Case 1: Coastal Bangladesh
Bangladesh's coastal districts face one of the most studied combinations of climate stress and population pressure in the world. 3MIP's first benchmark case asks participating modeling teams to project net internal migration in these districts from 2025 to 2050 under shared climate and socioeconomic scenarios, using shared input data.
Why Bangladesh is the first case
Three factors converge on Bangladesh. The empirical literature on internal migration there is among the densest in the climate-migration field, providing a real benchmark against which model outputs can be sanity-checked. The country's population of 175.7 million (UNFPA SWOP 2025) and its low-lying delta geography make the policy stakes consequential. And the data infrastructure — population grids, modeled migration flows, salinity layers, flood histories — is already openly licensed and usable.
The coastal districts face coastal erosion, sea-level rise, seasonal monsoons, tropical cyclones, and salinity encroachment — and their populations are highly mobile. The case was chosen for data availability and the depth of the existing literature, not because the dynamics are simple.
Bell et al. (2021) projected that migration toward Bangladesh's coast, not away from it, will continue through 2100 across the sea-level rise scenarios they studied. That finding sits in productive tension with the popular narrative of mass climate exodus and provides the empirical motivation for revisiting the problem with multiple model architectures.
The shared question
Teams choose how to operationalize "migration" within their own model architecture. The intercomparison does not require harmonized output variables; it requires harmonized inputs and a shared central question. Where outputs diverge — and they will — the synthesis paper documents the divergence and the methodological choices that drive it.
Geographic scope
The case focuses on districts in the Ganges-Brahmaputra-Meghna delta and adjacent coastal areas. The exact district list is specified in the protocol document and includes Khulna, Satkhira, Bagerhat, Barguna, Patuakhali, Pirojpur, Bhola, Noakhali, Chattogram, and adjacent inland districts that receive coastal migrants [VERIFY exact district list against protocol].
Curated input dataset
3MIP curates 16 datasets for the case — population and socioeconomic, environmental, and mobility data — documented with citations and access links on the Data page. Teams use this curation as their common input. The data list may be expanded, but any new dataset must be made known and available to all teams; contact project coordination to request the inclusion of an additional dataset.
Expected outputs and timeline
- 3MIP launches; registration opens.
- First participant webinar.
- Regular participant webinars; teams run their models and share preliminary findings.
- First synthesis at iEMSs 2026, University College Dublin (Session C7 + Workshop WSC7).
- Regular webinars continue.
- Submissions to Climatic Change topical collection, received through 2027. [VERIFY: formal Springer call not yet posted]
- Synthesis paper drafted from the collected outputs.
Background literature
The papers below frame the Bangladesh case. Bell et al. (2021) provides the direct empirical motivation; the others document the migration dynamics the participating models must contend with.
Protocol document
The 3MIP Bangladesh case protocol document specifies the shared question, the curated dataset, the climate scenarios, the geographic scope, and the output submission process. Registered participants receive the latest version of the protocol.