Impacts of Climate and Land Use Changes on Vea Catchment and Irrigation Scheme in Upper East Region of Ghana

Abstract

Vea catchment hosts one of the two major irrigation schemes in the Upper East Region of Ghana, inhabited by many rural farming communities and offers opportunity for all-year-round agricultural production for these communities. The catchment will continue to experience irrigation expansion and upsurge in domestic water demands due to population growth and urbanisation. Any adverse effects of climate change (CC) will be an add-on pressure on the catchment water resources and will be detrimental to the entire population in the area. This study assessed the influence of CC on future water resources availability in the catchment for irrigation and also examined land use/cover changes in the area. Water mass balance method was used to estimate historical streamflow for the catchment with the bathymetry data and the storage-area-height relationship (function) at the irrigation reservoir site. The IHACRES rainfall-runoff model was successfully calibrated and validated for future flow prediction using outputs from all the Regional Climate Models (RCMs) of Coordinated Regional Downscaling Experiment (CORDEX) that provided data for the Africa domain based on the highest emission scenario (RCP8.5). Based on socioeconomic scenarios drawn from survey data gathered through household and institutional interviews, focus group discussions and review of national policies on CC, the water allocation and planning model, WEAP, was successfully configured and used to assess future water availability situation in the catchment in two future periods, 2021-2050 and 2071-2100. Climatic data for the period 1972-2012 from four stations were additionally analysed. Landsat satellite imagery was also analysed to assess land use/cover changes in the catchment. The results indicate a rising trend in both historic and projected temperature and evapotranspiration over the past 41 years and in the next decades. No long-term trend and no variability changes in rainfall data were evident. With the lowest streamflow derived from RCMs simulated conditions and the current irrigation rate of 1.1%, the catchment will experience average annual water supply deficit (AWSD) of about 1.3 x 106 m3 and 1.8 x 106 m3 in the periods 2021-2050 and 2071-2100 respectively. If the potential irrigable area (1400 ha) of the catchment is developed under the current practices, both lowest and highest streamflow derived from RCMs simulated conditions indicate that in the period 2071-2100 the catchment will experience AWSD of about 3.3 x 106 m3 and 0.7 x 106 m3 respectively. Closed and open savanna woodland cover in the catchment decreased by about 55.7% and 44.2% respectively between 1990-2010 while grass/herbaceous cover and bare surface/built-up areas increased by about 168.5% and 203.0% respectively over the same period. The study indicates a projected v considerable shortfall in water availability for irrigation in the coming decades due to CC coupled with population growth and associated water demand. Government and stakeholder organisations need to assist farmers by providing alternative irrigation facilities with improved irrigation efficiency in order to sustain livelihoods of farmers on the long run. This should go along with the introduction of new improved seeds and drought resistant crops to farmers. Land cover restoration programmes that include incentives for protection of forest reserves be introduced to curtail the high pace depletion of the vegetation cover in the area.