The Indus Valley civilisation’s mysterious collapse may have been driven by climate change

New research suggests that the disappearance of the Indus Valley civilisation was not the result of a sudden catastrophe, but rather of long-term processes. Scientists now increasingly believe that climate change may have played a decisive role in the decline of this once-flourishing civilisation of the Far East.

The Indus Valley civilisation – also known as the Harappan culture – was one of the most advanced civilisations of early human history, flourishing some five thousand years ago in what is now Pakistan and India.

Owing to its vast cities, advanced water-management systems, unique script and complex economy, it is often mentioned alongside the ancient empires of Egypt and Mesopotamia. Yet around 3,900 years ago the society began to decline, and within a few centuries it had vanished altogether.

Researchers have long debated which natural or social factors might have led to the civilisation’s collapse, but it now appears that they may be closer to a surprising answer: climate change, and in particular prolonged periods of drought, may have played a decisive role in the disintegration of this ancient society, writes Smithsonian Magazine.

The Indus Valley civilisation was struck by prolonged droughts

A recent study reveals that the region went through four extremely severe drought periods between 4,400 and 3,400 years ago. During this time rainfall decreased by 10–20 per cent, while average temperatures rose significantly.

The long-term and gradual effects of these changes are likely to have seriously affected agriculture and water supplies – both being fundamental to the survival of urban civilisations of the time.

According to the lead author of the research, Hiren Solanki, the Harappan civilisation was not brought down by a single catastrophic event, but rather by centuries of recurring fluvial droughts that gradually weakened the functioning of society.

Weather patterns in the region changed

The researchers compared meteorological data, palaeoclimatic samples and geochemical analyses with archaeological evidence. They found that between 3000 and 2475 BC, the region received abundant rainfall due to a cooler phase in the Pacific Ocean, but over the following centuries, ocean warming caused the monsoon system to transform completely.

Each of the droughts occurring between 2425 and 1400 BC lasted for more than eighty-five years, and at least one period affected the area for around 164 years.

As water sources dwindled, soils dried out, agriculture collapsed, and the population began a slow yet continuous migration towards more habitable regions. Harappan cities gradually broke apart, and the civilisation eventually fragmented entirely.

Remarkably, however, this climate stress was a very lengthy process – and according to geoscientist Liviu Giosan, it is striking that the civilisation managed to survive for centuries despite repeated crises.

Could we meet a similar fate?

The story of the Indus Valley civilisation is particularly instructive because humanity today faces a similar threat. The consequences of modern climate change are already affecting agriculture, water resources and human settlements.

According to palaeoclimatologist Sebastian Breitenbach, the past serves as a warning: if we are not prepared, long-term environmental changes are capable of bringing even the most advanced societies to their knees.

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