As the Northeast struggles with the aftermath of the massive storm Sandy, many experts say the government for years has underestimated how much of the nation is prone to flooding, given the increasing likelihood of extreme weather because of climate change and the prospect of future sea level rise.

These experts, who include not only environmentalists but also community planners, insurers and fiscal conservatives, have pressed agencies such as the Federal Emergency Management Agency to rethink the way the government evaluates the risk of floods. Such a change could affect where and how infrastructure is built and make it harder to develop vulnerable areas.

FEMA, which is updating flood insurance maps from the 1980s, is setting up a “technical mapping advisory council” that will study how the agency might take future climate change into account. At this point, it still bases its analysis on historical data.

But Sandy’s devastating punch might bolster the case for change, given how it exposed many areas’ vulnerabilities to storm surge and sea level rise.

New York Gov. Andrew Cuomo (D) said policymakers need to acknowledge that the infrastructure in place along the East Coast cannot withstand the changing climate.

“Anyone who thinks that there is not a dramatic change in weather patterns is denying reality,” Cuomo said at a news conference Tuesday. “We have a new reality, and old infrastructures and old systems.”

Flood planning is based on historical data rather than future projections. And much of the infrastructure damaged in a storm is rebuilt exactly the same way, without taking into account the climatic changes underway.

FEMA draws the flood maps to provide guidelines to local authorities who determine where things can be built. Many developers and homeowners have resisted the idea of expanding the definition of flood risk because it raises costs and can restrict development. Policymakers “are afraid of the political backlash,” said Georgetown Climate Center executive director Vicki Arroyo.

And expanding the maps means increasing the area covered by the 44-year-old National Flood Insurance Program, which covers Americans in flood-prone areas with federally backed insurance provided they meet federal standards aimed at minimizing risks. The program was at least $17.75 billion in debt before Sandy made landfall, and the storm could deplete the program’s remaining $3 billion statutory borrowing authority. The insurance is voluntary.

Proponents argue that the flood insurance program provides coverage that would otherwise be unaffordable and saves taxpayers money by prodding communities to take precautions. Critics say the program encourages Americans to build in vulnerable areas, with 40 percent of the total payout going to 2 percent of properties that were repeatedly flooded.

“Climate change is only happening in one direction,” said Kevin Trenberth, a senior scientist at the National Center for Atmospheric Research. “The temperature is warmer, the sea level is higher and the air is warmer so it can hold more moisture.”

Several recent studies indicate intense precipitation events are worsening, especially in the Northeast, partly because of climate change. A recent analysis by the U.S. Global Change Research Program found rainfall totals that were considered 1-in-100-year events in the 1950-78 period were 1-in-60-year events between 1978 and 2007. By 2100, according to the U.N. Intergovernmental Panel on Climate Change, rain events in the Northeast that are now 1-in-20-year events will take place every four to six years.

Twenty percent of properties that claimed at least two losses in 10 years under the federal insurance program between 1978 and 1995 were outside the areas FEMA had mapped as a high flood risk, according to flooding consultant David Conrad.

FEMA issued a memo on Jan. 23, as part of President Obama’s executive order requiring agencies to develop a climate-adaptation plan, saying it would take climate change into account in preparing for and responding to severe storms, droughts and heat waves. That document said FEMA would “continue to study the impact of climate change on the National Flood Insurance Program (NFIP) and incorporate climate change considerations in the NFIP reform effort,” as well as into the cost-benefit it conducts when investing in infrastructure.

But Senate Democrats did not consider the memo concrete enough. They inserted language into the highway bill that Obama signed during the summer directing FEMA to consider climate change when drawing up flood maps. Specifically, the law tells the agency to consider “any relevant information . . . relating to the best available science regarding future changes in sea levels, precipitation, and intensity of hurricanes.”

It is unclear how FEMA will implement these policies. The agency commissioned a study that concluded two years ago that the size of the nation’s flood plains could increase by 40 to 45 percent by the end of the century because of rising seas and more intense precipitation, but the agency has not released the analysis publicly. A FEMA spokesman said the study is “under review by federal agencies with expertise in climate sciences.”

“The key agencies charged with managing floods and disasters in this country have had their heads in the sand for many years when it comes to climate change,” said the National Wildlife Federation’s vice president for wildlife conservation, John Kostyack, whose group has sued FEMA and the Army Corps of Engineers for failing to take climate change into account when making policy decisions.

By contrast, the Federal Highway Administration issued a Sept. 24 memo saying federal dollars can be spent on adapting transportation infrastructure to climate change and extreme weather.

Officials in Vermont, which has experienced a flooding disaster every year for the past quarter-century and suffered widespread damage from Hurricane Irene in 2011, have sparred with FEMA on several fronts. The agency recently denied Townsend, Vt., the funds to build larger culverts to manage the level of flooding it recorded last year. FEMA also does not take into account the erosion Vermont is experiencing with more powerful storms, since it only considers inundation floods.

“We already know they are undersized, and we know they will be destroyed in the next flooding event,” said Deborah Markowitz, secretary of Vermont’s Agency of Natural Resources, referring to the culverts. Markowitz added that since the state requires communities to take the latest river science into account when rebuilding infrastructure, “That’s a major source of tension right now.”

Other facilities that have met federal guidelines have also been overwhelmed by extreme weather events: in March 2010 a water treatment plant in Warwick, R.I., that had been built to meet FEMA’s flooding requirements shut down after having no plan to cope with the extreme flooding it experienced.