Climate-Forecast-Based Water Level Prediction for Palau's Ngerimel Dam

The Institute of Watershed Management (IWMI) developed climate-forecast-based water level prediction technology for Palau’s Ngerimel Dam, under contract to the APEC Climate Center. The final report was delivered in July 2026.

Ngerimel Dam is a principal water source for Palau. An island nation has no alternative source to fall back on, so a falling reservoir level translates directly into supply restrictions. The difficulty is knowing in advance how much water will remain. Watching the level fall without knowing how long the dry season will last or what inflow to expect leaves few options by the time action is taken. The assignment set out to convert climate forecasts into water level outlooks and so bring response forward.

Work began with field survey and environmental data collection, establishing the actual condition of the dam and its catchment and assembling the data needed to build a prediction model. A model linking inflow to water level was then constructed and coupled to seasonal climate forecast data to produce forward-looking level outlooks. Small Pacific island catchments have sparse observational records, so data alone is not enough; conditions verified in the field form the backbone of the model.

With a level outlook available, decisions on when to begin restricting supply or to prepare alternative sources can be taken in advance. Together with IWMI’s concurrent streamflow forecasting work for the Cook Islands, the assignment transfers technology connecting seasonal climate forecasts to operational water management decisions in Pacific island states. The results can support water supply operation and drought planning in Palau.