The design of strategic investments in water, energy and food (WEF) infrastructures is challenging because the size, location, technology mix and pace of development is made uncertain by multiple factors. For example, the return on investment, which comes long after building a hydropower dam, is made uncertain by local, regional and global climate and socio-economic factors. This is exacerbated by the challenges associated with the impacts of climate change, especially in sub-Saharan Africa (SSA) where it is difficult to model these impacts, hence leading to high levels of uncertainty in future scenarios (2050 and beyond).

Long-term investment planning and system operations for energy, depend on and compete with other sectors for, the availability of water (for hydropower and cooling thermal plants) and land resources (e.g. for biofuel production and arability). The efficient exploitation of land, energy and water resources and their synergised use for economic development therefore require an multidimensional integrated optimisation approach co-created with stakeholders in dialogue. This starts with planning followed by prioritised investments based on local, national and regional needs in the energy, agricultural and water sectors. This is mostly lacking in SSA at the moment. We gathered a selected group of experts in Accra, Ghana in November 2022 with a broad mix of experiences and expertise in the energy, water and agricultural sectors, who shared deeper insights and values of the need for integrated WEF planning to begin tackling challenges and opportunities identified in the Volta Basin in West Africa (starting with Ghana) and the Tana basin in Kenya. The main challenge identified was the disjointed planning of WEF infrastructures due to different financing mechanisms and siloed sectoral thinking; and participants raised emerging opportunities for planning infrastructure through transnational and regional cooperation as well as the need to build on existing and new initiatives devoid of entrenched political goals.

In this contribution, we will present some of the main findings from the meeting in Accra and share knowledge on how transparent WEF modelling can be contextualised for local operational relevance, and through co-creation, how interactive engagement tools can be used for planning, policy- and decision-making.@en

Plastic pollution in rivers threatens ecosystems, increases flood risk due to its accumulations at hydraulic structures and its final emissions into the ocean threaten aquatic life, especially and probably most in coastal urbanized areas. Previous work suggests that plastic pollution in these urban rivers is influenced by hydrometeorological and anthropogenic factors. However, the transport dynamics of the plastics in such rivers are non-linear and complex and remain largely unresolved. Here, we show that tidal dynamics can be the main driver of plastic transport closest to the river mouth. Outside the tidal zone, rainfall and river discharge were identified to be more important drivers. We monitored plastic transport in the Odaw river, Ghana during the dry season. The Odaw drains the densely populated city of Accra and discharges into the Gulf of Guinea. Data were collected between March and May 2021 (dry season), using visual counting at four bridges along the river, of which two were located within the tidal zone. We explored the correlations between river plastic transport, and rainfall, tidal dynamics, and river discharge. Finally, we estimated the total plastic mass transport by using item-to-mass conversion data from previously published literature. We observed a peak in plastic transport at the upstream bridge within the tidal zone after an increase in rainfall (7.3 times larger). We found a gradient of the hydrometeorological factors driving plastic transport. Closer to the river mouth, tidal dynamics were more strongly correlated with plastic transport than upstream. The daily mass transport was estimated to be between 1.4–3.8 × 10² kg/d, which is lower than previous model estimates. These results add to the evidence of inconsistent correlations between plastic transport and hydrometeorological variables. Long-term monitoring data is required to further investigate this. The results also support the hypothesis that tidal dynamics are a crucial factor in controlling the emissions of plastics from rivers into the ocean. The findings provide a baseline for the Odaw river during the dry season and allow for comparison with the wet season. The approach adopted here also serves as a blueprint for similar urban river systems, regionally and globally.

