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Spatial and Temporal Variability of Surface Water Flow in Sri Lanka

Author(s): Samarasuriya Patabendige Chaminda; So Kazama

Linked Author(s): So Kazama

Keywords: Distributed Hydrological Model; Surface runoff; Spatial and temporal variability; Monsoon rainfall; River basin

Abstract: Water needs to be protected and used in a sustainable way as water demand is extremely increasing. In per capita terms, Sri Lanka is well above the national water scarcity threshold of 1, 700m3 /person suggested by Falkenmark et al (1989). However at the local scale, already three districts are within the national water scarcity threshold as the Srilankan surface water availability varies significantly across 103 distinct river basins and four rainfall seasons. Many drivers including demographic pattern, economic growth and consumption pattern contribute to an increase and vary spatial and temporal water demand, have changed significantly since the early 1990s. Further, recent inconsistency of seasonal monsoon weather patterns has a major influence on surface water management system in the Sri Lanka. The present study aim is to analyze the changes in inter-annual and intra-annual spatial and temporal variation of surface water flow in the Sri Lanka to understand the surface water flow variation under the past climatic change. In this study, changes in annual and seasonal mean precipitation, maximum temperature and minimum temperature were analyzed between two time slices at 9 principle meteorological stations representing different climatic zones. The spatial characteristic of the study area is described by three base maps, i. e. land use, elevation and soil. Daily potential evapotranspiration was calculated by Hargreaves Equation and daily rainfall and evapotranspiration spatial maps were developed by inverse distance weighted interpolation method. Spatially distributed hydrological model was calibrated and validated for four different discharge gauge stations in four basins representing different climatic zones and soil types. Surface runoff for two different time slices was simulated for whole country using a validated model with different parameters to relevant basins. Further, Six basins were selected by representing different climatic zones to analyze the temporal variability of surface runoff. The results confirm that the annual mean minimum temperature has increased at most stations while maximum temperature has decreased at stations located in the wet zone. Seasonal mean maximum temperature shows the increase trend in the dry zone during southwest monsoon. Intra-annual runoff changes in basins completely located in dry zone are higher and mainly its’ runoff is limited to 2nd inter and northeast monsoons. Basins located in the west and east show significant increase in mean annual runoff volume due to precipitation increase in the southwest monsoon to the west and northeast monsoon to east. However river basins located in northwest show general decrease in mean annual runoff volume as inter monsoon precipitation gets reduced. It was confirmed that past climate change is significant in spatial and temporal variation of runoff over the country.


Year: 2013

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