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Did rains do the Harappans in?

Author: Mihika Basu
Publication: The Indian Express
Date: June 3, 2012
URL: http://www.indianexpress.com/news/did-rains-do-the-harappans-in/957124/
 
Introduction: A New study provides compelling evidence that eastward migration of the monsoons created, then killed the Indus valley civilization

Between 3,900 and 3,000 years ago, the Indus Valley civilisation—one of the world’s biggest civilisations, the size of ancient Egypt and Mesopotamia put together—came to an end. Until now, there were no clear answers, only hypotheses. Did invading foreigners destroy the civilisation? Probably there were massive earthquakes that destroyed cities along the Indus and its tributaries? Or maybe the rivers simply shifted course and left the cities on their banks to decay? Now there is compelling evidence to show that it was climate change that led to the collapse of the earliest civilisation India has seen.

The findings, part of a new study titled ‘Fluvial landscapes of the Harappan civilisation’, were published in the Proceedings of the National Academy of Sciences last week. The study was conducted between 2003 and 2008 by an international team of scientists from US, India, UK, Pakistan and Romania with specialties in geology, geomorphology, archaeology and mathematics.

The study concludes that the slow eastern shift of the monsoons is what initially supported the civilisation by encouraging agriculture, but as the monsoon shifted further east, it weakened rain-fed rivers that were the lifeline of the civilisation.

“There have been numerous speculations until now about the links between this mysterious ancient culture and its life-giving rivers. We reconstructed the dynamic landscape of the plain where the Indus civilisation developed 5,200 years ago, built its cities, and slowly disintegrated between 3,900 and 3,000 years ago,” says Liviu Giosan, a geologist with Woods Hole Oceanographic Institution and the lead author of the study.

Prof Ronojoy Adhikari of the Institute of Mathematical Sciences, Chennai, who was part of the international team, says the work brings together several independent sources of data for the first time—sediments, topography, fluvial patterns, and archaelogical records—to provide “compelling” support for the climate change hypothesis.

“Our work shows that none of the earlier hypotheses—foreign invasion, rivers shifting course—is likely to be true. Rather, it was the shifting of the monsoon, which receded towards the north and the east of the Indian continent, that led to a drying up of the land in which the Harappans had made their civilisation and subsequently its collapse. This is the main finding our work,” he says.

The study also claims to resolve a long-standing debate over the source and fate of the mythical river, Sarasvati. Based on scriptural descriptions, it was believed that the Sarasvati was fed by glaciers in the Himalayas. Today, the Ghaggar, an intermittent river that flows only during strong monsoons and dissipates into the desert along the dried course of Hakra valley, is thought to best approximate the location of the mythic Sarasvati, but its Himalayan origin and whether it was active during Vedic times remain controversial. According to the team, the new geological evidence indicates that rivers were “indeed sizable and highly active” in this region, but most likely due to strong monsoons. The findings says that the “Sarasvati (Ghaggar-Hakra) was not Himalayan-fed, but a perennial, monsoon-supported watercourse and aridification reduced it to short seasonal flows”.

The paper says that like their contemporaries, the Harappans lived next to rivers, owing their livelihoods to the fertility of the annually watered lands. “Urbanism flourished in the western region of the Indo-Gangetic plain for approximately 600 years, but since approximately 3,900 years ago, the total settled area and settlement sizes declined, many sites were abandoned, and a significant shift in site numbers and density towards the east is recorded...The fluvial quiescence suggests a gradual decrease in flood intensity that probably stimulated intensive agriculture initially and encouraged urbanisation...further decline in monsoon precipitation led to conditions adverse to both inundation and rain-based farming,” concludes the study.

Over five years, the team studied satellite photos and topographic data collected by the Shuttle Radar Topography Mission, prepared and analysed digital maps of landforms constructed by the Indus and neighbouring rivers and corroborated this on the field by drilling, coring, and digging trenches.

The samples collected showed that around 5,200 years ago, settlements came up along the Indus as weakened monsoons and reduced run-off from the mountains “tamed the wild Indus and its Himalayan tributaries enough to enable agriculture along their banks”.

“The Harappans were enterprising people. The rivers were wild before the Indus civilisation started to appear. But as the monsoons and river floods started decreasing in intensity, agriculture started and gradually, the Indus became habitable and developed big cities,” says Giosan.

When researchers stumbled on this civilisation in the 1920s, they found evidence of sea links with Mesopotamia, arts and crafts and a still-to-be deciphered writing. The cities here, with Harappa being the largest of them, lasted for almost 2,000 years, but as the rains weakened, the monsoon-based rivers dried, leading to migration.

Giosan says the Harappans had an escape route to the east, towards the Ganges basin, where monsoon rains were more reliable. “There is a huge amount of archaeological work but it has never been linked properly to the evolution of the fluvial landscape. We now see landscape dynamics as the crucial link between climate change and people,” he says.

The team considers the findings a “lesson from the past”. “Today the Indus system feeds the largest irrigation scheme in the world. But if the monsoon were to increase in a warming world, as predicted by some, catastrophic floods such as the floods in Pakistan of 2010, would turn the current irrigation system, designed for a tamer river, obsolete.” says Giosan.

Adhikari says, “We need to step back and think much more seriously about how we must take care of our environment, or, we might face the same situation that our ancestors did in the Indus plains 4,000 years ago.”
 
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