Assessment of the Impacts of Land-Use Change and Climate Change on Stream Discharge Using Soil and Water Assessment Tool (SWAT) Model

SWAT model was applied to predict the impacts of climate change and land use changes of two experimental watersheds in Southeastern Nigeria. The results showed that there was a 3.2% increase on the streamflow from 224.9107m³/s in 1985 to 232.0667m³/s in 2015 in Ajalli River Watershed due to the impact of the land use changes, whereas there was a slight 0.4% decrease of streamflow in Imo River Watershed from 8, 300.65m³/s in 1985 to 8, 271.98m³/s in 2015. The impact of the climate change was predicted between 2046 – 2064 and 2081 – 2099 against the historical baseline (1981 – 2000), using two climate change models (CCCMA and GFDL). The results showed that while the CCCMA models showed a decrease of 383.72m³/s and 2.1% in the streamflow of the Ajalli river watershed when projected between 2046 – 2064 as against the historical baseline, the GFDL model showed a corresponding decrease of 3358.58 m³/s and 18.9% in the streamflow of the Ajalli river watershed. However, when the climate change was projected to a future of 2081 – 2099, there was an increase of 1256.56 m³/s and 6.8% in the streamflow of the same watershed, but a decrease of 4540.70m³/s and 24.2% in the streamflow of Ajalli river watershed. For Imo river watershed, the CCCMA models showed a decrease of 1557.74 m³/s and 5.7% in the streamflow of Imo river watershed when projected between 2046 – 2064 as against the historical baseline, while the GFDL model showed a corresponding decrease of 377.55 m³/s and 1.4% in the streamflow of the Imo river watershed. However, when the climate change was projected to a future of 2081 – 2099, there was an increase of 1674.32 m³/s and 6.1% in the streamflow of the same watershed, but a decrease of 1244.96m³/s and 4.6% in the streamflow of Imo river watershed