Modelling the impacts of climate change on sediment yield in the Songwe River sub-Basin, Tanzania
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Date
2025-12-03
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Mbeya University of science of and Technology
Abstract
Environmental decline driven by climate change affects hydrological and sedimentation processes, eventually, resulting to variations in sediment transport. The changes in temperature and precipitation are evident in developing countries including Tanzania. The Songwe River sub-basin is one of the areas climate changes which has experienced an increase in sediment production. However, there limited modelling studies that assess the impacts of climate change on sediment yield in the Songwe River sub-basin. This study aimed to model the impacts of climate change on sediment yield in the Songwe River sub-basin. The Soil and Water Assessment Tool (SWAT) model and QGIS software were used to simulate sediment yield under historical climate conditions (1984–2005) and future climate projections (2011–2040, 2041–2070 and 2071–2100) for RCP4.5 and RCP8.5. Precipitation and temperature data were obtained from four selected CORDEX regional climate models (CCLM4, HIRHAM5, RACMO22T and RCA4) driven by different General Circulation Models (GCMs). Bias correction of regional climate models (RCMs) output was done by using linear scaling method. Land use and land cover (LULC) maps for 1990, 2000 and 2020 were created from Landsat TM and OLI_TIRS imagery with supervised classification using the Maximum Likelihood Algorithm and Kappa statistics for accuracy assessment. Future LULC changes for 2040, 2070 and 2100 were projected using the Cellular Automata (CA) – Markov Model. The bias-corrected RCM outputs and LULC maps for 2020, 2040, 2070 and 2100 were input into the calibrated SWAT model to simulate sediment yield with results compared across the RCMs. The Soil Conservation Service (SCS) Curve Number for Moisture Condition II (CN2) was identified as the most sensitive parameter for simulating sediment yield. The findings indicate an increase in sediment yield over time with the most significant rise under the RCP8.5 scenario particularly in the late century where sediment yield could increase by 35–50%. The models projected a 10–15% increase in sediment yield by 2040, rising to 20–35% by 2070 with HIRHAM5 showing the largest increase. The study emphasizes the importance of a multi-model approach and highlights the vulnerability of elevated sub-basins near agricultural areas to increased sedimentation. The findings support incorporating climate change adaptation strategies into national and regional water and land management policies.
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This Thesis was published by Mbeya University of Science and Technology in 2025