The collapse of Angkor holds a lesson for today’s cities

A true wonder of the medieval world, the city of Angkor in what was once the Khmer Empire in today’s Cambodia is justifiably famed for its stunning temples and monuments. Constructed around an area of 1,000 square kilometers over hundreds of years, the world’s then largest city was home to a million people. Its sophisticated system of canals, water catchments and embankments made Angkor a feat of engineering.

But then, in the early 15th century, the magnificent civilization of Angkor collapsed. The cause was climate change. Intense monsoon downpours in the wake of prolonged droughts overwhelmed the city’s infrastructure to a point where it could no longer withstand the climatic battering. Within a relatively short period of time the city became uninhabited as the neighboring jungle proceeded to reclaim its streets and monuments.

According to a newly published study by an international team of experts, the collapse of Angkor’s famed civilization presents a warning to today’s major urban centers as the effects of climate change are bound to intensify in coming decades. “Complex infrastructural networks provide critical services to cities but can be vulnerable to external stressors, including climatic variability,” says Prof. Mikhail Prokopenko, director of the Complex Systems Research Group at the University of Sidney. “The cascading failure of critical infrastructure in Angkor which resulted from climate extremes re-emphasises the importance of building resilience into modern networks.”

Historians have long known that a major cause of Angkor’s fall was a changing local climate. Yet this new piece of research by scholars from various disciplines has shown that the medieval city’s infrastructure had systemic vulnerabilities to extreme weather events like prolonged torrential downpours. As the city continued to grow in size with more and more people living in it, its vital water networks became largely unmanageable.

“The water management infrastructure of Angkor has been developed over centuries, becoming very large, tightly interconnected, and dependent on older and ageing components,” Prokopenko explains. “The change in the middle of the 14th Century C.E., from prolonged drought to particularly wet years, put too much stress on this complex network, making the water distribution unstable.”

Numerous modern urban areas are facing similar challenges of overpopulation and complex infrastructure that makes them vulnerable to extreme weather events, the researchers note. These events can trigger a cascade of failures in complex systems, causing a city to became essentially uninhabitable for large numbers of people. “We found that infrastructural networks in preindustrial urban environments in fact share very common topological and functional characteristics with modern complex networks,” Prokopenko says.

“Not only is it possible that catastrophic, infrastructural failure may also have occurred in the past, but the results from this research are critical to our community’s understanding of how climate and distributed resources affect the functioning of our cities and societies,” the expert observes. “If we don’t build resilience into our critical infrastructure, we may face severe and lasting disruptions to our civil systems, [which] can be intensified by external shocks and threaten our environment and economy.”