Decadal frequency and trends of extreme excess/deficit rainfall during the monsoon season over different meteorological sub-divisions of India

Abstract

The monsoon season (June–September) is the major source of rainwater in all the meteorological sub-divisions of India, except the Tamil Nadu & Pondicherry sub-division. In this study, the observed trends in monsoon rainfall, monthly as well as seasonal, were investigated and compared, and the variability and frequency of extreme excess and deficit rainfall during 1871–2008 were also analysed. The magnitude of a trend was estimated using Sen's slope method. The trend results, using the Mann-Kendall and Spearman's Rho trend tests, were similar for all the 30 meteorological sub-divisions of India, as well as for the Indian region, for monsoon months and for the monsoon season. In the majority of sub-divisions, a decreasing trend of monsoon rainfall during the study period was found. The decadal trends in frequency and the spatial variability of occurrence of extreme excess/deficit rainfall years were also investigated. The results show that the decadal occurrence of number of extreme excess rainfall years over the eastern coastal sub-divisions has an increasing trend, while 17 sub-divisions show decreasing trend. However, the occurrence of total extreme deficit rainfall years shows an increasing trend over the eastern and peninsular sub-divisions, except for Kerala and Gangetic West Bengal. Citation Subash, N., Ram Mohan, H.S. & Sikka, A.K. (2011) Decadal frequency and trends of extreme excess/deficit rainfall during the monsoon season over different meteorological sub-divisions of India. Hydrol. Sci. J. 56(7), 1090–1109.