Impacts of climate variability and land use land cover change on stream flow in the little Ruaha river catchment, Tanzania

Abstract

A study was conducted to investigate the hydrological impacts of land use land-cover changes and climate variability on stream flow of the Little Ruaha River. Remote sensing and GIS techniques and Soil and Water Assessment Tool (SWAT) model were used. Landsat TM and ETM+ images of 1990, 1998 and 2011 were used to locate and quantify the changes which have occurred in the catchment. The reason to select these periods was to get good and clear images; there were no clear images for 1980.The study revealed a significant change in land use land cover within a period of 21 years. Between 1990and 1998, the woodland and wetland covers declined by 2.6% and 9% per year, and 1998 and 2011 declined by 1.4% and 3.1% per year, respectively .Physical based SWAT model was calibrated for the period 2000 to 2006 based on the available climatic data and was validated for the period 2007 to 2009. The Nash-Sutcliffe model efficiency (ENS) and coefficient of determination (R2) for annual flow were 58% and 65% respectively during calibration period and 72.68% and 77.35% during validation period respectively. Both land use land cover change and climate variability decreased runoff by 23% and 59.67% respectively. The climate variability influenced the surface hydrology more significantly than land use land cover change in Little Ruaha River catchment. The study concludes that, the modification of the land use and land cover and climate variability has resulted in changes in temporal distribution of runoff. The study highlights the importance of considering effects of land use land cover changes and climate variability on ecosystems and water resources for an informed decision on proper catchment planning and management.