Effect of climate change on monthly pond storage variation - a case study in Jaffna, Sri Lanka

Due to various anthropogenic interventions, the inherent natural function of water has been disturbed and distorted. Proper water management is vital to reduce flood damages and also to increase water availability in the dry season. The Jaffna peninsula in the northernmost part of Sri Lanka makes use of its existing pond systems to have an enhanced water functionality. However, due to the climate change, the rainfall pattern in the region has changed and currently, the peninsula is experiencing water scarcity especially during the dry period (January~September) while frequent flash floods occur in the wet season (October~January). The study attempts to determine the effect of rainfall pattern variability on pond water availability. Moreover, the study illustrates the variation of pond water availability using the Average Storage Index (ASI) during the study period of 16 years. Taking the monthly precipitation data for the period of 2002~2017, the pond storage variation of Paalkulam pond in the Jaffna Municipal Council (JMC) area was modelled. Monthly rainfall data, evaporation data, pond physical data and catchment data were used for this analysis. Pond simulations were carried out using the HEC-ResSim computer application. Whit the monthly rainfall data, the model simulation results show that the pond storage variation is becoming even critical during the dry period. The ASIs for 2002 are 0.681 and 0.996 for the dry period and wet period, respectively. However, for the year 2017, these indices change to 0.497 and 1.000. Study results show that due to the changes in rainfall pattern in the JMC area, the pond water availability is decreasing in the dry period. Furthermore, when looking at the yearly variation of ASI of Paalkulam pond, it clearly shows that the water availability is strongly driven by the precipitation to the peninsula. Therefore, for more adverse rainfall patterns, the water availability in the region would be much more serious. When the study results are taken into considerations, it can be concluded that the ASI of Jaffna ponds is getting decreased in the dry period due to the change of rainfall pattern which shows a noticeable reduction of water availability and rehabilitation and proper maintenance of pond storage play a critical role in addressing water scarcity issues