Effects of Rapid Urbanization on the Hydrological Process of Nyabarongo River in Rwanda

The rapid growth of cities, fueled by population growth and economic development activities, has resulted in significant changes in land use within the Nyabarongo River basin. This study measured changes in hydrological parameters, such as river discharge, that can be attributed to urban expansion. The study uses a combination of remote sensing data, meteorological data, Geographic Information Systems (GIS) tools, an Excel database, and the HEC HMS simulation model to analyze historical land use patterns and correlate them with observed hydrological changes over the last five years. The key findings show that the Nyabarongo River basin has experienced significant land use and land cover (LULC) changes over the last five years, most notably a 6.79% annual decrease in rangeland, which has resulted in an annual increase of 9.1% in agricultural land and 12.73% in built area. This shift, fueled by urbanization, has converted significant rangeland into impervious surfaces, altering hydrological processes by increasing runoff coefficients. In addition, the HEC HMS simulation revealed an average annual peak discharge increase of 1.61%. The linear regression model revealed a correlation coefficient (r) of 0.84 between LULC changes and river discharge, implying that the conversion of natural land and forests in the Nyabarongo catchment into built-up areas (impervious surface) increases Nyaborongo river discharge. This study aimed to contribute to a broader understanding of the environmental impacts of urbanisation in developing countries and provide a baseline for policymakers to establish a framework to balance urban development with ecological preservation. Keywords:  Urbanization, Hydrological Process, Nyabarongo River, Rwanda