Recurring summer and winter droughts from 4.2-3.97 thousand years ago in north India

Abstract

The 4.2-kiloyear event has been described as a global megadrought that transformed multiple Bronze Age complex societies, including the Indus Civilization, located in a sensitive transition zone with a bimodal (summer and winter) rainfall regime. Here we reconstruct changes in summer and winter rainfall from trace elements and oxygen, carbon, and calcium isotopes of a speleothem from Dharamjali Cave in the Himalaya spanning 4.2–3.1 thousand years ago. We find a 230-year period of increased summer and winter drought frequency between 4.2 and 3.97 thousand years ago, with multi-decadal aridity events centered on 4.19, 4.11, and 4.02 thousand years ago. The sub-annually resolved record puts seasonal variability on a human decision-making timescale, and shows that repeated intensely dry periods spanned multiple generations. The record highlights the deficits in winter and summer rainfall during the urban phase of the Indus Civilization, which prompted adaptation through flexible, self-reliant, and drought-resistant agricultural strategies.

Borneo Stalagmite Evidence of Significantly Reduced El Niño‐Southern Oscillation Variability at 4.1 kyBP

“…MacDonald (2011) previously hypothesized an ISM-ENSO relationship when interpreting monsoon rainfall records related to the Harappan civilization through the Holocene. We note that recent, robustly dated proxy records which record both ISM and Indian Winter Monsoon (IWM) strength in the Indus River valley are interpreted to indicate a weaker ISM and IWM from 4.0 to 4.2 kyBP, and a stronger ISM from 3.6 to 4.0 kyBP (Giesche et al, 2019(Giesche et al, , 2023. The strong ISM from 3.6 to 4.0 kyBP does not reflect a negative correlation with the Borneo record's suggested high ENSO variability (strong El Niño events) beginning around 4.0 kyBP, highlighting the complex nature of and likely multiple influences on ISM strength across India, apart from just ENSO.…”

Forgotten Islands of the Past: The Archaeology of the Northern Coast of the Arabian Sea

“…The study of the finds has improved our knowledge of the peopling of this part of the northern coast of the Arabian Sea between the Neolithic and the Bronze Age, roughly from middle of the 5th to the end of the 3rd millennium cal BC (Biagi et al, 2018). Important information has been gathered about the period during which climatic conditions like those of the present day started to be established, and the Indus Civilisation went into decline (Clift & Giosan, 2018, p. 24;Giesche et al, 2023;Staubwasser et al, 2003).…”