Seasonality Index

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6.2 The Seasonality Index As stated earlier, this study focused on analyzing the variability and seasonality of rainfall in 34 sub-divisions inside India. At first, individual seasonality index was calculated that provides information about the inter-annual variations in seasonality and then, mean individual seasonality index was calculated. Variability in SI was measured using the coefficient of variability. Fig.4 : SI and total variability in a) annual rainfall and b) Jun-Sept rainfall All the sub-divisions receive most of the rainfall during monsoon months with varying time period. Therefore, SI (monsoon) value varies from 0.19 over Nagaland-Manipur-Mizoram-Tripura sub-division (Table 2) in the…show more content…
The maximum SI value (> 1.20) recorded by five sub-divisions, viz. East Rajasthan; West Madhya Pradesh; Gujarat Region-Dadra & Nagar Haveli; Saurashtra-Kutch & Diu and Konkan & Goa (Fig.6) also show extreme seasonality over these sub-divisions. Many a times these sub-divisions experience heavy rains just in one or two months during the monsoon season. The lowest SI value of 0.59 over Jammu & Kashmir indicates that the rainfall over this sub-division is purely seasonal. This rainfall is rather generated by local convection due to western disturbances at higher elevations along with the synoptic scale systems moving at the foot hills of Himalayas. Seasonality Index was computed for all the 34 sub-divisions inside the country for the entire period 1951-2015 as well as for two different periods, viz. 1951-2000 and 2001-2015 in order to know whether there is any change in SI during the last 15 years and previous 50 years period (Fig.6). Fig. 6: Variation of SI during 1951-2000 and 2001-2015 for 34

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