Anindya Sarkar, professor of geology and isotope geochemistry at IIT, Kharagpur, was lead researcher of a recent paper published in the Journal of Quaternary Science, on how Dholavira, an Indus Valley Civilisation (IVC) site, holds important lessons for dealing with climate change. The site was excavated by RS Bisht in the 1990s. Sarkar explains his study to Avijit Ghosh:

What does Dholavira mean? When and where did the site exist? When exactly was itspeak period?

Dholavira is the name of the village at Khadir bet, Bhachau Taluka, Great Rann of Kutch of Gujarat. “Bet” in local language means island. The archaeological (Harappan) site is locally known as Kotada timba meaning a large fort probably referring to the large ruins of the fortified ancient civilisation site.

The site is located about 500 meters north of the Dholavira village on the Khadir island within the low lying Rann of Kachchh. Our latest accelerator based radiocarbon dating suggests the beginning of occupation at least from 3500 years BCE (pre‐Harappan), and continuation until 1800 years BCE (early part of the Late Harappan period).

However, the settlement possibly started even earlier since the oldest settlement level could not be dated due to lack of datable material. One can guess that it can be even 4000 year BCE or even older making it a very ancient human settlement in the Indian subcontinent (“Pre‐Dholavira culture” named by the excavator Dr RS Bisht of ASI). The city expanded very rapidly from 2900 BCE till 2400 BCE when the inhabitants of Dholavira switched over from use of mud bricks to stone bricks for making houses and fortification walls; they built Citadel, Bailey, Lower and Middle Town much like what are found in most other contemporary cities like Harappa and Mohenjo‐Daro. These were probably due to social hierarchy where people from different segments of the society engaged in different activities used to live. During this peak period they added new architectural elements; their craftsmanship namely, making of potteries, ornaments rapidly improved and probably they started long distance trade with other Harappan/Indus valley civilisation sites even to Mesopotamia. This period in the context of Indus valley civilisation is known as urban Harappan period when it reached its acme.

What were the site’s distinct features?

Dholavira is the most spectacular IVC site in India and the fifth largest in the subcontinent in terms of areal coverage (Mohenjo Daro 250 hectare (Ha), Harappa 150 Ha, Rakhigarhi 80–105 Ha, Ganeriwala 81 Ha and Dholavira 70 Ha). It is the largest excavated Harappan site in India which can be seen by the tourists. All other sites were buried and covered up after the excavation was over. But Dholavira is unique because it records continuous settlement at one given place for over 1700 years from Pre‐Harappan to Late Harappan period. It shows excellent city planning, wide roads, architecture with geometric precisions, and craftsmanship. More importantly they adopted very advanced water conservation and harvesting system from building series of connected reservoirs, stone and terracotta drainage pipes to wells. They also built dams on the two rivers Mansar and Manhar which flowed around this city during this time. The dry river beds of these rivers can be seen even today. During this long period, the climate changed severely from a good monsoon to weak monsoon but they sustained these long years by adopting water conservation techniques suggesting their resilience and participatory nature of the society. The only thing that is yet to be studied is their burial history. Apparently there are burial mounds around but need to be excavated further by the Archaeological Survey of India and properly documented.

Dholavira is the fifth largest site of the Indus Valley Civilization. It is also the largest excavated site in India? Yet it is lesser known than say, Kalibangan. Why?

I do not know if such a comparison can be made. Kalibangan is located at southern bank of the presently dried river Ghaggar in Rajasthan and characterised by its unique fire altars and one of the world’s earliest ploughed field. But the features of Kalibangan and Dholavira are similar, similar town planning like citadel, lower town etc., and roads which had precision width. The timing is also almost similar from 3500 BCE to 1700 BCE after which both the cities collapsed. The only thing about Kalibangan is it was dated very extensively by archaeologists and its different phases were very well constrained by carbon dating. But after our work, Dholavira archaeological periods are also now on very strong ground in terms of its chronology. Dholavira is lesser known probably due to its remote location in the salt desert and also it was not studied until recently by using modern scientific techniques. In any case both were unique Harappan metropolis exhibiting very advanced city planning not found even in its counterparts in West Asia.

What caused the demise of Dholavira?

