10 Hydrology and Climate Impacts on Streamflow and Sediment …
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major socio-economic impacts on communities. However, these are generally undervalued by both national and international disaster management and development
policies and represent a challenge for disaster risk reduction (Mutua 2001).
The problem of sediment production and transport subject to climate change
within the basin must be examined, because it has major socio-economic implications
for communities and the country. Past studies have shown that land degradation
occurring on fragile slopes in the Nyando River Basin is responsible for high rates
of soil erosion (ICRAF 2000), which leads to high sediment load, and is thought to
be influenced by factors such as land use, vegetation cover, runoff dynamics, and
rainfall variability. There is, however, limited data and information on the extent
to which extreme hydrologic events and land-use change have altered the sediment
load delivered to Lake Victoria by the Nyando River. Because of this, assessment of
the influence of rainfall, river discharge, and land-use change is important because
these factors are highly variable as a result of climate and land-use change, with
big implications for the Nyando River Basin. The object of this study is therefore to
establish the extent to which climate change is affecting streamflow variability and
sediment transport in the Nyando River Basin in Kenya, an important aspect of the
current debate on the impacts of climate on water resources in Africa.
2 Description of the Study Area
2.1 Location
The Nyando River Basin is located in the Western region of Kenya between longitudes
0
o 50’S and 0
o 10’S and between latitudes 33
o 05’E and 34
o 25’E (Fig. 1). The river
originates from the Nandi Hills and Nyabondo Escarpment and drains into the Winam
Gulf in Lake Victoria (LBDA 1992; Republic of Kenya 2001a). It has a total length
of 170 km and a surface area of 3,517 km
2 . The main source of the rivers is in the
forested highlands at an altitude of 3,000 m above sea level (Kamau 2016).
2.2 Climate
The Nyando River Basin experiences two rainfall seasons. The long rainy season
is between March–April–May (MAM), and the short rainy season is between
September–October–November (SON). The average annual total rainfall ranges from
about 1100–1600 mm. The highland areas of the basin experience higher amounts
of rainfall (1800 mm) compared to the middle and lower areas that receive between
600 and 1100 mm of rainfall annually (ICRAF 2000 and 2002). The mean minimum
annual temperatures ranging from 14 °C to 18 °C are recorded from June to July. The
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major socio-economic impacts on communities. However, these are generally undervalued by both national and international disaster management and development
policies and represent a challenge for disaster risk reduction (Mutua 2001).
The problem of sediment production and transport subject to climate change
within the basin must be examined, because it has major socio-economic implications
for communities and the country. Past studies have shown that land degradation
occurring on fragile slopes in the Nyando River Basin is responsible for high rates
of soil erosion (ICRAF 2000), which leads to high sediment load, and is thought to
be influenced by factors such as land use, vegetation cover, runoff dynamics, and
rainfall variability. There is, however, limited data and information on the extent
to which extreme hydrologic events and land-use change have altered the sediment
load delivered to Lake Victoria by the Nyando River. Because of this, assessment of
the influence of rainfall, river discharge, and land-use change is important because
these factors are highly variable as a result of climate and land-use change, with
big implications for the Nyando River Basin. The object of this study is therefore to
establish the extent to which climate change is affecting streamflow variability and
sediment transport in the Nyando River Basin in Kenya, an important aspect of the
current debate on the impacts of climate on water resources in Africa.
2 Description of the Study Area
2.1 Location
The Nyando River Basin is located in the Western region of Kenya between longitudes
0
o 50’S and 0
o 10’S and between latitudes 33
o 05’E and 34
o 25’E (Fig. 1). The river
originates from the Nandi Hills and Nyabondo Escarpment and drains into the Winam
Gulf in Lake Victoria (LBDA 1992; Republic of Kenya 2001a). It has a total length
of 170 km and a surface area of 3,517 km
2 . The main source of the rivers is in the
forested highlands at an altitude of 3,000 m above sea level (Kamau 2016).
2.2 Climate
The Nyando River Basin experiences two rainfall seasons. The long rainy season
is between March–April–May (MAM), and the short rainy season is between
September–October–November (SON). The average annual total rainfall ranges from
about 1100–1600 mm. The highland areas of the basin experience higher amounts
of rainfall (1800 mm) compared to the middle and lower areas that receive between
600 and 1100 mm of rainfall annually (ICRAF 2000 and 2002). The mean minimum
annual temperatures ranging from 14 °C to 18 °C are recorded from June to July. The