They may be richer and more numerous than ever, but the world's urban dwellers can be forgiven a sense of dread as threats pile up from climate change, terrorism and anarchic growth.

The fragility of fast-growing cityscapes has been exercising political and business leaders at the World Economic Forum in Davos this week.

One projection from the Brazilian consultancy Igarape said cities will account for two-thirds of the world's population by 2030, from just over half now. The bulk of that growth will come from just three countries: China, India and Nigeria.

Already the motors of the world economy, some "super-cities" will increasingly resemble nation states with power and influence to go with their teeming populations.

But a major theme of the Davos meeting was how they must show "resilience" with proper urban planning.

Inside the forum's main congress hall, a data visualisation by Igarape was projected onto a big screen to rank cities: the higher the number, the more vulnerable they are to the totality of risks under discussion.

Paris, with a fragility ranking of 2.18, came in worse than Dakar in Senegal (1.33) but Baghdad was still worse on 3.88.

"The world is becoming increasingly urban," noted Igarape's Canadian research director, Robert Muggah, "and their (cities') resilience, success or failure, will shape how a lot of our nation states perform globally".

The concept of urban resilience requires authorities to appreciate the scale of the problem and take remedial steps, French geographer Magali Reghezza said.

"Even if we can't eliminate the risks, even if we can't entirely avoid crises, we can stop them turning into disasters. And even if there is a disaster, relief is possible," she said.

The recent past in Paris and Brussels has shown the stark threat of mass urban terrorism. But longer term trends are also building, with some coastal cities menaced by rising seas.

Others suffer the self-inflicted harm of uncontrolled growth as slums proliferate without the infrastructure -- in terms of basic sanitation and roads -- needed to make the growth sustainable.

Criminality and social tensions accompany such a free-for-all, depriving governments in the developing world of the stability needed to plan for the long-term and ensure their cities can power the national economy rather than drain it.

"Three challenges are manifest across the urban world: natural risks, in particular hydro-climatic ones, technological blackouts, and mass terrorism," Reghezza said.

Paris mayor Anne Hidalgo said she had appointed a "chief resilience officer" to ensure the French capital is facing up to its own long-term challenges such as flooding and security.

"We're very committed on this issue," she told AFP, noting that Paris last year hosted a global summit grouping city authorities to debate common solutions.

Some 50 other cities have also appointed resilience officers, according to the Rockefeller Foundation, which has launched an initiative called "100 resilient cities" and is advising city mayors.

The sort of future-proof planning involved doesn't come cheap.

The global need for urban infrastructure investment -- such as developing transport, flooding control and utilities -- amounts to more than $4.5 trillion per year, according to the World Bank.

A significant mark-up over that figure is necessary if authorities want to make their infrastructure low-emission and resistant to climate change, it added.

Insurers are already seeing the rising costs when preventive action is not taken.

Natural disasters around the world caused a record $175 billion in damage last year, the German reinsurer Munich Re said.

But taxpayers in cities that can show adequate resilience planning can expect to shell out less in premiums.

The services group Veolia last year signed a partnership with Swiss Re, with support from the Rockefeller Foundation, to offer technical advice to cities.

"It's an issue that's only going to take on importance," Veolia chief executive Antoine Frerot said. (AFP)