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The importance of small reservoirs for the livelihoods of people in the Upper East Region of Ghana cannot be over-emphasized. They are used for many purposes which include fishing, livestock watering, construction, irrigation, recreation, drinking water, and other domestic uses. The reservoirs were built most often close to communities to support them with dry season water use since the region has a mono-modal rainfall pattern (April – October). The best time to realise the full extent or capacity of small reservoirs is therefore at the beginning of November. This study was carried out in the Volta basin focusing on the Upper East Region as part of a larger Challenge Program for Water and Food and the EU H2020 TWIGA project. The shallowest (with a maximum depth less than 2m) reservoirs in the northern part of the Volta basin are often dry at the start of the Harmattan season (December - February) when they are most needed. The perception was that this was mainly a result of high rates of evaporation because of high temperatures (going up to 41oC) in that part of the basin in the dry season (Nov – April). Unfortunately, most of the reservoirs are ungauged making their management challenging. Remote Sensing methods have been used to monitor the reservoirs but mainly with regards to their distribution and capacities (surface areas). In this research, we studied the filling and emptying of the reservoirs with a combination of remote sensing and in situ data, offering better insights into the components of the water balance and energy budget for small reservoirs and thereby the possibility to manage them better. Aside the usage of water in reservoirs, evaporation is considered to be the main component of the water balance of a reservoir. Accurate estimation of evaporation is required for irrigation management and water resources planning. Knowledge of hydrologic fluxes, including evaporation, is required for monitoring, and understanding hydrological and ecological processes. It is however expensive to directly measure evaporation energy fluxes in the field continuously for a long period of time using the Eddy Covariance method. Following this study, a cost effective and reliable way of measuring evaporation flux is proposed using a TAHMO-like meteorological station and the FAO-56 Penman-Monteith method in CropWat. The main findings from the research are as follows: • Water abstraction for irrigation, including through small reservoirs of up to 10m3/s from the Volta river, will have minimal impact on hydropower generation at Akosombo and Kpong. However, increasing irrigation and small reservoir abstraction (or storage) rates to about 38m3/s would mean that the water demand for hydropower for some years will not be fully met (about 0.1 percent shortage may be experienced). This means the one-village-one dam project might not create many problems for hydropower generation downstream if they are well-managed (gains not offset by high water losses). • Evaporation from small reservoirs is not as high as expected. Average actual rate of evaporation is about 5mm/day instead of the reference evaporation of about 10mm/day estimated using meteorological variables from distant (> 3km) weather and climate stations. • Even though evaporation in small reservoirs is low, the rate of evaporation is higher in shallow and smaller reservoirs. The management of the small reservoirs will therefore require better landuse planning and water allocation to make them fit for the purpose for which they have been constructed for use in the dry season. • A combination of hydro-meteorological data from TAHMO-like stations and remote sensing offer a better way to monitor and manage the water use in small reservoirs. • Small reservoirs are good for community water management and not as inefficient as often thought. @en

In 2009, the International Soil Moisture Network (ISMN) was initiated as a community effort, funded by the European Space Agency, to serve as a centralised data hosting facility for globally available in situ soil moisture measurements . The ISMN brings together in situ soil moisture measurements collected and freely shared by a multitude of organisations, harmonises them in terms of units and sampling rates, applies advanced quality control, and stores them in a database. Users can freely retrieve the data from this database through an online web portal (https://ismn.earth/en/, last access: 28 October 2021). Meanwhile, the ISMN has evolved into the primary in situ soil moisture reference database worldwide, as evidenced by more than 3000 active users and over 1000 scientific publications referencing the data sets provided by the network. As of July 2021, the ISMN now contains the data of 71 networks and 2842 stations located all over the globe, with a time period spanning from 1952 to the present. The number of networks and stations covered by the ISMN is still growing, and approximately 70 % of the data sets contained in the database continue to be updated on a regular or irregular basis. The main scope of this paper is to inform readers about the evolution of the ISMN over the past decade, including a description of network and data set updates and quality control procedures. A comprehensive review of the existing literature making use of ISMN data is also provided in order to identify current limitations in functionality and data usage and to shape priorities for the next decade of operations of this unique community-based data repository.

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TAHMO In 2014, the Trans-African Hydro-Meteorological Observatory (TAHMO) was officially founded as a Dutch not-for-profit foundation. Now, five years later, TAHMO has become the largest provider of scientific weather and climate data for sub-Sahara Africa. The present network of 500 stations in 20 countries still falls well short of the final network of 20,000 stations but we should already consider TAHMO as a major success, as it has shown that it is possible to run a cost-effective observation network. TAHMO distinguishes itself through different approaches with respect to technology, operation, and financial sustainability. Innovations in all these aspects are needed to move forward and will be discussed in some detail during the presentation. Technology TAHMO has partnered with METER Group in the co-design of the current weather station. Originally, the thought was to develop a very cheap ($200) station ourselves but the engineering needed to move from a proof-of-concept to a fool-proof concept is more complex than one may think. Many ideas have been bounced between the two teams and tested in the field in Africa, leading to a third generation apparatus that is very robust. Operation Over 90% of TAHMO stations are placed at (secondary) schools. This provides some physical but especially social protection. Educational material is provided to engage teachers and students and to encourage them to help out with simple maintenance, such as cleaning. Also the IT backbone, developed with support through IBM's Corporate Social Responsibility activities is worth mentioning as it supports state-of-the-art QA/QC. Financial sustainability So far, most stations have been funded through projects funded by different donors and agencies. A large investment by IBM / Weather Underground formed the basis for a rapid expansion of 333 stations. To ensure long-term financial sustainability, TAHMO provides data services to commercial users. Clearly, value chains run from raw data to actionable information. Willingness to pay increases exponentially along that chain. For this reason TAHMO has become part of a network of entities that bridge the gap between weather station and information market.@en

