Indus Valley Civilisation flourished along the course of river Indus and was one highly depended on a perennial water source for sustenance.
While there are varying claims on civilisation’s climate, a recent research has asserted that the civilisation was at its peak during its wettest phase.
What is Indus Valley civilisation (IVC)?
Indus Valley civilisation (IVC) is one of the earliest known organised urban human settlements, which flourished around 2000 BCE.
It flourished in the north-western parts of the Indian subcontinent, in the region around north Rajasthan, Haryana, Punjab, and Pakistan.
Its settlements are estimated to have flourished for 1,500 years between 3000 and 1500 BCE, and is said to have had its zenith between 2600-1900 BCE.
Those glorious 700 years is when the most modern townships of that era namely - Harappa, Mohenjo-daro, and Rakhigarhi is said to have flourished.
The decline of the IVC is attributed to several reasons - climatic, tectonic, and even social – all of which have varying degrees of evidence to support them.
How critical was water in IVC’s progress?
Most scientists and archaeologists agree that the availability of abundant water was the most crucial enabler for the sustenance of the civilisation – just like most other contemporary ancient civilisations.
The presence of buried water channels and other archaeological evidence suggests the dependence of Indus people on a perennial source of water.
Many geological and climatic studies have indicated good rainfall patterns in IVC region during the civilisation’s existence (although some disagree).
What did the researchers rely on?
Gypsum deposits at an ancient lake “Karsandi” (now dry) on the margins of the Thar Desert in northern Rajasthan were studied by the researchers.
Notably, Karsandi is about 120 km northeast of Rakhigarhi, an important IVC settlement that has seen some exciting excavations very recently.
It is also near Kalibangan and Karanpura, which were also important centres of the Indus civilisation.
The scientists collected samples of different layers of gypsum and studied them in detail and carbon dated the fossils in them to establish dispositional age.
While many such paleo-lakes in the region have been studied before, this is the first time that scientists were able to devise a chronology of rainfall variations.
This analysis has asserted a clearly asserted that rainfall had a bearing on the expansion and contraction of Indus urbanism (more rain more prosperity).
What is the concept employed?
Chemical analysis of the layers of deposites in a paleo-lake gives indications about the composition of water at different times.
It thereby also gives indications on the environmental condition at the time of precipitation as the quantum of rainfall has a bearing on the deposits.
Gypsum is a common mineral deposits that remain after the evaporation of saline water bodies and usually found at the cites of paleo-lakes.
If deposits in a particular layer is pure gypsum, it is an indication of scanty rainfall and predominance of evaporation during that phase of deposition.
This is because the surrounding areas in the region are all very sandy, and if there was rainfall, the rains-fed streams would have brought sand to the lake.
Contrarily, if there was considerable rainfall, the deposites would have a mixture of gypsum (evaporation precipitate) and sand (run-off deposit).
Similarly, pure sand can be an indication of very good rainfall as erosion and deposition is likely to have dominated over the miniscule gypsum deposits.
What were the specific conclusions?
These scientists have managed to establish a high resolution chronology of the wet and dry phases in the area between 9000 and 2000 BCE.
They have inferred that this region, northern part of Rajasthan, was largely dry till about 9000 BCE, which is 11,000 years ago from the present.
But between 9000 and 3000 BCE, there was substantial precipitation in the area, making it conducive for human settlements.
Further, monsoon is said to have intensified between 3000 and 2400 BCE, at the end of which a dry spell set in (which is continuing even today).
This showed that the peak of the civilisation almost coincided with the wet phase when monsoon intensified for about 600 years about 5000 years ago.
As the dispersal of the civilisation also coincides with the onset of the dry phase, this strengthens the climatic theory for its rise and fall of IVC.
The study has implications for modern society as well, as we are witnessing climate change and perceptible variations in precipitation and temperature.
