DISTRIBUTION AND FUTURE TRENDS OF MONTHLY RAINFALL IN THE DISTRICTS OF KERALA – A STATISTICAL APPROACH
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Date
2017
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Acharya N.G. Ranga Agricultural University
Abstract
An attempt was made to study the district wise monthly rainfall pattern of Kerala
State. Data pertaining to monthly rainfall of the fourteen administrative districts of the
state starting from 2004 to 2016 (156 months) was collected from Regional
Meteorological Centre, Thiruvananthapuram for the study. Components of time series
viz., secular trend, seasonality, cyclical variation and irregularity were studied along
with the descriptive statistics like Arithmetic Mean (AM), Standard Deviation (SD) and
Coefficient of Variation (CV%). To determine regional rainfall pattern, a non
hierarchical cluster analysis, i.e., K means Clustering Algorithm, was applied on
autocorrelation coefficients at different lags and four rainfall groups were found based
on the time series models. The results of the time series modeling showed a high
variation of temporal pattern of the monthly rainfall over Kerala. Auto Regressive
Integrated Moving Average (ARIMA) models, Seasonal Dummy models and Seasonal
Exponential Smoothing were fitted to the data and best model was chosen based on
values of AIC, SBC, R square and MAPE. Better forecasts were obtained by Seasonal
Dummy and Seasonal Exponential Smoothing.
Trend analysis showed that the mean monthly rainfall of Kerala State exhibited a
slightly decreasing trend over the period of study and seasonal indices were found
highest in June and least in January. Clustering of districts showed that Kasargod and
Kannur districts were listed under cluster 1 while Thiruvananthapuram was listed under
Cluster 2 alone. Kottayam, Alappuzha, Pathanamthitta and Kollam were listed under
Cluster 3 while Kozhikkode, Wayanad, Malappuram, Palakkad, Thrissur, Ernakulam
and Idukki were listed under Cluster 4.
The results of descriptive statistics indicated that the state received consistent
rainfall in the month of June and inconsistent rainfall in February month. It also
revealed that the state received maximum rainfall in 2007 and least rainfall in 2016
during the study period.
Description
D5458
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