Smoothing of 70-year daily rainfall data based on moving average and weighted average technique

Abstract

An extreme value analysis of rainfall for Thanjavur town in Tamil Nadu was carried out using 70 years of daily rainfall data. Moving average method is a simple method to understand rainfall trend of the selected station. The analysis has been carried out for monthly, seasonal and annual rainfalls. No other graphical methods such as Ordinate graph, Bar diagram, Chronological chart will describe about the trend or cyclic pattern. By smoothening out the extreme variations and indicating the trend or cyclic pattern is known as moving average curve. Through this moving average curve, it is possible to understand the trend which can be used in the future years. From the results of annual wise rainfall analysis, based on 3-year, 5-year, 10-year moving average, it is found that there is no persistent regular cycle is visible and where as in 30-year, 40-year, 50-year moving average a horizontal linear trend has been observed. In Winter season, Summer season, North-East monsoon, South-West monsoon wise rainfall analysis, for 3-year, 5-year, 10-year moving average denote no apparent trend or cyclicity where as in 30-year, 40-year, 50-year moving average a horizontal linear cycle has been noticed. It is clear from the study that there is no large variation of rainfall that had been occurred in the Thanjavur city based on selected years of analysis.