Analysing temporal trends in the Indian Summer Monsoon and its variability at a fine spatial resolution

Abstract

Temporal trends between 1951 and 2007 in annual Indian Summer Monsoon (ISM) precipitation, frequency of severe drought years and onset date of ISM were analysed on a 0.25° × 0.25° grid cell basis across India using APHRODITE daily gridded precipitation data. Locations which experienced temporal trends of increasing or decreasing inter-annual variation in annual ISM precipitation and onset date of ISM were detected using the non-parametric Mann-Kendall test. A new method of defining local onset of ISM from daily precipitation data was developed to enable countrywide temporal trend analysis of onset date. India was characterised by a heterogeneous spatial distribution in the magnitude of inter-annual variation and location of significant temporal trends in the examined facets of ISM precipitation. A greater extent of the country experienced significant trends (p < 0.05) of increasing inter-annual variation rather than simple increasing or decreasing trends in annual ISM precipitation and onset date of ISM. Field significance tests showed grid cells reporting significant trends were significant (p < 0.05) at the global or field level (except trends of increasing, i.e. later, ISM onset date). This research provides finer spatial detail regarding trends and variation in annual ISM precipitation, severe drought years and onset date of ISM complementing recent studies on trends in extreme precipitation events over India to produce a comprehensive overview of recent behaviour of ISM precipitation. These findings will benefit water managers charged with managing water resources sustainably at a fine spatial scale (the watershed or basin level).