On Oct. 10, Yanira Rios collects spring water for use in her house, which is without running water or electricity after Hurricane Maria hit Puerto Rico. (Photo by Mario Tama/Getty Images)

Donald Trump tweeted on Thursday, “We cannot keep FEMA, the Military & the First Responders, who have been amazing (under the most difficult circumstances) in P.R. forever!” — putting Puerto Rico on notice that federal relief workers may be recalled.

But the images of the physical devastation from Hurricanes Irma and Maria throughout the Caribbean — especially on the U.S. territory of Puerto Rico — make it clear that it will take a lot of time and money to rebuild the damaged infrastructure.

The effects of hurricanes and other natural disasters, though, go far beyond the immediate physical cleanup. The impact on local health and demographics will likely have far-reaching consequences even after the power lines are back up.

Natural disasters are bad for population health

This year’s hurricanes have already affected these islanders’ health. Sanitation systems throughout the Caribbean were severely crippled; in Puerto Rico, Maria’s “apocalyptic devastation” left more than half of residents without access to clean drinking water.

Damaged infrastructure isolates communities and leaves hospitals without supplies, restricting access to health services. With the electrical grid essentially wiped out in Puerto Rico, many hospitals have to run on generators, if they can open at all. Without effective health services, responding to accidents and injuries from the hurricanes is obviously far more difficult.

The devastation of health care services also makes treating chronic conditions like diabetes far more difficult. In the aftermath of a natural disaster, these conditions see increasing death rates as access to medicines and medical supplies declines.

Officials in Puerto Rico are already raising the alarm about potential drug shortages. Ironically, Puerto Rico manufactures 25 percent of all U.S.-made pharmaceuticals — so production interruptions could have larger ripple effects.

Disasters can also bring new health challenges

Natural disasters like hurricanes also create new health concerns. Three conditions put a population at greatest risk from communicable diseases: overcrowding, poor sanitation, and lack of health care.

These are exactly the conditions we are seeing in the Caribbean after the recent storms. Because so many of Puerto Rico’s residents still lack running water, people on the island are bathing and washing clothes in rivers that may be contaminated with sewage, for instance.

Standing water after widespread flooding also creates ideal breeding grounds for mosquitoes, which makes malaria, dengue, chikungunya, and Zika bigger threats — especially as rain continues to fall. We have already seen how the introduction of diseases like Zika into new regions can have dramatic effects in both the immediate and the longer term.

The Centers for Disease Control (CDC) for now doesn’t expect to see cases of cholera in Puerto Rico, but other communicable diseases are likely, including hepatitis A, diarrheal diseases like giardia, and those mosquito-borne diseases.

And when health services are overwhelmed, even relatively treatable conditions can quickly become fatal. We have seen this before. During the 2014-2016 Ebola epidemic in West Africa, maternal mortality rates soared as health clinics had to devote all of their attention to Ebola patients and health care workers themselves fell ill and died.

The effects aren’t short-lived; they shape populations for years

Puerto Rico saw remarkable population changes before the hurricanes hit. The combination of low birthrates and high emigration meant that the island’s population was already shrinking. The hurricanes’ effects could exacerbate these changes — but previous research does not always give clear clues on the exact nature of these changes.

Here’s what we do know — in addition to changes in mortality and morbidity, populations also change from fertility and migration. In poorer regions around the world, fertility spikes occur after a disaster, because people are unable to access contraception. Fertility can also sometimes spike because of intentional decisions, when children can serve as an extra set of hands to earn income for the family.

In more developed regions, where children are not seen as laborers, disasters may actually depress fertility as couples put off having children. After Hurricane Katrina, displacement caused a 30 percent decline in birth cohort size. The post-disaster racial composition of New Orleans has shifted as black fertility fell and white fertility increased.

And in the medium term, fertility levels seem to normalize pretty quickly. In their study of the effects of Hurricane Mitch on Nicaragua, researchers found fertility did indeed spike in the wake of the 1998 disaster, but returned to normal levels four to six years later.

Puerto Rico’s high poverty rate could mean a short-term upward trend in fertility, as in Nicaragua, but that’s less likely, given how low fertility was in Puerto Rico before the disaster. The average number of children born per woman in the territory is far below the mainland United States, at only 1.2 compared to 1.9 for the U.S. overall fertility rate. A more likely scenario is that fertility will be further depressed in Puerto Rico.

Natural disasters also induce people to leave

While it is hard to isolate a single cause for migration, most research has shown that extreme weather events may displace people in the short term, though there are more mixed effects in the long term. After the devastating April 2015 earthquake in Nepal, there was significant internal migration, but some Nepalese returned from overseas to check on loved ones affected in Nepal while others stayed overseas to provide remittances as a steady source of income. Some research on Bangladesh has shown little relationship between flooding and permanent emigration, while research on longer-term environmental change, such as from climate change, and migration shows a positive relationship in Bangladesh and elsewhere.

There are already more Puerto Ricans in the mainland United States than on the island itself, and more than one-third of these Puerto Ricans settled in Florida. Puerto Rico’s bankruptcy, which may affect pension and health benefits as well as health and education services, is likely to be a driver of future emigration, though the disaster certainly will play a role.

On the aggregate, fertility, mortality and migration patterns will be most affected by the speed of the economic recovery in the affected areas. These changes could have important and long-lasting political, economic and social impacts — not just for Puerto Rico and areas hit by the hurricanes, but for the United States as a whole.

Jennifer Sciubba is a political demographer and associate professor of international studies at Rhodes College. Follow her on Twitter @profsciubba.

Jeremy Youde researches global health politics and is a senior lecturer in international relations at the Australian National University. Follow him on Twitter @jeremyyoude.