Abstract:
Inconsistency of seasonal monsoon weather
patterns during the past several decades have a major influence
on surface water management system in the in Sri Lanka. The
present study aim is to analyze the changes in the inter-annual
and intra-annual spatial and temporal variation of surface water
flow in Sri Lanka to understand the surface runoff variation
under the past climatic change. The spatially distributed
hydrological model was calibrated and validated for four different
discharge gauge stations in four basins and employed to simulate
the natural surface runoff over the period 1975 - 2005 at daily
time interval for 39 river basins. The rank-based, non-parametric
Mann-Kendall statistical test was used for trend detection due to
its robustness for non-normally distributed and censored data.
The results confirm that seasonal runoff changes in basins
completely located in dry zone are higher and mainly it is limited
to 2nd inter and northeast monsoons. Basins located in the west
and east show a significant increasing trend in mean annual
runoff volume due to precipitation increase in the southwest
monsoon to the west and northeast monsoon to the east. However,
river basins located in northwest show general decreasing trend in
mean annual runoff volume as inter-monsoon precipitation gets
reduced. This study concludes that wet zone basins get wetter
while leaving the dry zone drier during the past decades along
with climate change.
