Implications of palaeohydrological proxies on the late Holocene Indian Summer Monsoon variability, western India

In this paper we identify changes in the Indian Summer Monsoon (ISM) intensity during the late Holocene as revealed by palaeohydrological proxies in the fluvial archives of western India. Proxy indices, including the geomorphological, sedimentological, geochemical and biological evidence along with chronology have been employed to highlight the trend in ISM intensity over the late Holocene. It is inferred that on a longer timescale, the Indian Summer Monsoon weakened during the late Holocene however; short pulses of ameliorated monsoon occurred around 3, 1.6 and 0.3 cal ka BP. Clustering of flood events is seen to occur at 3-2.8, 2.2-1.6, 1.3-1.1 and 0.65-0.2 cal ka BP not necessarily coinciding with strengthening of the ISM. Palaeoflood data with regard to the ISM variability shows that the two most prevalent flood events at 0.5 and 1.7 cal ka BP coincide with the weak monsoon period/climatic transition in this region. The occurrence of high magnitude flood events during weak monsoon periods is also reflected in the modern flood and rainfall data. It is surmised that high magnitude flood events may represent peak monsoon periods however, cannot be singularly considered as indicators for enhanced monsoon conditions in a region. Only a more robust database of palaeohydrological proxies can further validate their implications on the monsoonal changes over western India.