Survival lessons from an ancient failed city

The city of Angkor Wat, Cambodia, was a vibrant, growing metropolis in the late 17th century. Angkor was the New York, Paris or Rome of its time. At its peak from the 9th to 17th centuries AD, no one could have imagined any threat to this Khmer city-state. Yet, Angkor collapsed almost totally in the 17th century, and the reasons behind its demise offer an important lesson for today’s cities.

Angkor was built on a vast transportation network: canals acted substantially like freeways. The metropolis grew by expanding its network of canals from the central city to form a vast complex of suburban satellites. As depicted below, this was a gigantic enterprise. Ankgor grew exponentially as internal wealth and power increased. The waterways allowed goods and people to move well beyond the central core of the city.

But as Angkor continued to grow, its waterways became more fragile and vulnerable. Rain and other small but severe weather changes occurred, and the system began to crumble. My colleague Roland Fletcher, a professor of architecture at the University of Sydney in Australia, describes this process as “low density metropolitan collapse.”

City expansion increases with wealth, which leads to suburbanisation.

Fletcher excavates cities to discover their social, physical, and economic trajectories. He and his colleagues have found a high correlation between extensive low-density suburbanization and subsequent metropolitan collapse. His thesis is that city expansion increases with wealth, which leads to, in essence, suburbanization.

Angkor expanded in a mild weather period. So, Angkor policymakers assumed this weather regime would continue forever and thus built their canals with few water catchments and earthen dams.

Today’s sprawling cities expanded in a period of mild weather too, with no anticipation that seas might rise or energy resources could be depleted. Angkor and modern cities resemble one another in that they were built to survive in only the most benign weather regimes. The roads, sewers and the like of the modern suburb are based on an assumption of mild weather and cheap energy. Recent events like Hurricane Katrina in New Orleans and subsequent Midwestern intense storms show how poorly modern infrastructure performs in extreme weather.

Elongated shallow roads and related infrastructure are as vulnerable today to destructive forces as Angkor Wat's canals were. Fletcher explains the consequences of this process from dense city to decaying suburbs.

There may be some debate over the causes and consequences of how cities rise and fall, but there is no doubt we have similar processes at work now in America. New Orleans, Grand Forks, North Dakota, and urban South Central Florida have experienced crippling disasters in the last two decades, where part of the cities have been destroyed beyond our capacity to rebuild them.

In 2012, there were more national emergencies for tornadoes, hurricanes, and snow storms that in any other year since records have been kept. As sea levels rise and weather patterns are increasingly unpredictable, basic city settlement systems are failing. Angkor Wat was not the first or last place to go through this evolution of city boom, sprawl and bust. Beirut and other cities around the world have grown and retreated as climatic conditions changed.

And of course, we don’t have to look as far back for even more analogues. As our energy supplies dwindle, we’ve watched as radical weather imperils America’s aging infrastructure. It is too simple to suggest that we can draw direct parallels here. But it is useful to learn from the past as we try to build or rebuild for the future. It is also unwise to suggest all suburbs are bad. What policymakers have to confront is what can we do in light of this past evidence.

Climate change plays a part but is not the sole culprit. New Orleans, where I spent considerable time post-Katrina as Recovery Czar, is a classic example of city sprawl. The city had almost 15,000 vacant units of housing in its core when the storm hit in 2005. City leaders had expanded the city into surrounding swamplands from 1965 to 1990, doubling the geographic size of the city. So when the storm hit, the city was expanded beyond the bulwarks of levees, leaving the entire city vulnerable to sea surges destroying much of the suburban infrastructure.

Cities can generate suburbs; but suburbs cannot save the city.

Many American cities have large suburban extensions held together by vast, over-stretched infrastructure. As Fletcher notes, the expansion of low-rise land use patterns require continued expansion of roads, water, and energy resources. This, in turn, could lead to a situation much like New Orleans, where the entire city framework is threatened when climate change alters rain, heat, and sea levels. Beijing experienced this phenomena last month with more than 30 lives lost because the expanded city could not support the volumes of flood water created by expansions of the city into surrounding natural habitat.

The lesson for American and similar land use pattern nations like Canada and Australia is to build compact, flexible settlements. One direction already underway is urban consolidation, in cities such as Miami, Indianapolis, and Louisville. Another is containment of sprawl, similar to Portland and Seattle and now Los Angeles.

Finally, Denver, Phoenix, and Dallas are trying to re-knit the suburbs with the cities using light rail to generate development along corridors rather than continuous outward development. All of these approaches at this point have merit, but they may not be enough to prevent massive systems failures. So as the nation debates the need for more infrastructure spending, it would be wiser to think of a strategy to improve city cores and reinforce transport spines. Angkor Wat is a useful lesson because it shows that if we don’t take drastic action, we are all facing the grim prospect of massive regional system failures.

Cities can generate suburbs; but suburbs cannot save the city.