Indus-Saraswati Civilization: The weakened monsoon theory

What caused the end of the Indus-Saraswati civilization? There are many theories regarding this

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 Indradestroyed 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.[In Pragati: What caused the decline of Harappa?]

Marxist historians now say that there was no Aryan Invasion, but there was migration.  One theory says that tectonic events altered the course of the rivers causing the decline of the civilization.  Another says, the decline was caused by weakening monsoons. But can climate change be the primary cause?
The weakening monsoon theory is not new.

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.[In Pragati: What caused the decline of Harappa?]

Here is another one

The Arabian Sea sediments and other geological studies show that the monsoon began to weaken about 5,000 years ago. The dry spell, lasting several hundred years, might have led people to abandon the Indus cities and move eastward into the Gangetic plain, which has been an area of higher rainfall than the northwestern part of the subcontinent.

“It’s not high temperatures, but lack of water that drove the people eastward and southward,” Gupta said [Indus cities dried up with monsoon]

Now animal bones from Bhirrana have provided clues regarding the decline of the Indus-Saraswati civilization. To appreciate this better, we have to know where Bhirrana is and its significance.

Map from Oxygen isotope in archaeological bioapatites from India: Implications to climate change and decline of Bronze Age Harappan civilization

Look at where Kalibangan and Dholavira are. Kalibangan is on the left bank of Ghaggar and is located at the confluence of Saraswati and Drishadvati. Dholavira is at the Rann of Kutch, which is not really a place where you want to settle down. There was a reason the people of Indus-Saraswati civilization did so: during the Mature Harappan times, people of Dholavira had access to the sea. If you trace the path of the Saraswati Paleochannel, you will see the connection between the two places. Also, if you trace the paleochannel towards  north of Kalibangan, you will see Bhirrana.

 The Ghaggar (in India)-Hakra (in Pakistan) river, referred to as mythical Vedic river ‘Saraswati’ (Fig. 1A) originates in the Siwalik hills, ephemeral in the upper part with dry river bed running downstream through the Thar desert to Rann of Kachchh in Gujarat3. More than 500 sites of Harappan settlements have been discovered in this belt during the last hundred years. Of these several sites both in India viz. Kalibangan, Kunal, Bhirrana, Farmana, Girawad and Pakistan viz. Jalilpur, Mehrgarh in Baluchistan, Rehman Dheri in Gomal plains have revealed early Hakra levels of occupation preceding the main Harappan period.[Oxygen isotope in archaeological bioapatites from India: Implications to climate change and decline of Bronze Age Harappan civilization]

Here is the impressive fact about Bhirrana: it is currently the oldest settled site in the Indian subcontinent. It was settled from around 7000 BCE and is located close to the Saraswati river bed.  It was not an urban civilization at that point. Like the other Harappan sites, it started out as pastoral and later had major farming communities. Eventually, the people there developed the usual Harappan urban entities: mud-brick houses, sacrificial pits etc.
A recent paper analyzed the drinking water component inside animal bones of cattle, goat, deer and antelope from Bhirrana. This was compared against the monsoon levels in the Arabian Sea and carbonate levels in two inland lakes close to Bhirrana. While monsoons intensified from 7000 BCE to 5000 BCE, it declined from then.  This correlates with data available from other sites in Asia. When such an event happens, it affects rivers like the Saraswati and the sites along its banks. That did not cause the end of Bhirrana; it continued and thrived for while. The residents of Bhirrana changed their crops to adapt. From wheat and barley, they switched to drought-resistant millets and rice.

 Because these later crops generally have much lower yield, the organized large storage system of mature Harappan period was abandoned giving rise to smaller more individual household based crop processing and storage system and could act as catalyst for the de-urbanisation of the Harappan civilization rather than an abrupt collapse as suggested by many workers. Our study suggests possibility of a direct connect between climate, agriculture and subsistence pattern during the Harappan civilization. .[Oxygen isotope in archaeological bioapatites from India: Implications to climate change and decline of Bronze Age Harappan civilization]

What this means is that the end was not sudden. It was slow. Rain reduced. Rivers did not get the rains it once got. The boundless, impetuous and swift-moving Saraswati which once flowed till the sea, no longer did so. Maybe there were tectonic movements which caused the rivers to go haywire and forced people to move elsewhere.

The Harappan angulam

(Sudama and Lomas Rishi Caves at Barabar, Bihar, in 1870)

During the time of Emperor Asoka and his successor Dasaratha, seven caves were constructed in Barabar and Nagarjuni hills, about 47 km from Gaya; during the Mauryan times, these hills encircled the city of Rajagriha. In the thirteenth year of his reign Asoka donated two caves in Barabar hills to Ajivikas. He donated one more in the 20th year of his reign while the Third Buddhist Council was going on, and all these were documented carefully with inscriptions inside the cave. The caves in Nagarjuni hills were the work of Asoka’s successor – his grandson Dasaratha – and these caves, like the ones in Barabar hills were donated to the Ajivikas[5].
These caves had circular roofs and the surfaces were polished. When these caves were measured, it was found that they were not constructed to random dimensions, but to a well known measure from the Harappan period: the angulam[2].
The urbanized Harappan civilization with elaborate town planning had knowledge of geometry and standardized measures. Statistical analysis of various Harappan settlements has shown that the basic unit of measurement was 17.63 mm[3]. This is taken to be one angulam and 108 angulams one dhanus. Various dimensions in the Harappan site of Dholavira are  integral multiple of dhanus. Now at a different site — Kalibangan — a terracota scale was found and when the measure between the tick marks was analyzed, it was found to be 17.5 mm. This also matched the measurement found in ivory and metal scales and shell markings at other sites[1].
The angulam is approximately 1.763 cms in Harappa, 1.75 in Kalibangan, and 1.77 in Lothal. The Arthashashtra derives larger units from angulam: garhapatya dhanus is 108 angulams; 1 danda, 96 angulams.
In the Mauryan caves, it was found that the danda measured the cave perfectly. For example the Lomas Rishi cave was 6 dandas long and 3.5 dandas wide and the Sudaman cave, 10 dandas long and 3.5 dandas wide. There is some fine print here as the Arthashastra provides confusing descriptions for various measures: one hasta is either 24, 28, or 54 angulams and one danda is 96 or 192 angulams. Since 96 was used by later texts, that measure was chosen.
What makes this interesting is that while cutting caves through hard rock, the Mauryans did not randomly dig through; the caves were carefully planned and constructed with pre-determined dimensions. Two caves in  Nagarjuni hills had the same dimension, so did two caves in Barabar hills. This also reveals that the Harappan measures were used in the Gangetic plain, even after 2000 years.


  1. Analysis of terracotta scale of Harappan civilization from Kalibangan, Current Science, VOL. 95, NO. 5, 10 September 2008, R. Balasubramaniam, Jagat Pati Joshi
  2. New insights on metrology during the Mauryan period by R. Balasubramaniam in Current Science, VOL. 97, NO. 5, 10 September 2009
  3. Unravelling Dholavira’s Goemetry by Michel Danino
  4. New Insights into Harappan Town-Planning, Proportions and Units, with Special Reference to Dholavira, by Michel Danino, Man and Environment, vol. XXXIII, No. 1, 2008, pp. 66-79
  5. Asoka and the Decline of the Mauryas by Romila Thapar

Image Credit: Wikipedia