Ghana depends on agriculture for about 60% of gross national product and it provides work for about 80% of the population. Meanwhile, agriculture is almost wholly on a rain-fed basis. With an increasing population and growing demand for food, the economy can no longer depend on rain-fed agriculture. For the past 20 years, Ghana has experienced drought periods and erratic rainfall. Irrigation is therefore the way forward in agriculture if the country is to solve the food security problem. This is especially so in northern Ghana and Burkina Faso, where the rainy season lasts for only 4 to 5 months. The formal irrigation projects in Ghana (about 22 of them), which are sometimes referred to as large-scale irrigation, are almost overwhelmed with problems of finance, operation, management, etc. and therefore their impact is not notable in the economy. Small-scale irrigation development in the inland valleys, where one does not need huge initial capital, seems to have good potential in the short term. Irrigation development therefore will be very important in the economies of the countries in the basin.

As indicators for the food production sector, the total tonnage produced is used for two important crops, rice and maize. Rice is taken as representative for irrigated crops and maize for rain-fed crops. The SWAT field model was used to simulate crop productions for these two crops under the A2 and B2 scenarios. The Hadley A2 scenario simulation showed an increase in average yield from 3249 kg/ha to 3903 kg/ha and to 4688 kg/ha in the future under climate change (Fig. 9.4). The trend is similar for Hadley B2.

Maize on the other hand did not show much increase in the medium term (2010-2039) and rather a decrease in the long term for the Hadley A2 scenario. In the case of Hadley B2 there was virtually no change in yield.

As an input into the basin modelling, the yields in the SWAP field-level predictions in kg/ha were converted into production values by multiplying by the area under cultivation (FAO, 2003) for rain-fed and irrigation conditions (Table 9.3).

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