Chapter 10
Hydrology and Climate Impacts
on Streamflow and Sediment Yield
in the Nyando River Basin, Kenya
J. U. Kitheka, S. Okoyo, and N. Mboya
Abstract This study seeks to establish the extent to which climate change and/or
variation is affecting streamflow variability and sediment transport in the Nyando
River Basin in Kenya. The basin is one of the country’s most important, because
it is a source of water for domestic use and irrigation. The river also discharges
water and sediment into Lake Victoria, one of the largest freshwater lakes in the
world. Data used in this study were obtained from the Water Resources Management
Authority (WARMA) and Kenya Meteorological Department (KMD), and include
river discharge, rainfall, and total suspended sediment for stations located in the
basin. Statistical methods and application of various hydrological data analyses of
time-series, flow duration, and Gumbel Distribution for flood flow analysis were used.
Land-use change was determined through analysis of Landsat satellite images and use
of overlay GIS techniques. Results show that there is significant variability in rainfall
and river discharge of the Nyando River, which can be attributed to climate variability.
There has also been major change in land use in the basin, which is evidenced by heavy
deforestation in the catchment areas for agriculture and settlement of the rapidly
increasing population. This increase in degraded areas, coupled with an increase in
runoff, has led to increased peak flood flows. The increase in frequency of flood
flows is attributed to rapid flow of surface runoff in degraded areas with low water
infiltration and percolation rates. However, the relationship between rainfall and river
discharge is strongly positive, reflecting the rapid hydrologic response to rainfall
input in the basin. There is also a strong positive relationship between sediment
discharge and river discharge. The increase or decrease of river discharge leads to
a corresponding change in sediment yield. As a result of land degradation and high
hydrologic response, the basin experiences high rates of soil erosion and sediment
yield. High hydrologic response also leads to flooding in the low-lying Kano plains.
Extreme streamflow variability in the plains has both direct and indirect impacts
that are ultimately increasing poverty levels in the basin. This study shows that the
effects of climate change and/or variability on the hydrologic systems in tropical
Africa are being compounded by population growth that has driven land-use change.
J. U. Kitheka (B) · S. Okoyo · N. Mboya
School of Environment, Water and Natural Resources, Department of Hydrology and Aquatic
Sciences, South Eastern Kenya University, Kitui County, Kenya
e-mail: jkitheka@seku.ac.ke; kolbio_kolbio@yahoo.com
© Springer Nature Switzerland AG 2021
S. Diop et al. (eds.), Climate Change and Water Resources in Africa,
https://doi.org/10.1007/978-3-030-61225-2_10
219
Hydrology and Climate Impacts
on Streamflow and Sediment Yield
in the Nyando River Basin, Kenya
J. U. Kitheka, S. Okoyo, and N. Mboya
Abstract This study seeks to establish the extent to which climate change and/or
variation is affecting streamflow variability and sediment transport in the Nyando
River Basin in Kenya. The basin is one of the country’s most important, because
it is a source of water for domestic use and irrigation. The river also discharges
water and sediment into Lake Victoria, one of the largest freshwater lakes in the
world. Data used in this study were obtained from the Water Resources Management
Authority (WARMA) and Kenya Meteorological Department (KMD), and include
river discharge, rainfall, and total suspended sediment for stations located in the
basin. Statistical methods and application of various hydrological data analyses of
time-series, flow duration, and Gumbel Distribution for flood flow analysis were used.
Land-use change was determined through analysis of Landsat satellite images and use
of overlay GIS techniques. Results show that there is significant variability in rainfall
and river discharge of the Nyando River, which can be attributed to climate variability.
There has also been major change in land use in the basin, which is evidenced by heavy
deforestation in the catchment areas for agriculture and settlement of the rapidly
increasing population. This increase in degraded areas, coupled with an increase in
runoff, has led to increased peak flood flows. The increase in frequency of flood
flows is attributed to rapid flow of surface runoff in degraded areas with low water
infiltration and percolation rates. However, the relationship between rainfall and river
discharge is strongly positive, reflecting the rapid hydrologic response to rainfall
input in the basin. There is also a strong positive relationship between sediment
discharge and river discharge. The increase or decrease of river discharge leads to
a corresponding change in sediment yield. As a result of land degradation and high
hydrologic response, the basin experiences high rates of soil erosion and sediment
yield. High hydrologic response also leads to flooding in the low-lying Kano plains.
Extreme streamflow variability in the plains has both direct and indirect impacts
that are ultimately increasing poverty levels in the basin. This study shows that the
effects of climate change and/or variability on the hydrologic systems in tropical
Africa are being compounded by population growth that has driven land-use change.
J. U. Kitheka (B) · S. Okoyo · N. Mboya
School of Environment, Water and Natural Resources, Department of Hydrology and Aquatic
Sciences, South Eastern Kenya University, Kitui County, Kenya
e-mail: jkitheka@seku.ac.ke; kolbio_kolbio@yahoo.com
© Springer Nature Switzerland AG 2021
S. Diop et al. (eds.), Climate Change and Water Resources in Africa,
https://doi.org/10.1007/978-3-030-61225-2_10
219