Satellite and in situ information for flood early warning and hydropower dam reservoir management

The TEMBO Africa Flood Early Warning Service (FEWS) is designed to enhance community safety by providing timely alerts about impending extreme weather events. The TEMBO Africa hydropower dam reservoir management service provides water authorities with near-real time information to optimize operations and dam safety. These services are based on the use of free and open satellite information and data from cost-effective sensors and innovative applications that are developed by TEMBO Africa partners.

Optimal solutions for improving water management services in Africa must be inexpensive, low-complexity and take advantage of the available resources. Using revenue generated by project-produced services, TEMBO Africa aims to make hydro-meteorological data in Africa freely and openly available. TEMBO Africa, which stands for Transformative Environmental Monitoring to Boost Observations in Africa, is an initiative sponsored by the European Union under the Horizon Europe program that provides services in the areas of flood early warning and hydropower dam reservoir management.

Currently, only 40% of Africa's population has access to early warning systems for weather, climate, and water extremes, as reported by the World Meteorological Organization (WMO) Performance Monitoring System. There is a need for timely information on floods in order to take proactive measures to protect citizens and their property.

The TEMBO Africa Flood Early Warning Service (FEWS) is designed to enhance community safety by providing timely alerts about impending extreme weather events. By leveraging advanced forecasting technologies and data analysis, the TEMBO FEWS offers crucial warnings to residents in flood-prone regions, enabling them to take proactive measures to protect themselves and their property. The service integrates hydro-meteorological data, hydrological and hydraulic modelling, and meteorological forcing to predict potential flooding scenarios with high accuracy. With its user-friendly alerts and actionable insights, FEWS helps communities prepare for and mitigate the impact of severe weather, ultimately safeguarding lives and reducing property damage. Figure 2 gives an example of how communication with citizens takes place in Narok, Kenya, where the service is successfully piloted in collaboration with the Kenya Meteorological Service.

The main users of the service are national meteorological and disaster management agencies, government organizations, the financial sector, donors / NGOs and citizens. TEMBO Africa focuses on smaller cities with populations under 700,000, where there is a significant need for affordable flood warning systems.

More than 2000 dams have been constructed in sub-Saharan Africa, with over 200 more under development to improve food security and hydropower output. However, expected changes in climate, population, and agricultural patterns will test the ability of current and proposed dams to deliver the benefits that prompted their construction. As hydropower is required for most of the electricity production in Africa, it is necessary to equip hydropower plants with technologies that will allow them both perform better and reduce costs by preventing damage.

The main users of the service are the organizations responsible for dam reservoir management. These can be government agencies, para-statal organizations or private organizations responsible for dam reservoir management. They need near real-time information for water level, storage, wall/slope stability, bathymetry, inflows, hydrological forecast, sedimentation, actual rainfall and rainfall forecast, evaporation, land use changes, and energy generation, to enable them to make informed decisions for reservoir management.

TEMBO Africa has developed a service that provides this information and has carried out pilots for the Bui Power Authority in Ghana and the Lunsemfwa HydroPower Company in Zambia. This has yielded valuable and positive feedback, highlighting the service's practical value. Each dam has its own particular challenges, from software legacies to specific physical settings. By organizing co-creation sessions with individual power companies, TEMBO Africa is able to rapidly ascertain what is needed.

The methodologies used for the flood early warning service and the hydropower dam reservoir management services are similar. A hydrological model is developed, with TEMBO Africa floodplain mapping and bathymetry (for reservoirs) as input. This combined with rainfall information from local weather stations (such as those of TEMBO Africa partner TAHMO), soil moisture maps, and river discharge maps leads to the generation of large scale flood forecast maps.

TEMBO Africa makes use of a combination of satellite and in situ Earth observation data. In addition, satellite communications are used to transfer data, which is very important to make the solutions cost-effective. Satellite data are used that are openly and freely available, in particular Sentinel-1 data for water levels and soil moisture and other satellite data for digital elevation models. GNSS signals are used for determining water levels, water vapor and soil moisture, although this is still in an experimental stage. GNSS is also used for measuring dam displacement and RTK GPS for bathymetry.

TEMBO Africa uses a variety of technical resources to provide drastic cost cuts to water monitoring solutions. By introducing robust hardware with easily replaceable parts, the project has delivered inexpensive monitoring equipment. New sensors and innovative ways to use existing sensors are used to deliver affordable results in the African context.

The first example is river discharge measurement. TEMBO Africa offers real-time water level and discharge data in rivers and canals, using a camera taking videos at regular intervals. For rivers up to 50 meters, a small camera system, the “PtBox” is available and can be paired with different kinds of software. For wider rivers, a larger system is used, the DischargeKeeper.

The low-cost global navigation satellite system (GNSS) sensors were already mentioned. These are versatile tools for near-real time monitoring. They measure ground and structural movements with sub-millimeter precision, water levels and soil moisture by analyzing satellite signal reflections, and support weather forecasting by capturing atmospheric water vapor. There is no contact with the water or the soil surface that is measured, which makes the solution especially robust. Data is sent to the cloud to be processed.

The TEMBO bathymetry service provides a precise underwater map of the shape and depth of reservoirs. The use of low-cost but high-accuracy sensors (fish finder and RTK), which provides centimeter-level positioning accuracy, enables a local company to perform low-cost, high-quality surveys without specialized expertise. The service delivers the true storage capacity of a reservoir, identifies sediment buildup and provides data to support dredging decisions. This leads to better long-term reservoir management. This method has been tested in African reservoirs and offers a ten times or more cost reduction compared to traditional echo-sounder surveys.

The TEMBO Africa services aim at achieving the following impacts.

A goal of TEMBO Africa is making sure that solutions are marketable and sustainable. Establishing local enterprises that maintain water monitoring infrastructure is key, e.g. working with TAHMO weather stations, TEMBO Africa ensures its solutions are embedded in an infrastructure well suited to the demands of the African environment. To contribute to open and free hydrometeorological data for Africa, TEMBO Africa is a pilot activity in the post-2025 work program of the Group on Earth Observations (GEO).