Volta Dam, Ghana

Energy supply in Ghana - a long-range outlook

24 July 2014

Dr Vicky Pope, Met Office Head of Integration and Growth, describes her first trip to Ghana in February 2014 to attend a workshop on early warning systems organised by the United Nations Environment Programme.

Providing early warning of the seasonal average and extreme weather is a focus of practical activity by the United Nations as a response to climate change. Coincidentally, for many years we have been supplying products based on our seasonal forecast to the Volta River Authority in Ghana to support itshydroelectric power operations.

I frequently describe this use of our seasonal forecast as a good example of how cutting-edge science can be used for practical applications. Therefore, I was very keen to visit their operations centre when I learned that the workshop would be held at the Volta hotel just a few miles away. The hotel is in a lovely setting high on the hillside overlooking the main Volta Dam and is also owned by the Volta River Authority. The operations centre is in a set of fairly dilapidated buildings close to the second Volta Dam. However they proudly showed us the artist's impression of the new operation centre which is due to be built on the site soon.

The hour and a half that we spent with Emmanuel Osafo and his technical team, including our main contact Philip Pady, was one of the highlights of our trip. The Volta River authority is responsible for producing most of the electricity for Ghana, 60% of it is hydroelectric and 40% is thermal for which they need to use light crude oil. The oil is expensive and imported so they want to minimise its use and spread it across the season.

They use the seasonal forecast of Volta Lake levels to optimise the use of water and crude oil to minimise costs over the year. In all but one year the actual lake levels predicted at the beginning of the rainy season was within the range of possible levels that we had predicted. The predictions are updated each month and even in the single outlier the updated predictions were accurate.

Emmanuel and his team were enthusiastic about the quality of our seasonal forecasts and the value they provide in planning their water supply and usage. In contrast, they were very wary of daily forecasts of the weather. This is in stark contrast to the view of weather forecasting that we are familiar with in the UK.

What can be hard for non-meteorologists to understand is that this is not really a reflection on the quality of the science or the forecasts but rather a function of the predictability of the weather. In middle latitudes, where we live in the UK, the large-scale weather systems that approach us from the Atlantic and elsewhere take a few days to grow and develop and so they are captured very well in our forecasts, especially if we are only looking one day ahead. For timescales longer than a couple of weeks however, predicting when and how these weather systems will grow is very difficult, making long-term forecasts much more inaccurate. We cope with this unpredictability by running a series of forecasts to give the probability of a range of outcomes.

On the other hand, in the tropics, day-to-day rainfall comes in short, sometimes very localised but often very heavy bursts which can be difficult predict in detail. In many parts of the tropics, including Ghana, there are wet and dry seasons. In Ghana's case, the amount of rainfall falling over the rainy season is strongly influenced by what happens far away in the Pacific Ocean.

El Niño and la Niña have a strong influence across the tropics, and particularly in West Africa. These phenomena start with changes in the temperature of the Pacific Ocean and the effect gradually builds up in the atmosphere over a period of months and more widely across the globe. The seasonal forecast captures this process well once the changes in the ocean have started. Hence we are able to give useful information for planning the season's rainfall for a river catchment as large as the Volta. From this we can derive the impact on Volta Lake levels.

The trip to Ghana gave me the opportunity to witness the practical application of our forecasts. I was pleased that the scientific skill of our forecasts is being translated into benefits. We are enabling the best use of the natural resources of a developing country, ultimately helping the Volta River Authority to provide a more secure electricity supply for Ghana, while also being aware of water supply for other uses.

Dr Vicky Pope

Dr Vicky Pope, Met Office Head of Integration and Growth, started her career as a research scientist in the Met Office working on the ozone hole and later on climate change, running parts of the Met Office climate programme for around ten years.

Vicky's current role involves looking for new opportunities to make use of Met Office science to benefit governments and society. She has been working in the space, hydrology, transport and digital economy sectors to develop new services, as well as advisory roles on climate change.

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