambique @IRD Stéphanie Duvail


Spatial and scenario analysis for deltas, in a context of divergent stakeholder views and land-use conflicts (Kenya, Tanzanie, Mozambique, Madagascar) and according to the submersion risks (Madagascar) 

  • Modelling of delta geosystems from data acquired in WIODER (hydrology, fishery resources, mangroves, household resilience).
  • Evaluation of areas of agreement or tensions between current uses of the territories (local production systems, public policies, private sector).
  • Comparing visions of the future of the territories (local aspirations, public policy projects, private sector projects) and building territorial prospective scenarios, sharing with the different actors and searching for consensual scenarios.
  • Conduct simulation exercises for decision-makers of the Boény Region and the city of Majunga (Madagascar) using the serious game LittoSIM and collective design of management and land-use scenarios that integrate issues related to the risks of marine submersion


Kenya, the Tana delta

Madagascar, the Bestiboka delta

Mozambique, the Incomati delta

Tanzania, the Rufiji delta

Tools and approaches

Analysis of the geosystem dynamics and deltas comparison

Participatory environmental observatories,

Land-use mapping

Forward-looking strategies

Co-construction of scenarios (LittoSIM)

Focus on Kenya

PhD defence of Peter Ng’ang’a Gitau

for the grade of Doctor in Geography of the National Museum of Natural History (ED 227, Paris, France), on the 18th of January 2023.

The defence took place at the French Institute of Research in Africa (IFRA-Nairobi), Laikipia Road, Kileleswha, Nairobi, on January 18th 2023

Focus on Mozambique

How does river flow influence the entire estuary ecosystem? 

That is the subject of the interdisciplinary delta team's research, in the Incomati Delta in southern Mozambique. The team identifies the flows needed to preserve the delta which is nursery for fish and a source of income for the local community.

The Incomati Estuary Festival, Mozambique

October 15-17, 2021, to highlight the role and functions of the estuary and its floodplains, well known to the locals but unknown to passing visitors, as well as to showcase the exceptional biodiversity of the site (it is the 2nd hotspot of biodiversity of birds in Mozambique after Gorongosa) and the expertise of local people.

The video is also available in Portuguese.

Focus on Madagascar

Alert ecological disaster in the Betsiboka delta due to the mangrove caterpillar

The attack was observed in 2020 and became massive in 2022 in the Betsiboka estuary. The culprit is a defoliator caterpillar Hyblaea puera (Cramer, 1777) that specifically attacks the mangrove tree Avicennia marina that constitutes the monospecific stand of mangroves downstream of the Betsiboka delta. 

The DiDEM/Deltas-Madagascar team was mobilised by the Boeny region to assess the situation.

> Read the article

Dialogues science and civil society, an original experiment in the Boeny region, since 2021

Two science-decision-maker dialogue workshops were held at the Roches Rouges Hotel in Mahajanga, on the theme of Mangroves, on 14-15 December 2021 and 7-8 April 2022, the third workshop in Ambato-Boeny on 24-25 May 2022 was devoted to the flooding of the Betsiboka River, and the fourth will take place in mid-September 2022 in the Marovoay region on the silting up of irrigated perimeters upstream of the Betsiboka Delta.

> Learn about this dialogue

Focus on Kenya

Poster presentation made at the 12th WIOMSA symposium, by David Ouma

October 2022

Tana River delta floodplain is maintained through a dynamic balance revolving around frequency, extent, and flooding duration. These seasonal and annual variations in flooding strongly affect the fisheries and livelihoods of the floodplain communities. In the delta, fishing is an important traditional source of livelihood, practiced alongside local agrarian livelihoods such as shifting cultivation and livestock keeping. Fishery utilization and management characteristics in the floodplain lakes of the Tana River delta are not well documented.

Livelihoods thematic scool, Tanzania, projet Wioder@Y.Lesecq


In the Western Indian Ocean, freshwater and sediment inflows and the presence of mangrove forests allow the deltas to act as a nursery for many fish species (especially shrimps, which are essential for the regional economy).

They are rapidly changing due to deforestation of upstream catchments, large-scale freshwater withdrawals for large-scale agriculture and the construction of hydroelectric dams.

The issues related to the management of deltas are complex since these are multi-actor and multi-usage zones (agriculture, fishing, livestock, agroforestry, etc.), governed locally by customary land tenure rules. Often, opposing visions of their future development collide.

They are in high demand for agro-industrial projects such as bio-fuel production, aquaculture, hydrocarbon production or mining development, while being targeted by nature conservation projects because of their abundance in biodiversity (wetlands classified as Ramsar sites, Unesco World Heritage sites, marine protected areas).

A multidisciplinary team operating in a North-South-South network developed during the WIODER project (IDRC-IRD)

4 focal points

Wanja Nyingi (Kenya), ichtyologist

Simon Mwansasu (Tanzanie), geographer

Dinis Juizo (Mozambique), hydrologist

Laurent Robison (Madagascar), hydrologist


Dominique Hervé (IRD-SENS), agronomist

Stéphanie Duvail (IRD-PALOC), geographer 


Paolo Paron (IHE Delft), geomorphologist

Olivier Hamerlynck, ecologist

Raphaëlle Ducrot (CIRAD)

Remote Sensing school, Madagascar, projet Wioder@Y.Lesecq