Residences and major roads might be built to avoid inundation from a 1:100 year flood, while minor roads and recreational facilities might only be secured from a 1:10 year flood. Surprisingly, New York City is protected to only a l-in-100-year flood event, despite having a larger GDP than London, Shanghai, or Amsterdam, all of which are protected to a greater than 1-in-l 000-year flood (Amsterdam is protected from a l-in-10 000-year floods) (Nicholls et al., Australian red gum floodplain forests on the Murray River, for example, require flooding for one month or more in 70% of years, while drier floodplain woodland ecosystems only require flooding for two months or more in 25% of years. Each use of water thus has a different level of acceptable risk (in this case a risk of shortage for the ecosystems that require periodic flooding).