From the Later part of Mature Harappan time, i.e. from ~2400 year BCE the expansion of the city at Dholavira slowed down or even ceased until 2300 year BCE with an abrupt decline between 2300 and 2000 year BCE manifested by degeneration of architecture, craftsmanship, and material culture. They were unable to maintain the city; resources were scarce and water reservoirs were no longer in use. Also the site was deserted for few centuries. During the last Stage the city had disappeared, along with the classical Harappan elements and what remained had no resemblance to the Harappan culture. In a sense, it was an attempt to resettle at Dholavira but in a very basic way when probably the pastoralism re‐appeared who had no connection with the developed Harappan culture. Even this was for a very short period and the site was finally deserted. We feel the demise was connected to climate change. We analysed high resolution oxygen isotopes in mollusc shells Terebralia palustris. These are found aplenty in Dholavira, many of them are finely cut by human and were being consumed for food by the Dholavirans. These molluscs typically grow in mangrove suggesting that the people were harvesting them from nearby mangroves. The isotopes tell about the sources and the seasonality of water in which these animals grew. Surprisingly when we analysed the Early to Mature Harappan molluscs (2700 year BCE old) it looked that they grew in a water that is only possible if glacial meltwater mixes in the mangrove. The seasonality was high. This clearly suggested that a glacier fed river was debouching in the Rann of Kutch. But then isotopes in the molluscs from terminal part of mature to late Harappan from 2300 to 2100 years BCE indicated that the glacial contribution disappeared and seasonality reduced. This is the time that exactly coincides with the decadence and fall of the city of Dholavira as indicated by the archaeological evidence and the onset of the newly proposed Meghalayan stage (a divison of geological time) suggested last year by an international body of geologists and stratigraphers when a drought occurred across the globe. We could immediately make the connection. The monsoon was anyway declining. Dholavirans adopted excellent water conservation strategy by building dams, reservoirs and pipelines. But came the apocalypse of few centuries of Meghalayan drought and the whole city collapsed. The collapse of Harappan Dholavira was near‐synchronous to the decline at all the Harappan sites in India like Kalibangan, Lothal, Rakhigarhi as well as Mesopotamia, and the Old Kingdom of Egypt and China.

Your paper says, Dholavira presents a classic case for understanding how climate change can increase future drought risk across much of the sub‐tropics and mid‐latitudes? Please explain.

If you read all IPCC reports they predict increased frequency of extreme events including droughts in future due to impending climate change. The climate modelling studies suggest that in particular, drought will increase in sub‐tropics and mid-latitudes. We are beginning to see this in India. The number of monsoon break days is increasing while the number of monsoon depressions is declining. In 2019 a large part of our country was drought prone. All the past climate records in India show that monsoon was very strong between 7000 year and 5000 year BCE. From 5000 year BCE onward monsoon started declining, a record of which we published earlier from another Harappan site Bhiranna of Haryana. However, the monsoon was still higher compared to today. Scientists link this to solar radiation change that continuously reduced during this period. Clearly Harappans emerged at a time when monsoon was good and they sustained their cities by agriculture in fertile river banks be it Indus or Ghaggar‐Hakra around which almost all the Harappan sites grew. But then monsoon was decreasing yet the Harappans were genius to adopt water conservation as I told before. Not only this, they changed their crop pattern from water intensive crops like rice to millets which do not require so much water. This has been shown by many scientists including us from various Harappan sites. Just think about their modern outlook. Even today we cannot change the crop pattern in the drought prone areas with all our mighty technology, satellite surveys, and communications. The final blow to the Harappans, however, came when a global mega‐drought spread over over 2‐3 centuries hit them and they could no longer cope up. And as I said it was collapse of all the major ancient cityscapes across the globe. This seems like a fiction but it teaches us two important lessons. One is we must learn quickly how to cope up with the reduced monsoon and water deficit due to climate change specially our agriculture.Second if we do not learn then a catastrophe is waiting for us. The Dholavirans sustained for 1700 years and the modern civilisation is just about 200 years (if you consider industrial revolution). It is hard to tell what will happen after another 1500 years‐ will mankind survive or perish?

Union Finance Minister Nirmala Sitharaman referred to Harappan civilization as Saraswati‐Sindhu civilization in her Budget speech. Is that a historically accurate description?

Look Indus valley civilisation is a name given by archaeologists when it was discovered near Indus River. Because Harappa was a first type locality it was also called Harappan civilisation. This is customary in archaeology or geology to name a newly discovered time or event after the locality where it was discovered first. In geology when we say Devonian period it means a period that is 350 to 400 million years old, named after a place called Devon in England where it was first documented. But then Devonian rocks are found everywhere including Himalayas and geologists do not give it a different name because it is in India or Europe or Africa. These are accepted norms. Likewise when we say Indus valley civilisation it only means a period first described at places of Indus River valley.

But as we know now the civilisation was not only confined to Indus valley and in fact was far more expansive in India than thought before. And in India it grew along the Ghaggar‐Hakra river valleys which people often conjectured as courses of ancient river Saraswati mentioned in the Rig Veda. At present Ghaggar‐Hakra, though it originates in the Himalayas, is ephemeral and dries up at the periphery of the Thar Desert. Satellite imageries by ISRO scientists indicated that the palaeo‐channels of this river system probably flowed across the desert and into the Rann of Kachchh. Our isotope studies in the Dholavira molluscs provided first direct evidence of a glacier fed river that was debouching in the Rann of Kutch. Even today the river Indus has glacial meltwater contribution in its lower reaches. It has minor contribution from monsoon. Our data suggest that the Rann had periodic inundation of sea water where prolific mangroves grew and distributaries of Indus, like Nara (at Indo‐Pak border in Kachchh) or Saraswati like palaeochannels detected by satellite imageries in the southern margin of Thar Desert were dumping their water in the Rann. In that sense there is nothing wrong to call this civilisation as Saraswati‐Sindhu (Indus) civilisation. However this is a problem of semantics and archaeologists internationally have to agree about formal change to such name.