Analysis of weekly rainfall of different period during rainy season over Safdarjung airport of Delhi for 20th century – A study on trend, decile and decadal analysis

Abstract

The analysis of weekly rainfall and of different period during rainy season of Safdarjang airport using techniques like trend and decile have been attempted. Decadal analysis is also attempted to see any changes during the entire period. Rainy season is defined as rainfall received from week no. 23rd to 38th. Weekly rainfall data for period 1901 to 2000 is utilized for this location. As week is a shorter period to analyze rainfall for the season groups of different periods consisting of 4 weeks such as 1-4 as ‘A’, 5-8 as ‘B’ and so on up to ‘D’ is formed. For study of progressive season combination of groups such as ‘A+B’, A+B+C and ‘A+B+C+D’ are also subjected to analysis as done for weekly as well for group.

The average weekly rainfall distribution indicates very high positive value of coefficient of correlation (0.94) significant at 1% level. The coefficient variation (C.V.) of weekly average rainfall shows consistency from decade 5th to 8th and 10th. Profile of average C.V. of weekly rainfall for 100 years shows consistency from week 4 to 11. Week no. 8 shows peak of rainfall. Overall decile analysis of weekly rainfall shows increasing tendency from week no. 1 to 8 for all deciles and then decreasing tendency from week no. 9 on words for all decile values. Trend analysis of group ‘C’ shows significant positive tendency with correlation as +0.20 significant at 5% level. However trend analysis of deciles of all groups shows very high C.C. around +0.95 at 1% level. Trend analysis of combination of groups shows positive trend for A+B+C and for A+B+C+D with a C.C. of 0.25 and 0.20 at 5% level. Trend of deciles for these groups also shows very high C.C. values around +0.95 at 1% level. Average, excess and deficient rainfall seen at Safdarjung airport is 5th, 7th and 4th decile with values as 594, 708 and 472 mm respectively. Analysis of two halves of century, viz., 1901-50 and 1951-2000 shows no significant trend.