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In Pragati: What caused the decline of Harappa?

(via Wikipedia)

(This was originally published in Pragati)

In The Wonder That Was India, A L Basham presented a dramatic picture of the decline of the Harappan civilisation. According to him, from 3000 BCE, invaders were present in the region. After conquering the outlying villages, they made their move on Mohenjo-daro. The people of Mohenjo-daro fled, but were cut down by the invaders; the skeletons that were discovered proved this invasion. Basham concluded that the Indus cities fell to barbarians “who triumphed not only through greater military prowess, but also because they were equipped with better weapons, and had learnt to make full use of the swift and terror-striking beats of the steppes.” Sir R Mortimer Wheeler claimed these horse riding invaders were none other than Aryans and their war-god Indra destroyed the forts and citadels at Harappa. But Basham was not that certain of the identity of the charioteers; he stated that they could be non-Aryans as well.

Basham wrote his book in early 1950s and a lot has changed after that. The decline of the Harappan civilisation is no longer attributed to “invading Aryans”, though that theory is still kept alive by political parties in South India. Even the non-Aryan invasion theory has been refuted as there is no trace in the archaeological record for such a disruptive event or the arrival of a new culture from Central Asia. The skeletons, which were touted as evidence for the invasion, were found to belong to different cultural phases thus nullifying the theory of a major battle. Due to all this, historians like Upinder Singh categorically state that the Harappan civilisation was not destroyed by an Indo-Aryan invasion. Instead of blaming the decline of the civilisation to invading or migrating population, the end is now attributed to environmental changes and whims and fancies of rivers.

From the late 1950s, historians believed that Mohenjo-daro was destroyed due to tectonic shifts in the region. According to one version, tectonic movements blocked the course of lower Indus river which must have caused floods that submerged the city. An opposing and the currently favoured theory suggests that instead of submerging in water, the city was starved of water. This happened because Indus shifted away from Mohenjo-daro, thus disrupting the crop cycle as well as the river-based communication network.

While Sindh, where Mohenjo-daro and Harappa are located, has just 9 percent of the 1140 Mature Harappan sites, the Ghaggar-Hakra basin has 32 percent of them; Archaeologists like S P Gupta and J M Kenoyer identify Ghaggar-Hakra with Sarasvati river. Around 1900 BCE, Kalibangan, located on the left bank of Ghaggar, was abandoned. Between the Mature and Late Harappan period, the number of sites along the river reduced considerably implying that the some hydrological change stopped the river from flowing.

One theory suggests that declining monsoons impacted water availability in Ghaggar-Hakra and that in turn caused the societal changes. Around 4000 years back, a dramatic climate change happened across North Africa, the Middle East, the Tibetan Plateau, southern Europe and North America. In India, during that period, there was an abrupt shift in monsoons, which lasted two centuries. In general, if you observe the patterns of recent years, monsoons have strong years and weak years, but they rarely deviate far away from the mean due to the dynamic feedback systems. It is a self-regulating system, but there have been occasions when the anomaly has lasted for few decades.

But what happened 4,000 years back was truly unusual; it was an anomaly larger than anything the subcontinent had faced since in the last 10,000 years. A paper published recently by Berkelhammer was able to narrow down the exact time frame during which this shift happened and it coincides with the decline of the Harappan civilization. This new study does not depend on indirect proxies (like pollen data), but uses a direct terrestrial climate proxy from the Mawmluh Cave in Cherrapunji and hence was able to show an unprecedented age constraint.

According to the paper, the most dramatic change occurred between 4071 (+/- 18) years and 3888 (+/- 22 years) Before Present (BP) for a period of 183 years. First there was a small rise between 4315 and 4303 years and a more precipitous one between 4071 and 4049 years BP. Once this change — which was earlier onset of monsoons or earlier withdrawal — happened, the monsoons stayed in this state for around 180 years before returning to normal values. Earlier monsoon withdrawal suggests that monsoon, which is tied to ocean-atmosphere dynamics and influences from the land surface, was weakened. For the Ghaggar-Hakra, which was fed by the monsoons, the impact was quite serious as it affected the habitability along its course. The study is quite interesting because it provides precise numbers for the duration and onset time for this climactic event. The previous studies did not have proper age constraints and some of them depended on factors (pollen, sedimentation rates) which could be influenced by external natural and man-made causes

Thus when one study claims that Ghaggar was a monsoon fed river and hence was easily susceptible to the vagaries of declining rainfall, there is another which shows that Sarasvati was a glacier-fed river and climate is not the only cause for changes. A paper in Current Science by K S Valdiya published in January of this year, titled The river Sarasvati was a Himalayan-born river, provides numerous counter arguments. First, the Sarasvati flowed through Western Rajasthan, which is one of the dustiest places on earth. 3500 years of dust storms have altered the landscape so much that the landforms created by the river would not be visible today. Second, the river ran through a region which saw tectonic upheavals and that would have altered the course of the river, like what happened to Indus. Third, the dimensions of paleochannels in the upper reaches of the river show that it was created by a large long-lived system. The paper strongly states that it was not a weakened monsoon, but the deflection of rivers by powerful tectonic activities which caused the decline of the Harappan civilisation along the Ghaggar river. Around 3,750 years Before Present, the Tamasa river joined Yamuna and a millennia later the Sutlej joined Beas. Due to this, the discharge of water in the Ghaggar was reduced and forced the Harappans to migrate elsewhere.

