Abstract
The downstream low lying region of the Kelani River including the Colombo suburbs, experience severe inundation due to heavy rainfalls in the upper basin of the Kelani River. Occurrence of heavy rainfalls is expected to be more frequent in the tropics with the impact of climatic change (IPCC, 2007). Therefore, understanding future rainfall intensity in the river basin and inundation in the low lying region along the lower reach of the Kelani River is extremely important as this is a region with a high population density and economic activities in the suburbs of the capital. The present study analyses the potential extreme rainfalls and resulting flood inundation along the lower Kelani River. Coarse grid atmospheric parameters provided by Global Climate Model (GCM) models for A2 (high emission scenario) and B2 (low emission scenario) scenarios of Intergovernmental Panel on Climate Change (IPCC, 2007) were downscaled to local scale by applying Statistical Downscaling Model (SDSM). Flood discharge and inundation along the Kelani River reach below Hanwella were analyzed by applying two-dimensional flood simulation model (FLO-2D). Inflow to the model at Hanwella, is estimated by the Hydrologic Engineering Center – Hydrologic Modeling System (HEC-HMS) model under future extreme rainfall events. Areas vulnerable to inundation under the above climatic change scenarios are presented.
Highlights
Climate change is defined as statistically significant variation in either mean state of the climate or in its variability, persisting for an extended period
According to the Disaster Management Centre (DMC), more than 38,000 families living in flood plains of Kelani River were affected during the 2008 flood [18], while more than 78,000 families were affected during the 2010 flood [17]
The results indicate that the model is capable of simulating discharge at the Nagalagam Street gauging station
Summary
Climate change is defined as statistically significant variation in either mean state of the climate or in its variability, persisting for an extended period (typically decades or longer). It has been predicted that the implications of climatic change on Sri Lanka are variations in rainfall patterns, sea level rise, and temperature [3]. This study discussed the frequencies of high intensity precipitation with their inundation extents in the Kelani River basin, produced under IPCC Special Report on Emissions Scenarios (SRES) A2 and B2 scenarios [16]. Both A2 and B2 emphasize on rapidly growing selfreliant nations while B2 accounts for more ecologically friendly growth. BScEng (Peradeniya), MEng, PhD (Uni. of Tokyo), Professor of Civil Engineering, Dept. SRTM DEM has been used in the hydrological modeling of upper Kotmale basin in Sri Lanka [6]
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