The climate is one of the conspicuous topics in the world at the moment because of the changes that have occurred in it and the deviations that it is showing right now. Changes in precipitation are one of the prominent ways to identify the climate changes because those variations in the rainfall are the basic symptoms of disastrous end results of the climate change. So the prediction of rainfall is so crucial from that point of view and another set that massively affected by this are the countries which have rain-fed agriculture-based economic system because they might have to their adaptation strategies against upcoming changes in precipitation. So the world has moved to analyse the precipitation changes and lots of research work have been done locally and internationally considering various analysing methods using hourly, monthly and annual rainfall intensities and depth data. Analysis of data over a series of years at least 30 years back considering time trends has shown prominent effects on design rainfall events previously. The results obtained from these research work show that there are actually identifiable time trends in rainfall patterns and another thing that has revealed is that these trends can only be identified for some areas and the trends are varying from one region to the other. Most of the results all around the world highlight that the rainfall intensities have been increased while the duration has been decreased. So likewise this research is focussed on the identification of time trends in Rathnapura rainfall pattern and determination on the impacts on design rain events of that area.
Keywords: climate; precipitation; trends; Rathnapura; events; patterns
Water is one of the basic needs of all living beings. Rain is one of the main sources that the world gets fresh water. So the existence of the world massively depends on the rainfall. There are lots of factors which affect the precipitation throughout the world. Amount of the tropical rainforests that are present in the world is one of the main factors among them. Though the rainfall is unpredictable, with the continuous uncontrolled deforestation that has been happening all around the world and because of the other governing factors the rainfall or the precipitation seems to be showing a bit different behaviour which was not seen in the past. This kind of differences in rainfall could be the symptoms of huge climatic changes and these changes could affect the world extremely. So for the developing countries like Sri Lanka, it would be better to have rather accurate and dependable forecasting systems that can tackle even small changes and patterns in rainfall spatially and temporally.
Sri Lanka is an island in the Indian Ocean which is located at the southern tip of the Indian subcontinent extend between 5°55′ and 9°50′ N and between 79°41′ and 81°53′ E. Because of this location, the rainfall climate of the country is being governed by the Indian Ocean monsoon system. Mainly the country receives rainfalls under two principal monsoon seasons (south-west and northeast) and two inter-monsoon seasons (First inter-monsoon and second inter-monsoon) in different time periods throughout the year (Burt & Weerasinghe, 2014). According to the spatial annual precipitation, two main climatic zones can be identified in the country which extends to the west side and the east side from the central hills as wet zone and dry zone respectively (Malmgren, Hulugalla, Hayashi, & Mikam, 2003).
Rathnapura is one of the cities in the wet zone in Sri Lanka which receives rainfall throughout the year with an annual average precipitation of 3922.6mm. Mainly Rathnapura gets heavy showers due to south-west monsoon between May to September and due to second inter-monsoon between October and November. Normally maximum rainfall is recorded in May and minimum rainfall is recorded in February (Ampitiyawatta & Guo, 2010). Hence the rainfall plays a significant role in day to day life in this part of the country it’s very important to design rain events for the area rather accurately because the life will depend on a lot and most importantly the Rathnapura area is situated in a floodplain of Kalu Ganga. Since up to now in Sri Lanka the rain forecasting was done without considering trends in time in the rainfall pattern now it’s the time to use an advanced method to analyse the rainfall data with the impact of temporal trends and it will lead to better designs of rainfall events.
2.1 Climate change
Climate change is the most pressing issue at the moment in the world. The reason why this issue becomes this much important is the adverse impacts that have been affecting the world since the beginning of the 21st century. For an example; between 1998 and 2001 because of the floods in European rivers 700 deaths, half a million displacements and a waste of 25 billion worth economic losses were reported (Thielen, Bartholmes, Ramos, & de roo, 2009). From the research, it has found that the main reason for the climate change is the global warming. The emission of greenhouse gases which has been increased with the industrial development is the main source of the greenhouse effect and it is the main reason for the increment of the temperature. The other main thing which is related to this issue is the hydrological cycle with extreme rainfalls and drought, melting of glaziers ETC. With the current extreme events that are happening, we can easily identify that the climate change has already effected on it