A 3-D numerical method is developed to investigate the spatial distribution of surface fluxes over heterogeneous surfaces in (semi-)arid regions. Quantifying the effects of changes in the momentum, thermal and moisture roughness lengths on the airflow and fluxes in the ABL is important for water resources management and local climate studies. The governing equations and turbulence models are modified to include the effects of atmospheric stability conditions on the airflow. The turbulent airflow in ABL is simulated based on the Unsteady Reynolds-Averaged Navier-Stokes (URANS) approach to understand the air flow over the non-homogeneous surfaces from dry land through the water surface and vice versa. The model can be used to study airflow in neutral and non-neutral ABL over complex and non-homogeneous surfaces. The model results were used to investigate the flow parameters and (heat) flux variations over small water surfaces considering its surrounding conditions.@en

There is a lack of weather and climate observation stations in Africa, while food production, harvest predictions, and disaster mitigation would benefit from improved data-accessible observation. A new smart and sustainable weather and climate observation network now addresses the important challenge of monitoring the weather in the continent.@en

Earlier this year, the European Commission started funding the project “Transforming Water, weather, and climate information through In situ observations for Geo-services in Africa”, or TWIGA. ‘Twiga’ is the Swahili word for giraffe, an animal that derives a competitive advantage from carefully observing its environment. The project aims to develop new geo-services for the water and climate sectors through development of new sensors and associated value chains. Sensors at different Technology Readiness Levels are foreseen to be developed, tested, and embedded in actionable information services. Special emphasis is paid to ground-based sensors that enhance satellite observations. The consortium has eighteen partners from Europe and Africa, including SMEs, universities, and government organizations. Using the network of meteorological stations built in the framework of the TAHMO (Trans-African Hydro- Meteorological Observatory, see www.tahmo.org), new sensors can be rapidly deployed and tested at hundreds of sites in Africa. The present list of experimental sensors to be built and tested include: - 100 Euro neutron counter - Laser micro scintillometer - Evaporometer (developed at Oregon State University) - Intervalometer rain gauge* - Lightning tracking* - GNSS water vapor* - GNSS soil moisture status* The starred (*) sensors are sensors for which some early activities have been undertaken and for which results will be presented. For all sensors, the general idea and usefulness will be explained. Finally, TWIGA is an open project and we would like to extend an invitation to other research groups to use our network to test new sensors in our African network. This project is sponsored by the European Union through Project #776691 “TWIGA”. @en

Atmospheric stability conditions over the water surface can affect the evaporative and convective heat fluxes from the water surface. Atmospheric instability occurred 72.5% of the time and resulted in 44.7 and 89.2% increases in the average and maximum estimated evaporation, respectively, when compared to the neutral condition for a small shallow lake (Binaba) in Ghana. The proposed approach is based on the bulk-aerodynamic transfer method and the Monin-Obukhov similarity theory (MOST) using standard meteorological parameters measured over the surrounding land. For water surface temperature, a crucial parameter in heat flux estimation from water surfaces, an applicable method is proposed. This method was used to compute heat fluxes and compare them with observed heat fluxes. The heat flux model was validated using sensible heat fluxes measured with a 3-D sonic anemometer. The results show that an unstable atmospheric condition has a significant effect in enhancing evaporation alongside the sensible heat flux from water surfaces.@en

