Abstract:
As a country with an agriculture based economy, Sri Lanka has to pay more attention to
the climate extremes and variations in rainfall patterns. Evaluation of the regional variations
in rainfall patterns (especially in rainfall seasonality, severity and frequency of wet and dry
events) that reflect the trends in climate, is of essence for effective and sustainable
management of the available water resources. Therefore, the variations in rainfall
seasonality of Mannar District Secretariat Division (DSD), that lies within DL3 and DL4 agro
ecological zones of the dry zone was evaluated by devising the Gumbel approach. Daily
rainfall data for fifty three years (1961 to 2013) from the Mannar rain gauging station were
collected from the Department of Meteorology. Monthly cumulative rainfall values were
calculated and were subjected to a frequency analysis employing the Gumbel approach
under two major periods of calendar years as 1961 - 1985 (past years) and 1986 - 2013
(recent years), while considering the four rainfall seasons identified in Sri Lanka. The first
inter monsoon rainfalls indicated a reduction of the magnitude of low intense rainfall events
along with an increment in the return period of the intense rainfall events. Meanwhile, the
rainfall patterns in the second inter monsoon indicated an increasing trend of return periods
of high intense rainfall events in recent years than in past years. A declining trend in the
maximum average monthly cumulative rainfall and frequency of occurrence of intense
events of rainfall could be recognized in the Southwest monsoon and Northeast monsoon
periods in recent years (1986-2011) compared to the past (1961 to 1985). Thus, frequent
occurrence of severe and extreme dry events that could significantly affect both availability
and available quantity of water could be expected in Mannar, resulting in potential impacts
on environmental, economic and social sectors. Especially as a locality that often
experiences severe droughts, any further increment in the frequency of occurrence of dry
events (as predicted by the study) could significantly affect the economic, social and
environmental aspects. Therefore, timely planning and management of water resources in
Mannar, based on the observed present and expected future trends (increasing dryness)
in climate patterns (especially in rainfall pattern