This is a contentious issue among academics; arguments and counter-arguments arrive sooner than you can digest them. While one controversy is over if tectonics or monsoon was responsible for the drying up of the river, there is another one over the climatic conditions during the Mature Harappan period. Some papers claim that Mature Harappan period occurred in a wetter phase and there are several others which show that Harappan urbanism rose in an arid phase. Paleoclimatology is a complicated field and more studies will give clarity to this controversy. But there is one certainty: the decline of the Harappan civilisation was not caused by invading Aryans or non-Aryans.


  1. Singh, Upinder. A History of Ancient and Early Medieval India: From the Stone Age to the 12th Century. 1st ed. Prentice Hall, 2009.
  2. Basham, AL The Wonder That Was India;: A Survey of the Culture of the Indian Sub-continent Before the Coming of the Muslims. 21st ed. Evergreen, 1977.
  3. Danino, Michel. Lost River: On The Trail of the Sarasvati. Penguin Books India, 2010.
  4. Berkelhammer, M, A Sinha, L Stott, H Cheng, F S R Pausata, and K Yoshimura (2012), An abrupt shift in the Indian monsoon 4000 years ago, in Climates, Landscapes, and Civilizations, Geophys. Monogr. Ser., vol. 198, edited by L. Giosan et al., 75–87, AGU, Washington, D. C., doi:10.1029/2012GM001207.
  5. Valdiya, KS “The River Saraswati Was a Himalayan-born River.” CURRENT SCIENCE 104, no. 1 (2013): 42–54.
  6. Giosan, Liviu, Peter D Clift, Mark G Macklin, Dorian Q Fuller, Stefan Constantinescu, Julie A Durcan, Thomas Stevens, et al. “Fluvial Landscapes of the Harappan Civilization.” Proceedings of the National Academy of Sciences (May 29, 2012). doi:10.1073/pnas.1112743109.


10 Responses to In Pragati: What caused the decline of Harappa?

  1. Suvrat February 20, 2013 at 1:25 am #


    regarding Valdiya’s paper- I am not at all impressed.


    He has provided no new data on the most crucial question of the provenance and timing of these paleo-rivers. His paper if full of misrepresentations, omissions and misattributions.

    Giosan et al. have already complained to Current Science.


    My criticism will be published in a forthcoming issue.

  2. Harappan Joe February 20, 2013 at 1:54 am #

    The paper by Berkelhammer provides no exact time frame for Harappa!

    It comes from Cherrapunji not from the Indus-Sarasvati region.

    Any serious monsoon scholar knows that the two regions are not in sync: when it is dry in Cherrapunji, it is wet in the Indus!

  3. jk February 20, 2013 at 6:28 am #

    Thanks Suvrat. One thing I noticed is that Valdiya’s article refers to non-public emails. That seems odd for a technical paper.

  4. Suvrat February 20, 2013 at 7:51 am #

    Yes, those are email communications between S. Kalyanaraman and Valdiya which Valdiya decided to go public with. He should have been more careful.

    • jk February 20, 2013 at 9:04 am #

      Right. Also the editors of journal should have paid more attention.

      One question for you: are the measurements from Cherrapunji a good indicator of monsoon patterns in the Indus region?

  5. Suvrat February 20, 2013 at 8:34 pm #

    regarding Berkelhammer’s study.. they do not try to directly provide a time frame for Harrappa as Harrappa Joe has commented. Instead they provided a tighter time bracket for changes in Indian monsoonal strength based on speleothems from Cherapunji. These timings concur with findings from other areas across Asia suggesting a wide spread change in the Indian monsoonal system around that time, including the Indus valley for which there are local indicators of drying.. Harappan decline has been independently dated, those dates as you pointed out coincide with Berkelhammer’s dates. So that the climate became drier by 2000 B.C. or so in this region is not at all controversial. All workers including Valdiya accept this ( he talks a lot about everything being buried by sand doesn’t he? :) ).

  6. Suvrat February 20, 2013 at 10:23 pm #

    just one more point that needs clarification. Harrappa Joe commented that monsoons in Harappan and Cherapunji are not in sync.. it may rain in Indus but not in Cherapunji. Indeed, but he is talking about a much finer time resolution of a few weeks to a couple of months. For example it may rain in Kerala but not in Delhi, but we still recognize that both these places are under the influence of the Indian monsoon system and that over the years there may be a trend of less or more rain at both places. It is the decline in strength of this system played out over a few decades to a few hundred years that Berkelhammer’s study addresses.

  7. Harappan Joe February 21, 2013 at 2:47 am #

    The dipoles in the monsoon between east and west of N India are active over many decades to hundreds of years indeed, not only for weeks or months. Read papers on ocean sediments, tree rings and caves deposits, Suvrat. They are not even so recent any longer!!!

    And findings across Asia are scant and badly dated. Besides they are not from the Indus, are they? So the kind of secondary indirect argument that should not be used unless you have a solid primary one!!!

    Not to talk about the changes in the Indus-Saraswati which have some of the worst chronology around… Berkelhamer’s study is good but applies to NE India only at this moment!!!

  8. Suvrat February 21, 2013 at 7:31 pm #

    thanks Harappa Joe for the clarification of your first comment..

  9. Kiran Batni February 24, 2013 at 12:00 am #

    Interesting article. Michael Wood’s BBC documentary, “The History of India”, also quotes climate change as the possible reason for the decline of Harappa. But note that this does not rule out the possibility of there having been an Aryan migration; it might just not have caused the downfall of the ancient civilization in the way we understand ‘the downfall of an ancient civilization’. Nor can the climate change theory obscure the fact of the ascendancy of the Aryan race following the decline of the original civilization.

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