George Santayana said “Those who cannot remember the past are condemned to repeat it.” As we live through another superheated Indian summer and see vast swathes of the country experience water scarcity, we found this piece by the historian Anirudh Kanisetti a timely reminder of how vast Asian empires have been laid low by the same issues which we are experiencing today. Mr Kanisetti says “Indians created fragile systems that collapsed under environmental pressure. The best example of this is the Indus Valley Civilisation. The history of Asian empires warns us: climate disasters wait for no one. The most populous city in the world was laid low by the monsoon; the most advanced Bronze Age civilisation was emptied by drying weather; and climate disasters played into the fall of both North Indian and South Indian empires.”

Mr Kanisetti first case study of climate change bringing down a powerful empire is from Angkor Wat, the (still) stunningly beautiful temple complex in Cambodia: “The largest Hindu temple in the world, Angkor Wat, is reflected in the waters of a man-made lake. Around it is a vast abandoned city: Angkor, Cambodia. In the 12th–13th centuries CE, Angkor was perhaps the largest city in the world—larger even than Indian cities at the time. Extending nearly 1,000 square kilometres, the region was home to as many as a million people. In comparison, the largest pre-modern Indian city, Vijayanagara, had perhaps 4,00,000 inhabitants.

To feed so many mouths, the people of Angkor built hydraulic works over the course of 300 years, gradually expanding and connecting smaller systems. The end result was a stupendous water collection and distribution network, extending over nearly 3,000 square kilometres. An extensive multidisciplinary study found that this consisted of three main zones. Rivers flowing from the Kulen mountains in the north were diverted in the first, uppermost zone. The middle zone aggregated this water in massive tanks in the city, with a total capacity of up to 1.2 billion litres. Many of these tanks surrounded temples or were adjacent to them. This enormous body of water was slowly released for rice cultivation, tiding the city through Cambodia’s long summers. Excess water was collected by a drainage zone and delivered to the Tonlé Sap Lake—the largest freshwater body in Southeast Asia.

But Angkor was hit by a series of climate disasters in the 14th century, seriously weakening its water systems. Part of the flaw lay in the system itself. It was not a single united plan, but a series of expansions and corrections to smaller plans—all with their own issues.

Hydrologist Matti Kummu writes that in the upper hydraulic zone, Angkor’s engineers built straight collection channels, breaking apart the catchment area of the Puok river, and cutting the water across the natural slope. Water flows much faster in straight channels, eroding the banks and depositing massive quantities of silt. But much bigger problems were two droughts that lasted for decades in the 14th century. Engineers were forced to make expensive modifications to the system. But then, right after the drought, torrential monsoons overloaded the fragile water system, destroying huge sections and forcing the city’s kings and masses to move elsewhere.”

Closer home, it seems that the great Chola rulers of the south also goofed up in the face of environmental disaster: “Environmental stress also played into the collapse of the Chola Empire in South India. As historian R Tirumalai writes in Land Grants and Agrarian Reactions in Chola and Pandya Times, from the 12th century onwards, there were repeated floods in the Kaveri and Cheyyar river systems. The floods were bad enough, but landlords disastrously mismanaged the crisis, insisting that cultivators pay tax anyway. Others used the crisis as an opportunity to buy land for cheap. This short-sighted speculation made many rich but left others destitute. By the late 12th and early 13th centuries, inscriptions reveal that people were selling themselves into slavery. The natural crisis was worsened by human action.”

In fact, Mr Kanisetti says that ecological stress was used by foreign invaders to dislodge one of the greatest Indian empires: “There are other tantalising examples. In The Fate of Rome: Climate, Disease and the End of an Empire, historian Kyle Harper studied ice cores and tree rings. It turns out that in 536 CE, volcanic eruptions led to catastrophic global cooling. Documents from all over the world describe a darkening of the skies, longer winters, and failing harvests. Around the same time in India, the Huns from Central Asia were pressing into the Gangetic Plains, leading to the collapse of the Gupta Empire.”

And just in case, in the midst of the ongoing election campaign, our policymakers haven’t clocked it, Mr Kanisetti ends his piece by saying “We can’t keep going the way we are and pretend everything will be fine. The least we can do is learn from the triumphs and struggles of our ancestors.”

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