different from current ones. Architects and engineers must therefore account for the future changes that can be expected. Table 1 below shows examples of sectors involving long-term planning, long-lived investments, irreversibility in choices, and exposure to changes in climate conditions.

|**_Table 1. Sectors with irreversibility, high inertia an_**<br>**Sector**|**_d high exposure_**<br>**Time scale**|**_to climate conditions_**<br>**Exposure**|
|---|---|---|
|Water infrastructure (e.g., dams, reservoirs)|30–200 yr|+ + +|
|Land-use planning (e.g., in flood plain or coastal areas)|>100 yr|+ + +|
|Coastline and flood defences (e.g., dikes, sea walls)|>50 yr|+ + +|
|Building and housing (e.g., insulation, windows)|30–150 yr|+ +|
|Transportation infrastructure (e.g., port, bridges)|30–200 yr|+|
|Urban planning (e.g., urban density, parks)|>100yr|+|
|Energy production (e.g., nuclear plant cooling system)|20–70 yr|+|

source: Hallegatte et al. 2012

**_In all these sectors, the choice of_** technology leads to path dependence. The clearest example of path dependence is that of the standard gauge for railways (4 feet 8-1/2 inches or 1.435 meters) throughout North America, Europe and half of the world's railway routes. Despite having more technically and economically optimal alternatives, the decision by British engineer George Stephenson to use this gauge during the 19<sup>th</sup> century ensured that this outdated technology is still in use today (see Puffert 2000 and 2002). Making decisions on these kinds of investments therefore require anticipating the long term environment, the demand for infrastructure and the constraints under which they will function. This need for anticipation brings large uncertainty into the decision-making process, for instance from demographic or economic projections. Past evidence suggests that our ability to predict the future is rather limited but that uncertainty has to be taken into account before decisions are made.

There are two ways to manage uncertainty. The first is for decision makers to use available decision-making methodologies, from simple heuristics (e.g., adding safety margins to all design characteristics to cope with larger-than-expected extreme events) to sophisticated methods (e.g., based on subjective probability and cost-benefit analysis). These techniques are described, for instance, in Hallegatte et al (2012). The second way to take the future into account and manage uncertainty is simply to use common sense, making sure that today's investment decisions do not lock cities out of options tomorrow so that they can adapt to unforeseen new circumstances.

Flexible vs. inflexible strategies can be illustrated by opposing China’s strategies in energy and transport. China has been very innovative when it comes to renewable energy. About 17 percent of China's electricity came from renewable sources in 2007, led by the world's largest number of hydroelectric generators.<sup>14</sup> Technology development and increased amounts of investment in renewable energy technologies and installations have increased markedly throughout the 2000s in China, and investment in renewables was part of China's economic stimulus strategy. China is one of the four largest producers of wind power (with the United States, Germany, and Spain)

> 14  By 2009, China had a total installed capacity of hydropower of 197 GW.

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