| dc.description.abstract | The Upper River Yala, which is a very important tributary of Lake Victoria, has been subjected to a
lot of discharge variation owing to the high intensity rains and the growing climate variability.
Extreme weathers have changed the streamflow patterns, and there is a high association between
tributary inflows and precipitation. In spite of the forecasts of the inter-annual discharge variation, a
uniform trend was not yet determined about when the peak or the minimum flow occurs. Past
research has looked at rainfall runoff relations but has not estimated the combined effects that
climate variability and land use alterations have on discharge especially in the upper Yala catchment.
The primary aim of this research was to model the effects of climatic variability on the discharge in
the Upper River Yala Basin, Kenya. These objectives were to: simulate the effect of temperature
variability on discharge; simulate the effect of rainfall variability on discharge; and to determine the
effect of simulated climate variability on discharge in different land use and land cover cases. Based
on historical daily temperatures and precipitation records (19902019), the Soil and Water
Assessment Tool (SWAT) was installed to model the hydrological responses when different climatic
and land cover conditions occurred. River gauging station data was used to calibrate and validate the
model (19902006 and 20072019 respectively). It was found that discharge is highly dependent on the
temperature and variability of rainfall. Rises in temperature correlated with higher river flows
(coefficient = 11.264) and the effect of the maximum temperature was heavy compared to the effect
of the minimum temperature. Rainfall became the most dominant factor and it contributed to 94.2%
of the discharge variation (correlation coefficient = 0.963). High discharges were seen to occur with
high rainfalls and low discharges during dry seasons. Changes in land use especially agricultural
development and deforestation were noted to cause a reduction in river flow during the dry season
and increase in river flow during the wet season. Dry season discharge decreased at 2.1 m 3 /s and
1.68 m 3 /s and wet season discharge climbed at 1.18 m 3 /s and 5.69 m 3 /s which signifies less
water availability and more flows and risk of flood. These results indicate that climatic variability
and altered land use have amplified seasonal variations on river discharge, lessening dry season
flows and amplifying wet season flows. The temperature change had a major influence on the river
flow, and an increase in the temperatures led to a decrease in the dry season discharge and the
change in seasonal water supply. Times of change in discharge were also due to rainfall variability
where low rainfall caused a decrease in dry season flows and high rainfall events causing a rise in the
wet season flows indicating that the basin is sensitive to rainfall variability. Temperature and rainfall
fluctuation together with land use alterations like agricultural growth and deforestation aggravated
seasonal discharge distributions. This highlights the interactive action of climate and human
activities on the dynamics of the rivers. The literature finds that climate variability, especially,
rainfall and temperature changes, and land use processes have a significant influence on the pattern
of discharges in rivers. It suggests that hydrological models need to be incorporated with temperature
and rainfall variability, sustainable land use is needed, and the adoption of an Integrated Water
Resources Management (IWRM) framework should be used. Future research should incorporate
additional environmental variables, long-term climate scenarios, and ecological impacts, while
integrated climate–land use–hydrology models can improve prediction and support sustainable
management of the Upper Yala Basin. | en_US |
