Impacts of land cover and land use changes on stream flow: A case from the Nile Basin By Simon Mutie, Hussein Gadain, and Guleid Artan

Background Since 1960’s LULC changes have been a threat to life in the Nile Basin; High population increases has led to changes in land tenure systems resulting in deforestation expansion and intensification of agriculture; These changes in land cover have caused changes in the water balance of the basin.

Problem Statement Population growth rate 7.5%, High population = changes in land tenure systems, Deforestation and intensification of agriculture and overstocking, Reduction of perennial natural vegetation, Rise in bare and agricultural lands. Modifications of land cover and soils affect runoff hence water availability, High sedimentation and water quality concerns. Deforestation-Mau Wheat-Narok Flooding-Nzoia

Study Area Upper Nile Basin

Economic Importance of the basins Both basins originate from the indigenous and exotic greater Mau, Mt. Elgon and Cherangany forests. Large-scale/cash crop plantation –Tea, sugarcane, rice, wheat and high value horticultural crops. Small-scale mixed farming also practised Pastoralists with the nomadic Maasai community in Mara River basin. Mara basin houses the Serena-Mara-Serengeti wildlife sanctuary declared the seventh wonder in the world Swamps (Yala & Mosirori) which support a lot of biodiversity.

Major Ecosystem Threats Widespread encroachment and deforestation of the Mau forest tower, Mt Elgon Forest Rapid population growth and immigration into the basins. Expansion and intensification of agriculture Conversion and rehabilitation of basin wetlands for agricultural production e.g. Yala swamp Source: Nation media Deforestation-Mau Rice Growing-Yala swamp Overstocking-Mara Mosirori Swamp

Overall objective To determine the effects of land use & land cover changes on the river flow in the two basins

Source: USGS Pixel Resolution MSS – 79 * 56 m TM and ETM – 28.5 * 28.5 m Data and Methods LANDSAT images for the dry season (MSS and TM/ETM, for the years 1973, 1986 and the 2000 respectively) Image processing and classification; GPS used for surveys to collect ground-truth data on vegetation and land use/cover

False Color composite of bands 2,3&4 – 1986 data LULC Mapping

Land cover type 1973 (km 2 ) 1986 (km 2 ) 2000 (km 2 ) Change ( ) (km 2 ) Change (%) Forests Tea/Open forests Agricultural land Shrubland Grassland Savannah Wetlands Water Bodies LULC Changes Mara River Basin

Nzoia River Basin

No. Land Use Land Cover Type 1973 (km 2 ) 1986 (km 2 ) 2000 (km 2 ) Change ( ) (km 2 Change (%) 1Forests 2,8421, Shrubland 6, Agricultural Land 3,1529, Wetland Built up areas Water Bodies

Geo-spatial SFM System Diagram Preprocessing MAP MAE Basin Linkage Routing Parameters Soil Parameters Stream Flow Model Water Balance Lumped Routing Dist. Routing Streamflow Data Rain Evap Soil LU/LC DEM Obsv. S.Flow Data

Effects of Land use change on stream flow –Earlier than normal peaks –Higher peaks –Change in evaporation process –Soil erosion and sedimentation –produced streamflow at rainfall magnitudes that did not generate any streamflow with the 1973 dataset. –Changes are slight in Nzoia BasinItem MaraPeak flow (m 3 /s) m 3 /s Time to Peak (days) 158 th Julian day154 th Julian day Nzoia Peak flow (m 3 /s) m 3 /s Time to Peak (days) 126 th Julian day125 th Julian day

Conclusions There has been decline of natural vegetation in the two basins and a rise in land covers due to anthropogenic influences in the basin. The changes have caused higher and earlier occurrence of flood peaks. Increase in agriculture coupled with poor farming practices in the two basins has led to high sediment loads deposited on the river mouths. In Mara basin, sediment deposition at river mouth has caused backwater flow which has increased the wetland submerging farms. In Nzoia basin, deposition at lower river stages is raising the river channel, hence water topping the flood dykes every season

Potentialities/Limitations RS Limitations Data Availability Cost High cost analysing Potentialities Descision making and planning