The 20th century transitions in basic and extreme monsoon rainfall indices in India: Comparison of the ETCCDI indices

Abstract

The mean and extreme matrices of the monsoon rainfall in India not only play an important role in depicting the global monsoon climate, but also their spatiotemporal patterns influence the socio-economic profile of a major proportion of the country's huge population. Given the reported conflicting trends at the global and national scales, the present study investigates the 20th century (1901–2004) changes in monsoon rainfall of India, particularly focusing the indices developed by the Expert Team on Climate Change Detection and Indices (ETCCDI) to facilitate a global comparison. Result of this comprehensive analysis, which includes the response of fifteen indices over two study periods (i.e., 1901–1940 and 1961–2004), indicates clear signals of change with respect to the period and region of study and the choice of the ETCCDI indices. While wet day frequency, low-tomoderate events and consecutive wet days (CWD) exhibit a prominent transition from a pre-1940 wetting to a post-1960 drying tendency over a large part of the central-north India (CNI), both the wet and dry extremes have occurred in a spatially less consistent manner during the recent decades. For consecutive dry days (CDD), the reported less clear global signals could be related to the timescale of analysis, as our sub-seasonal scale results Display consistent changes compared to that of the seasonal and annual scales. The Palmer Drought Severity Index (PDSI) provides clear indications of a post-1960 non-stationarity, showing changes in the mean as well as variance. Based on the partial Mann–Kendall test (PMK), some of the identified rainfall trends during 1961–2004 are found to be influenced more by the tropical Indian Ocean sea surface temperatures than the El Niño–Southern Oscillation index. These results have important implications for formulating the water resource management strategy, particularly over the drying central and northern parts of the country.