Mr. Rwigi's Bio

Dr. Stephen Rwigi, a holder of PhD in meteorology, University of Nairobi, is a lecturer in the Department of Earth and Climate Sciences, University of Nairobi specializing in Hydrometeorology and Climate Change. His research interests are in the field of surface water resources with a view to inform policy in water resources management under a changing climate.

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Rwigi, S, Ouma G, Ouma C, Oloo F, Wekesa S, Olang L.  2021.  Effects of rainfall variability on water availability in the drylands of Northern Kenya under a changing climate, December 2021. AGU Fall Meeting Abstracts. Abstract

The availability of water in the dryland regions is a function of climatic and land conditions, which determine the amount and distribution of atmospheric water and subsequent partitioning of that water into different hydrological components. Rainfall variability in the drylands affects water, food and livelihood security in the sensitive landscapes. For effective water resource management, it is important to quantify the effect of rainfall variability on the available water resource components to support food security, given that a majority of livelihoods in the drylands are dependent on rainfall. This study assessed rainfall variability and its effects on stream flows in the dryland regions of Turkana County in Northern Kenya. The Coefficient of Variation (CV), Standardised Precipitation Anomaly (SPA) and Mann-Kendal test approaches were used to determine variability and trends of rainfall. The Soil and Water Assessment Tool (SWAT), was employed to simulate hydrological components, including surface runoff, interflow, groundwater flow and the eventual water yield in the streams. The model simulations were driven by the Climate Hazards Group InfraRed Precipitation with Station CHIRPS and the Coordinated Regional Climate Downloading Experiment CORDEX projected rainfalls to establish the current and future water availability respectively. From the results, CV values ranging from 20 to 99% were obtained indicating that the region experiences moderate to high rainfall variability, often resulting in moderate to extreme floods and droughts in the area. The model simulations indicated that the stream-flows are increasing towards the 2020s decade compared to what was flowing in the 1980s decade, as observed between 1981 and 2020 using rainfall. This is probably a result of the increased rainfall observed in this region over the las four decades. Using Representative Concentration Pathways RCP 4.5 and RCP 8.5 projected rainfall scenarios, the model indicated that future stream flows will be higher than present. The findings show that, in the face of climate change scenarios, proper land management is required to promote water and food security in the drylands of sub-Saharan Africa in the future


K, RS, Mutham NJ, Opere AO, Opijah FJ, Gichuki FN.  2016.  Simulated Impacts of Climate Change on Surface Water Yields over the Sondu Basin in Kenya. Abstract

Potential impacts of climate change on surface water yields over the Sondu River basin in the western region of Kenya were analysed using the Soil and Water Assessment Tool (SWAT) model with climate input data obtained from the fourth generation coupled Ocean-Atmosphere European Community Hamburg Model (ECHAM4) using the Providing Regional Climates for Impacts Studies (PRECIS) model. Daily time step regional climate scenarios at a spatial grid resolution of 0.44˚ over the Eastern Africa region were matched to the Sondu river basin and used to calibrate and validate the SWAT model.
Analysis of historical and projected rainfall over the basin strongly indicated that the climate of the area will significantly change with wetter climates being experienced by 2030 and beyond. Projected monthly rainfall distribution shows increasing trends in the relatively dry DJF and SON seasons while showing decreasing trends in the relatively wet MAM and JJA seasons. Potential changes in water yields resulting from climate change were computed by comparing simulated yields under climate change scenarios with those simulated under baseline conditions.
There was evidence of substantial increases in water yields ranging between 88% and 110% of the baseline yields by 2030 and 2050 respectively. Although simulated water yields are subject to further verification from observed values, this study has provided useful information about potential changes in water yields as a result of climate change over the Sondu River basin and in similar basins in this region
Keywords: Simulated Impacts, Climate Change, Water Yields, Sondu Basin, Kenya

Kibe, RS, Muthama NJ, Alfred OO, Franklin OJ.  2016.  Assessment of Potential Changes in Hydrologically Relevant Rainfall Statistics over the Sondu River Basin in Kenya Under a Changing Climate . Abstract

Scenarios of past, present and intermediate future climates for Sondu River basin were analysed in this study to evaluate the potential changes in hydrologically relevant rainfall statistics that are likely to be observed by the middle of this century as a result of climate change. These climate scenarios were developed by applying dynamical downscaling of the relatively course resolution climate scenarios simulated by the fourth generation coupled Ocean-Atmosphere European Community Hamburg Model (ECHAM4) using the Providing Regional Climates for Impacts Studies (PRECIS) modelling system. The regional climate scenarios, which were available at a daily time-step and a spatial grid resolution of 0.5˚ over the Eastern Africa region, were matched to the Sondu river basin in the western region of Kenya. The possible hydrological impacts of climate change were assessed by applying the scenarios in a daily time-step hydrological model. The analysis of hydrologically relevant rainfall statistics focussed on determining changes in rainfall patterns and the likely hydrological implications to the basin. The results indicated that more rainfall is projected for the region in the immediate and intermediate future in form of increased seasonal rainfall during the December-January-February (DJF), March-April-May (MAM) and September-October-November (SON) seasons resulting from increased number of days of rainfall and higher probabilities of a wet day following a dry day in a month. Based on these scenarios, the combination of the wetter antecedent conditions and the more rain days in a month will result in more surface runoff being generated which will not only have implications on the water balance but also the water quality in the basin.
Key Words: climate change, climate scenarios, climate modelling, climate downscaling, Sondu Basin, Kenya



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