Assessment of the impacts of landuse and climate variability onflooding: the case of Manafwa catchment, Eastern Uganda

Flooding and drought are a natural environmental events occurring in many countries in the world causing fatal economic and human losses. The occurrence of these events is increasing due to alteration of local hydrological cycle through climate change or variability and anthropogenic factors. Climate variability/change and land use change have varied impacts on the peak flows and river discharges. As a result, these have major influence on flooding of a basin. Manafwa River in Eastern Uganda floods regularly causing inundations to the downstream plains. This study aimed at assessing the impacts of land use/cover (LULC) change and climate variability to the recurrent flooding in the area using Soil and Water Assessment Tool (SWAT) and GIS techniques. LULC change analysis showed farmlands dominate by 89.2 %, wetlands 3.9 % and forest 4.6% of the total area of the catchment. A decrease of 0.8% in a forest cover, 3.9% in wetlands and an increase of 3.5% and 0.4% in the farmlands and buildup respectively have been noticed between 1980 -2016. Statistical analysis showed greatest climate variability in the driest season and increasing amounts of rainfall in the SON and DJF seasons. Mann-Kendall trend analysis revealed an insignificantly increasing trend of Mean Annual Rainfall (MAR), maximum annual peaks and a significantly increasing trend in the annual average mean temperature at 0.030C yr-1 at the level of significance, p< 0.01. The SWAT model results revealed an increase in the highest flow peak by 0.31% due conversion of forests and wetlands to farmlands and settlements, 0. 89% due to climate variability and 1.1% due to the combined effect of LULC and climate variability since 1980. These results can be used in establishing a proper land use management and climate policy for reduction of flooding in the catchment.