The plans for the 2008 Beijing Olympics are notable for their extra security amid human-rights protests. But the 2012 London Olympics’ park plans are notable in that they consider a climate-changed future, in which flooding may worsen and cities must minimize carbon emissions.

London’s summer-games site straddles the polluted Lea River on the east end of the city, now a moribund industrial area dotted with depressed neighborhoods. The planners looked at climate models and recognized that the area, known as the Lower Lea Valley, would likely be carrying higher flood waters from intensifying rainstorms.

Jason Prior, president of the planning firm EDAW, explained one consequence of this finding at a conference on Friday: the planners ran hydrological models to determine how to widen the river and design new bridges to accommodate the higher flows. “You survey the river systems, then project forward the impact of different flow conditions, and you add the amounts the climate models are giving you,” Prior said after a forum on climate change and cities at the Lincoln Institute of Land Policy, in Cambridge, MA. “You then fine-tune the channel’s cross sections, change design of bridge abutments, and design wetlands to catch the extra amounts.” Site work has already begun.

Equally important in London’s climate-minded preparation is the post-Olympics plan for the region. Housing for 17,000 athletes will become housing for 4,000 families; plazas will become parklands. The plan includes highly efficient housing powered partly by a wind turbine and biomass plant, with pedestrian links across the river connecting to transit stations, and new amenities like schools and shops.

This idea–planning entire neighborhoods around energy efficiency and reduced emissions–is part of an emerging trend in which efficiency is thought of as something more than discrete buildings, houses, cars, and appliances. “Missing altogether from these ‘widgets’ is any notion of urbanism,” Douglas Farr, principal at Farr Associates, a Chicago-based planning firm that focuses on sustainable design, said at the conference. He added that planners need “urban parts”–meaning entire sustainable and efficient neighborhoods–that can be, in effect, plugged into a city or suburb.

To this end, Farr helped develop a new energy-efficiency standard called LEED-ND. This expands the existing LEED (Leadership in Energy and Environmental Design) rating system for individual buildings by adding the “ND” for neighborhood development. Features of high-efficiency neighborhoods include walkable shopping and services, bike paths, renewable district power generation, connections to mass transit, and shared car usage, perhaps assisted by location-based technologies to let residents know where and when vehicles are available.

Thinking about remaking a whole city in these ways can be daunting, Farr said. But breaking it down into such neighborhoods–early examples of which are under construction around the country–offers a means to assembling them into far larger regions, he noted. “I believe in promoting neighborhoods that are organized in corridors. Then a region becomes a collection of corridors.”

Bob Yaro, president of the Regional Plan Association, a civic group serving the New York metropolitan area, takes that idea a step farther: the association is hoping to galvanize support for emerging “megaregions” as much as 600 miles across in which several cities and their suburban regions are linked by affordable and frequent fast trains. “Much as cities were connected by interstate highways, megaregions will be organized by high-speed intercity rail,” Yaro said at the conference.

Meanwhile, his group, together with New York City’s government, is promoting green developments and transit enhancements within the city, part of a public-private effort that aims for a 30 percent reduction in local greenhouse-gas emissions. It is one of several such urban efforts under way around the country.

Of course, getting such visions realized won’t be easy. But cities, with their economic and voting mass, can get the job done, Yaro said. “Cities have got to lead in this effort. We need the impetus of global treaties and national policy. But in the end it will be the great cities, the Washingtons and New Yorks, that will achieve these climate goals.”