Are mortality figures for disasters fueled by climate change being underreported?

That question gained new relevance yesterday as research published in the New England Journal of Medicine indicated that 4,645 people died as a result of 2017’s Hurricane Maria.

That’s 72 times more fatalities than were officially reported by the government after Maria swept across Puerto Rico last Sept. 20, flattening homes; wiping out electrical service; and displacing tens of thousands of U.S. residents who had limited access to food, water and other basic necessities.

Yet in spite of the immense scale of the disaster, official government estimates placed Maria’s mortality figure at just 64 individuals as of late 2017.

That figure, according to researchers from Harvard University’s T.H. Chan School of Public Health and Beth Israel Deaconess Medical Center, is “a substantial underestimate of the true burden of mortality after Hurricane Maria.”

If findings are accurate, Maria would be the second-deadliest U.S. hurricane in modern U.S. history, following the 1900 Galveston, Texas, storm that killed an estimated 8,000 people.

The Lake Okeechobee, Fla., hurricane of 1928 was blamed for 2,500 deaths, while 2005’s Hurricane Katrina contributed to 1,800 mortalities mostly in Louisiana and Mississippi, according to National Weather Service data.

The Harvard research did not rely on formal reviews of death records or other documents submitted to Puerto Rican authorities. Rather, scholars surveyed 3,299 randomly chosen households across Puerto Rico to produce an independent estimate of all causes of mortality in the months after the hurricane.

“Respondents were asked about displacement, infrastructure loss, and causes of death,” the authors said. Excess deaths were then calculated by comparing post-Maria deaths with the official mortality rate for the same period during the previous year.

Analysis of the survey data showed a mortality rate of 14.3 deaths per 1,000 people from the period of Sept. 20 to Dec. 31, 2017, yielding a total number of excess deaths at 4,645 people with a confidence interval of 95 percent.

According to survey findings, interruption of medical care was the primary cause of sustained high mortality rates in the months after Maria, a phenomenon also observed after Hurricanes Katrina, Harvey and Irma, as well as Superstorm Sandy in 2012.

Moreover, the researchers said, actual mortality could still be underreported due to “survivor bias,” adding that one-third of the reported deaths were attributed to delayed or interrupted health care and that “hurricane-related migration was substantial.”

Independent experts say such findings speak to a broader concern among public health practitioners that damages from major weather events, including hurricanes, droughts and floods, are often underreported.

Kristie Ebi, an endowed professor of public health sciences at the University of Washington who has studied the health implications of climate change for 20 years, said in a telephone interview that tallying deaths from natural disasters has always been fraught with uncertainty, but study methods like those used by Harvard are the best way to overcome those limitations.

“These humanitarian crises are inherently chaotic, and to try to reconstruct the chain of causality of death afterward is quite difficult,” she said. “But it’s important that you arrive at a number that gives you a sense of the magnitude of the event.”

Ebi also said she was confident the researchers had arrived at a mortality estimate much closer to what Puerto Rico actually experienced during Maria. The government should use the findings, she said, to improve its own data collection methods so that disaster response policies can be tailored to meet the challenges of severe events.

The Harvard study notes that under Centers for Disease Control and Prevention standards, deaths from an event like Maria “can be directly attributed to a tropical cyclone if they are caused by forces related to the event, such as flying debris, or if they are caused by unsafe or unhealthy conditions resulting in injury, illness, or loss of necessary medical services.”

But while direct causes of death are relatively easy to assign by medical examiners and forensics experts, mortality resulting from indirect complications and conditions, such as chronic or worsening disease or delayed medical treatments, may not be fully recorded.

“These difficulties pose substantial challenges for the accurate and timely estimation of official all-cause hurricane-related mortality,” the researchers said.

Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at