Assessing the Potential Impacts of Climate Change on Irrigation Water Use in Upper East Region of Ghana: A case study of Tono and Yea Irrigation Projects

Climate change is a global phenomenon associated with the emission of greenhouse gases into the atmosphere with the resultant effect of raising the global mean temperatures. Climate change will lead to an intensification of the global hydrological cycle and can have major impacts on regional water resources, affecting both ground and surface water supply for domestic and industrial uses, irrigation, hydropower generation, navigation, in-stream ecosystems and water-based recreation. The people in Upper East Region (UER) are mostly engaged in Agriculture which is mostly dependent on irrigation water provided by medium and small reservoirs. With increase in population and the need to meet food security under Ghana's poverty reduction strategy, more lands are envisaged to be put under irrigation. It is therefore imperative to look into the impacts of climate change on irrigation water use of the two medium reservoirs in the region, Tono and Vea irrigation projects. Historical water abstraction from Tono and Vea reservoirs were estimated. The irrigation needs of four major crops (rice, tomato, pepper and onion) grown during the dry season were computed using the CROP WAT model. Future climatic conditions for the year 2020, 2050 and 2080 were determined for the UER based on synthetic and general circulation models climate scenarios. Future irrigation needs were also computed based on future climatic conditions. Climate change adaptation measures were identified and reviewed by interviewing institutions who have a stake in climate change. Historical water abstraction from the Tono and Vea reservoirs for the cultivation of the four crops were far less than their maximum storage capacity. Historical water abstraction for the cultivation of the four crops for dry season farming ranged from 9.66 Mm3 to 27.67 Mm3 and 1.82 Mm3 to 8.88 Mm3 for Tono and Vea reservoirs respectively. The irrigation requirements of rice, tomato, pepper and onion based on climatic baseline (1977 - 2006) are 871.5 mm, 680.1 mm, 558.9 mm and 441.8 mm respectively. The net irrigation water requirements of the four crops will increase by about 0.6 - 9% due to climate change depending on the climate change scenarios and time slices. Climate change will not have significant impact on Tono irrigation project because future irrigation abstraction when maximum land areas between 1985 and 2006 are cultivated will be about 33 - 35 % of the maximum storage of the reservoir. Future irrigation abstraction when the total irrigable area at Tono is cultivated with rice, will be about 44% to 47% of the maximum storage capacity between 2020 and 2080 and therefore the total irrigable area of 2490 ha could be utilized for the cultivation of rice and other water demanding crops since there is abundance of water. Climate change will have a minimal impact on Vea reservoir but coupled with an increase in domestic abstraction, the stored water in the reservoir may not be adequate for both irrigation (when maximum land areas between 1985 and 2006 are cultivated in the future) and domestic use for 2050 and beyond. Furthermore, when the total irrigable area is cultivated, the stored water will be adequate for the cultivation of tomato, pepper and onion in 2020 with the exception of rice. The Vea reservoir could supply enough water for the cultivation of pepper and onion on the total irrigable area in 2050 because their irrigation abstractions are about 63% and 49% of the maximum storage capacity. In 2080, the Vea reservoir cannot supply enough water (over 51 % of total reservoir capacity) needed for the cultivation of each of the four crops on the total irrigable area because domestic abstraction will be about 52% of the maximum storage capacity. Climate change adaptation measures such as planting of crop varieties tolerant to adverse climatic conditions, efficient water management, and application of organic matter fortified with inorganic fertilizer if implemented can help farmers cope with climate change.

Source: KNUST