Leveraging Open Data, Open-Source Tools, and Interoperable Web Services for Transboundary Hydrological Climate Services in the Sahel

Accessibility, interoperability, and sustained availability of hydrological and climatological data are critical for effective climate services. This is especially true in regions where data scarcity and operational challenges limit the development of sustainable early warning systems.

Building on this need, this work presents an open-source, interoperable hydrological web platform designed to support National Meteorological and Hydrological Services (NMHSs) in the Sahel. The SLAPIS (Système Local d’Alerte Précoce contre les Inondations de la Sirba) web platform, first developed in Niger, has evolved into SLAPIS Sahel, a transboundary hydrological climate service jointly implemented in Niger and Burkina Faso. The system provides the access, processing, and dissemination of near-real-time observations and hydrological forecasts through standardised web services and APIs, fostering data reuse and integration into operational Flood Early Warning Systems (FEWS). This evolution enables authorities in both countries to address cross-border flood risks, coordinate responses, and access consistent data for regional planning and flood management.

The use of interoperable services and automated data pipelines allows seamless integration of multiple data sources and facilitates the delivery of user-oriented hydrological services.

The system integrates ground observations and interoperates via APIs with existing large-scale hydrological forecasting platforms, including GloFAS 4.0, HYPE-based models, and others whose integration is currently being finalised.  Automated pipelines ingest these diverse data sources by standardising their formats and timing into a single, locally useful layer. Data pipelines are written in Python and run without manual intervention. The web front-end uses Leaflet.js for interactive mapping and vanilla JavaScript for real-time chart rendering. Processed data sets are available through a customised CKAN-based catalogue and exposed via RESTful APIs in CSV, JSON, GeoJSON, and OGC-compliant WFS formats. The lightweight architecture enables low-cost deployment and maintenance, which is vital for sustainability in resource-constrained settings. The platform uses only open-source libraries, with no proprietary components.

The platform's core feature is impact-based flood forecasting. It compares forecasted discharge with locally defined thresholds—derived from hydraulic simulations and fieldwork—to generate flood scenarios and hydrological information on 11 localities. Next, hydrometeorological data are linked to these thresholds, flood-prone areas, and associated impacts. As a result, NMHSs can assess the hydrological situation, view forecasts and historical data sets, and download relevant datasets. This improves the relevance of information for decision-making and risk management.

The deployment of SLAPIS Sahel in the Sirba River basin exemplifies how open, interoperable data services and collaborative development directly reinforce sustainable, cross-border hydrological service delivery. Furthermore, sharing ground observations strengthens model calibration and provides the local data needed to refine flood thresholds. This approach is easily replicable: the same pipeline architecture can integrate forecasts from various global hydrological models, making it applicable even in basins where local models are not available.