Analysis of rainfall distribution and variation during the Southwest monsoon in the wet zone of Sri Lanka

Abstract

The monsoon rainfall variation and distribution have an impact on economical, ecological and sociological aspects of Sri Lanka. Therefore, this research aimed to study the spatial-temporal variation and distribution of the Southwest monsoon rainfall during the period of 1981-2010. Daily rainfall data were collected from 13 rain gauge stations which are located in Southwest part (wet zone) of Sri Lanka. Monsoon rainfall distribution was analyzed by comparing monthly average rainfall and rainy days. The monsoon rainfall variability was analyzed using drought indices: Rainfall Anomaly Index (RAI) and Standardized Precipitation Index (SPI). Trend analysis was carried out on both indices considering the Mann-Kendall test and Sen’s slope estimator. Monthly average rainfall highlighted that the mid country experienced the highest amount of rainfall during the season and maximum number of rainy days occurred in the middle of the season. Analysis based on drought indices revealed that 14 years were dry. Both indices agreed on significant linear decreasing trends in rainfall at three rain gauge stations. Population growth, global warming, deforestation, etc., may be the reasons for these decreasing trends. These results create the need to discuss the economical, ecological and social impact of the rainfall which leads to better planning and rationalization.

Keywords

• trend analysis, mann-kendall test, sen’s slope estimator, southwest monsoon, rai, spi