Impact of climate and land use land cover change on water quality in Sironko catchment, Mt. Elgon

Abstract

Surface water quality underpins a range of livelihood means in Sironko catchment. This study determined the impacts of climate and Land use Land Cover Change (LULCC) on water quality in Sironko catchment. Field assessment of selected water quality from January to December 2018 followed standard procedures. Land use land cover change maps of Sironko catchment in 1986, 2000, 2016 and 2040 were developed by supervised classification. Baseline 1980-2009 and future climate scenarios 2025-2040 were downscaled by delta method. Stream flow, Total Suspended Solids (TSS), Total Nitrogen (TN), and Total Phosphorus (TP) loads were simulated using the Soil and Water Assessment Tool (SWAT). Mean values of selected water quality parameters were compared with the Uganda National Bureau of Standards (UNBS) guideline for clean surface water quality. t-test was employed at p < 0.05 level to determine any significant difference in water quality. Trends and trend magnitudes were determined using the Mann– Kendall trend test and Sen’s slope estimator. The contribution of climate and LULCs on stream flow, TSS, TN, and TP were computed using a second powered matrix regression model. Results show that agricultural lands; forests; and wetlands areas reduced by 8 %; 32 %; and 20 %, respectively between 1986 and 2000. But between 2000 and 2016, forests and wetlands areas increased by 84 % and 5 % while woodlands and agricultural lands decreased by 43 % and 13% respectively. From 2016 to 2040, built-up areas are projected to increase by 74 %; agricultural lands by 5 %; and grasslands by 2 %; while wetlands will decrease by 9 % and woodlands by 7 %. Less variability was detected in March, April and May (MAM) rainfall 20 < CV 30. Annual rainfall will increase at p < 0.05 in Kumi and Nakapiripirit stations between 2025 and 2040 while mean temperature showed increasing trends at p < 0.05 between 1980 and 2009 and between 2025 and 2040. In terms of water quality parameters, Fecal coliforms were above UNBS limit of drinking water quality while significant seasonal differences were detected at p < 0.05 for pH, EC, TP, and DO. Whereas the impacts of both climate and LULCC on River flow are both significant at p < 0.05 levels between 2025 to 2040, climate change is projected to increase River flow more than LLCC while the latter is projected to increase TN more than climate change under both RCP 4.5 and RCP 8.5. Local communities should improve on their waste disposal mechanisms while they also adapt to and mitigate the impacts of climate and land use change on water quality in Sironko catchment