Impacts of land-use and land-cover changes on flow regimes of the Usangu wetland and the Great Ruaha River, Tanzania

A study was conducted to investigate the hydrological impacts of land-use and land-cover changes on flow regimes of the Great Ruaha River. Remote sensing and GIS techniques were used to inventory temporal changes of land-use and land-cover changes in the watershed. Hydrological data were analyzed to reveal the alterations and trends for three time periods; pre-1974, 1974-1975, and post-1985. It was revealed that there was a steady increase in cultivated area, from 121.2 km2 to 874.3 km2 between 1973 and 2000 while the woodland area decreased significantly over years. The minimum dry season area of the wetland declined significantly, with major changes occurring between 1984 and 2000. River flows were found to be highly variable within and between the years, and sensitive to land-use and land-cover changes. There was a slight shift of the time peak flows, from April to early February during the post-1985 period. The Q50 flow progressively declined from 19.23 m3 s-1 in the pre-1974 to 16.51 m3 s-1 and 9.04 m3 s-1 for 1974-1975 and post-1985 period. The Q95 (low flow) declined from 2.84 m3 s-1 to 0.11 m3 s-1 and 0.0 m3 s-1 for pre-1974, 1974-1975 and post-1985 period. The study concludes that the modification of the land use and cover has resulted in changes in temporal distribution of runoff. The study highlights the importance of considering effects of land-use and land-cover changes on ecosystems and water resources for an informed decision on proper catchment planning and management. © 2008 Elsevier Ltd. All rights reserved.