In this study, a framework for simulating the flow field and heat transfer processes in small shallow inland water bodies has been developed. As the dynamics and thermal structure of these water bodies are crucial in studying the quality of stored water , and in assessing the heat fluxes from their surfaces as well, the heat transfer and temperature simulations were modeled. The proposed model is able to simulate the full 3-D water flow and heat transfer in the water body by applying complex and time varying boundary conditions. In this model, the continuity, momentum and temperature equations together with the turbulence equations, which comprise the buoyancy effect, have been solved. This model is built on the Reynolds Averaged Navier Stokes (RANS) equations with the widely used Boussinesq approach to solve the turbulence issues of the flow field. Micrometeorological data were obtained from an Automatic Weather Station (AWS) installed on the site and combined with field bathymetric measurements for the model. In the framework developed, a simple, applicable and generalizable approach is proposed for preparing the geometry of small shallow water bodies using coarsely measured bathymetry. All parts of the framework are based on open-source tools, which is essential for developing countries.@en

Understanding of hydroclimatic processes in Africa has been hindered by the lack of in situ precipitation measurements. Satellite-based observations, in particular, the TRMM Multisatellite Precipitation Analysis (TMPA) have been pivotal to filling this void. The recently released Integrated Multisatellite Retrievals for GPM (IMERG) project aims to continue the legacy of its predecessor, TMPA, and provide higher-resolution data. Here, IMERG-V04A precipitation data are validated using in situ observations from the Trans-African Hydro-Meteorological Observatory (TAHMO) project. Various evaluation measures are examined over a select number of stations in West and East Africa. In addition, continent-wide comparisons are made between IMERG and TMPA. The results show that the performance of the satellite-based products varies by season, region, and the evaluation statistics. The precipitation diurnal cycle is relatively better captured by IMERG than TMPA. Both products exhibit a better agreement with gauge data in East Africa and humid West Africa than in the southern Sahel. However, a clear advantage for IMERG is not apparent in detecting the annual cycle. Although all gridded products used here reasonably capture the annual cycle, some differences are evident during the short rains in East Africa. Direct comparison between IMERG and TMPA over the entire continent reveals that the similarity between the two products is also regionally heterogeneous. Except for Zimbabwe and Madagascar, where both satellite-based observations present a good agreement, the two products generally have their largest differences over mountainous regions. IMERG seems to have achieved a reduction in the positive bias evident in TMPA over Lake Victoria.

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The Trans-African Hydro-Meteorological Observatory (TAHMO) is an initiative that seeks to make Africa an extremely well monitored continent. Ideally, there would be one station every thirty kilometers, or 20,000 in total. The stations we use are robust and have no moving parts, thereby greatly reducing the burden of maintenance. The costs are relatively moderate given the high performance, meeting the WMO standards. Most stations are placed at schools where they are integrated in the curriculum, while receiving physical and social protection. Perhaps most challenging is the fact that we try to cover the costs through selling data for commercial purposes. During the past year, TAHMO network development has accelerated tremendously. In this presentation, we describe the various pathways along which this has taken place. The transition from a "nice idea", to a professional organization operating in fifteen countries is interesting and far from trivial. We have encountered various pitfalls along the way but also have learned a lot about operating the network. Finally, the different innovations in sensors and an outlook to further development will be given. @en

An unsteady fully three-dimensional model of Lake Binaba (a shallow small reservoir) in semi-arid Upper East Region of Ghana has been developed to simulate its temperature dynamics. The model developed is built on the Reynolds Averaged Navier-Stokes (RANS) equations, utilizing the Boussinesq approach. As the results of the model are significantly affected by the physical conditions on the boundaries, allocating appropriate boundary conditions, particularly over a water surface, is essential in simulating the lake's thermal structure. The thermal effects of incoming short-wave radiation implemented as a heat source term in the temperature equation, while the heat fluxes at the free water surface, which depend on wind speed, air temperature, and atmospheric stability conditions are considered as temperature boundary condition. The model equations were solved using OpenFOAM CFD toolbox. As the flow is completely turbulent, which is affected by the complex boundary conditions, a new heat transfer solver and turbulence model were developed to investigate the spatial and temporal distribution of temperature in small and shallow inland water bodies using improved time-dependent boundary conditions. The computed temperature values were compared with four days of observed field data. Simulated and observed temperature profiles show reasonable agreement where the root mean square error (RMSE) over the simulation period ranges from 0.11 to 0.44 °C in temporal temperature profiles with an average value of 0.33 °C. Results indicate that the model is able to simulate the flow variables and the temperature distribution in small inland water bodies with complex bathymetry.

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