SIMULATING STREAMFLOW IN RESPONSE TO CLIMATE CHANGE IN THE UPPER EWASO NGIRO CATCHMENT, KENYA
Omwoyo M. Anne*, Nzioka John Muthama**, Alfred Opere*and Richard Onwonga**
*Department of Meteorology, University of Nairobi
**Wangari Maathai Institute for Peace and Environmental Studies
***Department of Land Resource Management and Agricultural Technology, University of Nairobi
Address: P.O Box 30197 - 00100, Nairobi.
(Received 19 October 2016, Received in revised form 10 November 2016, Accepted 26 January 2017)
The study simulated streamflow response under changing climate for Ewaso Ngiro river in Upper Ewaso Ngiro Catchment (UENC), using Soil and Water Assessment Tool (SWAT). Data from National Centre for Meteorological research (CNRM) model of Co-Ordinated Regional Downscaling Experiment (CORDEX) was used to generate climate change scenarios (temperature and rainfall) for representative concentration pathway (RCP) 4.5 and 8.5 from 2021-2080 relative to the baseline 1976-2005. SWAT model was set up using historical daily rainfall and temperature data, soils, Digital Elevation Model and land cover map, and calibrated against observed streamflow. Decreasing trend in historical rainfall and streamflow was observed while increasing trend was observed for temperature. Projections indicated increasing trend in temperature in both RCPs, with RCP 8.5 having higher increase (1.1-2.60 C) than RCP 4.5 (1.0-1.70 C). Rainfall was found to increase from March-November, and decreased in December-February in all scenarios. Change in total annual rainfall ranged from 0.1-18.5% in 2021-2050 and 1.2-18.7% in 2051-2080, which corresponded to increase in streamflow of 20.9-23.6% and 21.2-28.2% respectively. Streamflow in March-May decreased (-26 to -10%) in all scenarios and increased in June-February (9-114%). This was found contrary to streamflow patterns simulated in neighboring catchments where studies indicate increasing streamflow trend in March-May. Streamflow response was found to be sensitive to changes in rainfall, thus emphasis should be put on water conservation and catchment management including protection of headwater forests through agroforestry, afforestation and reforestation.
Key words: Climate change, Streamflow, Simulation, Upper Ewaso Ngiro Catchment