Assessing the effect of climate change on stream flow of River Kyambura

Abstract

River Kyambura relies on rainfall as one of its contributors to its stream flow therefore changes in the hydrological cycle due to climate change will have an effect on the streamflow and yet the magnitude of this effect was not known. This study focuses on the effects of climate change on the river. The rainfall and flow data obtained from the Ministry of water and Environment was first screened to make sure that the data is stationary and homogenous. This was done by carrying out Test for persistence and test for absence of trend. The changes in the climate in 2050 were obtained from MAGIC SCEGEN software for the two most likely scenarios; A1B and A2. A1B showed a 3% increase in the average annual rainfall and A2 showed a 6% increase in the average annual rainfall. HEC-HMS model was the hydrological model used to simulate the flow in River Kyambura. SCS –CN (Soil Conservation Curve Number) method was used in calculation of infiltration loses and transformation of excess precipitation to surface run off whereas Muskingum method was used to simulate the flow in the channel. The catchment was delineated in ArcGIS 10.1 using a 30m by 30m Digital elevation Model obtained from United States Geographic survey (USGS). The years 2006-2009 were used for calibration and 2010-2014 were used for validation. The HECHMS model was calibrated and validated to Nash-Sutcliffe of 0.62. The future flows in comparison with the current flows shows that flows shall be higher by 10% and 13%3 in the A1B and A2 scenario respectively. With this data, Ministry of Water and Environment can plan properly to prevent the effects that come with high flows.