Protracted Indian monsoon droughts of the past millennium and their societal impacts

Abstract

Protracted droughts lasting years to decades constitute severe threats to human welfare across the Indian subcontinent. Such events are, however, rare during the instrumental period ( ca . since 1871 CE). In contrast, the historic documentary evidence indicates the repeated occurrences of protracted droughts in the region during the preinstrumental period implying that either the instrumental observations underestimate the full spectrum of monsoon variability or the historic accounts overestimate the severity and duration of the past droughts. Here we present a temporally precise speleothem-based oxygen isotope reconstruction of the Indian summer monsoon precipitation variability from Mawmluh cave located in northeast India. Our data reveal that protracted droughts, embedded within multidecadal intervals of reduced monsoon rainfall, frequently occurred over the past millennium. These extreme events are in striking temporal synchrony with the historically documented droughts, famines, mass mortality events, and geopolitical changes in the Indian subcontinent. Our findings necessitate reconsideration of the region’s current water resources, sustainability, and mitigation policies that discount the possibility of protracted droughts in the future.

On Indian Summer Monsoon Droughts and their Causal Mechanisms Over the Past Millennium

“…Indeed, the SOM analysis indicates that the number of La Niña events outnumbered the El Niño events by three to one margin and yet, this period emerged as one of the driest episodes of the past millennia as indicated by the PHYDA PDSI (Fig. 1) and historical textual evidence (8). We identified ten droughts over this period, of which nine were of non-El Niño type.…”

“…The statistical analyses of historical drought compilations from India have previously indicated the tendency of droughts to cluster within several decade-to-multidecade-length intervals over the past millennium (2)(3)(4)8). These clusters (red horizontal bars, below panel B in Fig.…”

Extreme local recycling of moisture via wetlands and forests in North-East Indian subcontinent: a Mini-Amazon

“…Like the Amazon, several studies have also documented worrying trends of declining forest cover and wetlands along with studies suggesting the change in regional precipitation patterns for North-east India 21 , 22 . Previous studies have attempted to explain the variability of the ISM rainfall with the help of speleothem-based oxygen isotope reconstruction in the region coupled with use of ISOGSM2 23 , 24 . Such approaches however are hindered by coarse spatial resolution of ISOGSM2 model, sparse availability of speleothem records as well as complex orography and moisture dynamics.…”

Dependence of fast changes in global and local precipitation on the geographical location of aerosol absorption

“…Precipitation is a crucial component of the hydrological cycle and many aspects of human society have evolved in response to the dynamics of regional precipitation (Kathayat et al 2022). Latentheat release through precipitation is an essential part of the atmospheric energy budget Hartmann 2012, 2014;Myhre et al 2017) and is balanced by changes in atmospheric radiative cooling and sensible heat fluxes on global-scales (Allen and Ingram 2002;Myhre et al 2018).…”