Detecting Changes in Annual and Seasonal Rainfall Patterns for Chennai, India

Abstract

The northeast and southwest monsoons control the climate of the city of Chennai. Rainfall analysis with an emphasis on drought using the precipitation data of 115 years (191–215) was done to quantify the trends. The trend is analyzed annually and seasonally, which revealed a nonsignificant increasing trend in annual rainfall and a significant decreasing trend in winter. The rainfall is irregular and is confined to the latter half of the year, with the maximum contribution occurring in just three months. Several indexes and drought indicators were used for the temporal analysis and for the quantification of the severity of the rainfall and drought events. The precipitation concentration index (PCI) values point to irregular rainfall distribution in almost 84% and a large monthly variability in 38% of the years studied. The magnitudes of the northeast and southwest monsoons are in opposition. The values of the Seasonality Index (SI) signify that most of the rainfall is concentrated in few seasonal months with a prolonged dry season. The rainfall concentration is greatly correlated with the drought pattern. The Rainfall Anomaly Index (RAI) values indicate that out of 115 years, there were five extremely dry and four extremely wet years.