Identification of changes in rainfall pattern in paddy growing areas in Sri Lanka: A case study in Anuradhapura district

It is now widely accepted that the global climate is changing with increasing greenhouse gas concentration in the atmosphere due to human activities. There is enough evidence for more negative impacts of climate change on world agricultural sector. As an agricultural country, Sri Lanka is also experiencing some inevitable consequences due to changing rainfall onset, distribution and the amount. Standardized Precipitation Index (SPI) is a drought monitoring index which is developed for identifying rainfall anomalies with respect to the past data in the same location for specific time scales. The aim of this study was to identify the changes in rainfall patterns using SPI in Anuradhapura district which is one of the major paddy growing areas in Sri Lanka. Monthly rainfall data were collected from four Meteorological Stations viz, Anuradhapura, Maha Iluppallama, Maradankadawala and Kebithigollewa for the period of 1980-2018. Five months SPI values were computed to represent Yala & Maha cultivation seasons and 12 months SPI values were computed to represent the annual rainfall anomalies. Mann Kendal Test was used to identify the trends in selected SPI time series. The results of the study revealed that, there are significant increasing trends in total annual rainfall in Anuradhapura district indicating low risk of having drought years in future. The significant increasing trend in SPI values in Yala & Maha seasons in both Anuradhapura and Maha Iluppallama stations imply that there is a high chance of receiving enough water for cultivation in both seasons in near future. Further, a significant decrease could be observed in total annual and Yala season’s SPI values in Maradankadawala indicating a high potential of having droughts. However, Kebithigollewa does not show any significant change in total annual, Yala or Maha seasons rainfall patterns. Finally, it can be concluded that, as Anuradhapura, Maha Iluppallama and Kebithigollewa areas are getting slightly wetter, the paddy cultivation in the Western and Southwestern areas of Anuradhapura district would not be severely affected due to changing rainfall patterns. However, as Maradankadawala area is getting slightly dryer with the changing rainfall patterns, strengthening water conservation techniques would be better for paddy cultivation in the Southeastern area of Anuradhapura district in order to adapt to the incoming dry periods.