AN ASSESSMENT OF THE POTENTIAL IMPACTS OF CLIMATE CHANGE ON WATER RESOURCES AND AGRICULTURE ON THE LOFA RIVER BASIN USING GIS-BASED SWAT MODEL

Abstract

Climate change and other anthropogenic factors impact water resources globally, and expected to further intensify due to increasing temperature, changing rainfall patterns, population growth, increased industrialization, economic growth and increase in pollution. A GIS-based SWAT Model integrated with Remote Sensing data was applied estimate impacts of climate change on water resources including agriculture on the basin of Lofa River in Liberia. The Lofa is situated in Liberia’s North-Western region. It lies between 7°N to 8°N and -9°W 11°W, and it is the 6th largest river in Liberia with about 10,612 km2 . It has it origin in the Guinea high land and run through Lofa, Gbarpolu, Grand Cape Mount and Bomi counties and enters into the Atlantic Ocean. The river is the provides water for about 500,000 inhabitants for domestic, agriculture, industrial, and other purposes Under the study investigation were carried out investigate impacts of climate change and LULC changes on the basin’s hydrological processes. The model’s performance results were found satisfactorily good, indicating that simulated and observed streamflow data were in good agreement, where the Nash-Sutcliffe coefficients (ENS) were 0.87 and 0.90 and coefficient of determination (R2 ) as 0.97 and 0.97 for the calibration and validation, respectively. Temperature, precipitation and streamflow trend and magnitude of change analysis were performed using the Mann-Kendall trend test and Sens’s slope estimator. Climate change impacts were observed in temperature, rainfall, and streamflow in the study area from 1984 to 2020, where a 1.4◦C and 2.7◦C increased were recorded in annual mean and maxmum temperatures respectively. The analysis of annual precipitation indicated a decrease in annual average precipitation by about -28%, while annual maximum precipitation reduced by 9.6% from 1984 to 2020. On the other hand, annual minimum precipitation increased by 13.8%. Similarly, annual and seasonal streamflows were significantly decreased. The analysis indicated that wet season streamflow reduced by about 21%, while dry season streamflow reduced by 11.8%, respectively. LULC also significantly impacted hydrological processes in the basin, contributing to high shallow overflow and decrease ground water recharge. Streamflow as the result of LULC changes in 1984 was 556 m3/s but increased to 964m3/s in 2020 during wet seasons. Similarly, surface runoff for the year 1984 was 893 mm, but increased to 966.9mm in the year 2020, while groundwater reduced by about 35.7mm. Analysis of LULC indicated significant changes in LULC classes from 1984 to 2020. The agricultural area increased from 3.99% to 20.85%. Forest reduced from 49.95% to 23.04%, while shrub land increased from 43.2% to 49.9%. Residential areas increased from4.04% to 5.22%, while water bodies decreased from 1.5% to 1.04%, respectively.