Assessing the impact of anthropogenic activities and climate change on hydrology in Pra River Basin, Ghana

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This research investigated the climatic and land use and land cover changes on hydrology in the Pra River Basin, Ghana. Soil and water analysis tool model was adapted for the hydrological assessment. Double cumulative curve and visual image interpretation were used to select the satellite images for image classification. Markov- cellular automation model was used to predict future land use and land cover. Regional climate models data under representative concentration pathways 4.5 and 8.5 for the period 2022–2047, 2048-2073 and 2074-2099 were used for future climate change assessment. Weighting, scaling and ranking techniques were used to select models that best reproduce the observed data. Trend analysis of monthly, seasonal and annual rainfall showed significant reduction in the months of February and March at a rate of 73 mmyr−1 and 1.08 mmyr−1 respectively. Runoff analysis showed no significant change in the upstream part of Pra River Basin compared to the downstream showing significant upward trend with average rate of 465 m3 s−1 and 32.5 m3s−1 for the annual and dry season respectively. Anthropogenic activities and climate variability contributed 83 % and 17 % respectively to the changes in runoff between 1987 and 2010. Land use and land cover change analysis showed that cropland, settlement and mining areas increased respectively by 130.55 %, 198.45 % and 304.27 % between 1986 and 2016. Also, open forest, closed forest and water body declined respectively by 22.68 %, 41.50 % and 30.11 %. Changes in land use and land cover contributed to increase in surface runoff and water yield by 124.51 % and 40.13 % respectively. Baseflow and evapotranspiration reduced respectively by 30.08 % and 13.248 %. Impact of post- reclamation on hydrology showed that galamsey and small-scale backfilling contributed significantly to the increased annual surface runoffs and water yield, however, baseflow and percolation depicted significant reduction. The largescale mining showed no significant change in the hydrological components on reclaimed and natural background (unmined areas). Sediment yield from galamsey, small-scale and large-scale mining showed significant increase with reference to natural background. The representative concentration pathways 4.5 and 8.5 showed fluctuations in monthly and annual rainfall ranging between -14 % and 20 %. Climate change impact showed increase in streamflow throughout the study period. The study demonstrates the need to formulate sustainable strategies that will ensure conservation of the ecosystem.
A thesis submitted to the Department of Civil Engineering, Kwame Nkrumah University of Science and Technology, Kumasi in partial fulfillment of the requirements for the award degree of Doctor of Philosophy in Water Resources Engineering, May 2019
Anthropogenic, Climate change, hydrology, Pra river basin, Ghana, Markov- cellular automation model