Systems management offers another affordable approach. Instead of large civil-works projects to blunt the impact of climate change, places such as Seattle are modeling, adjusting and becoming more flexible to operating their stormwater and wastewater systems to a variety of climate scenarios.

Seattle has managed to avoid major climate adaptation investments by this portfolio approach, which may require operational, regulatory, policy or behavioral changes. "We're managing our reservoirs more dynamically," says Paul Fleming, Seattle Public Utilities manager of climate and sustainability.

Seattle is letting its reservoirs refill to higher levels than previously allowed and letting them go lower in order to maintain its water resources. Those seemingly simple management practices, however, can be complex in practice. For example, the Corps is experimenting with more-flexible management of water resources to adapt to climate change, says Goran.

"The Corps has a particularly tough situation," he says. "Drought affects navigation, but one management practice conflicts with another. If you release from reservoirs to improve navigation, it affects aquatic habitat and recreation."

But there are limits to managing systems and assets, which typically become obvious in extreme weather events or where rising sea levels are expected to be the worst: along the Gulf Coast or in the Northeast.

That's when climate adaptation becomes "difficult and expensive," says Black & Veatch's Wallis-Lage. Some climate adaptation will require expensive public-works projects, such as floodwalls or floodgates. In other instances, infrastructure will be abandoned and rebuilt farther inland or rebuilt at a higher elevation.

The Corps has been consulting with the military about which bases will need to adapt. Some would be affected by sea-level rise, but they also might be in an dought-prone area that could place troops under a higher stress level, Goran says. Currently, the Navy is determining how to manage climate risk at its Norfolk, Va., shipyard, which is at risk from sea-level rise and increased storm surge. The shipyard is a valuable asset, but the Navy may be forced to build a new pier on top of the old one or simply relocate.

NASA is contemplating similarly difficult choices at Cape Canaveral, Goran says.

Big decisions require long lead times. "It's going to take time or more events like Sandy" to push decision-makers into making the right choices, Neumann says. Right now, many view adaptation as pricey and unaffordable in an era of budget-crunching.

Deciding not to act has a price, says Gerry Galloway. "You're going to end up paying that money [to repair], and you're probably going to pay more. There are no regrets. You don't lose anything by acting."