Benedicta Reyes stood on a riverbank in Huachipa, a neighborhood on the east side of Peru’s capital city, looking at what was left of her house. On the afternoon of March 13, a flash flood of roiling, mud-brown water had swept away two trucks and carved away the bank.

By the next morning, parts of her home and several others had collapsed into the water, leaving ragged walls perched at the edge of a crumbling precipice.

Five days later, Reyes, 73, stood in line with her neighbors to fill buckets with water from a tank truck. There was no telling when electricity or water service would be restored to her neighborhood, or whether she would be able to rebuild her home.

Reyes is one of more than 125,000 people who have lost their homes since then in what has been a growing disaster.

A mass of unusually warm water along Peru’s northern coast has caused heavy rains to pummel normally arid cities, triggering floods and landslides that have killed at least 97 people, injured at least 350, and left nearly 813,000 with property damage.

On the north coast, waist-deep water filled Piura’s main square, and Chiclayo and Trujillo are also awash. Elsewhere, landslides have sporadically closed many mountain roads, including the key Central Highway that connects Lima, the capital city of 10 million people, with the Andean highlands and Peru’s central Amazonian region, which are key food-producing areas. The slides have cut hundreds of people off from roadways and essential services.

The images of rescues from swollen rivers and houses collapsing into floodwaters underscore the lack of urban planning and enforcement of zoning regulations in most Peruvian cities. Yet the rain that has wrought disaster for humans also is a boon to plants and animals on the arid coast, sprouting seeds that have lain dormant for two decades and making dry lands fertile again.

The “coastal El Niño,” as Peruvian meteorologists and climatologists have dubbed it, caught experts off guard. It was not due to the classic El Niño pattern—an influx of warm ocean water from the central Pacific as was the case in two of the strongest El Niños on record, in 1982-83 and 1997-98, and in the El Niño that affected the northern hemisphere in 2015 and 2016. (See “For this El Niño, region was better prepared”—EcoAméricas, Jan. 2016.)

Instead, the current conditions occurred when coastal winds from the south subsided and winds from the north brought warmer water south from Ecuador, according to Dimitri Gutiérrez of Peru’s Institute of the Sea (Imarpe), who heads a multi-agency committee for the study of the El Niño phenomenon.

Gutiérrez says that the heavy rains caused by moisture rising from the warm water will likely taper off in April, although some forecasts have the severe weather lasting until June.

Damage estimates exceed US$3 billion, and government officials say the disaster could shave a percentage point off the country’s economic growth this year.

Northern cities were cut off from Lima when a key bridge on the coastal Pan-American Highway collapsed. Some 9,300 kilometers (5,800 miles) of highway have been destroyed so far and another 12,600 kilometers (7,800 miles) damaged, according to government reports.

Much of the flooding is similar to that of the strong El Niños of 1982-83 and 1997-98, but damage is greater because now more people are living on unstable slopes and in floodplains, says Gilberto Romero, president of the board of the nonprofit Center for Disaster Studies and Prevention (Predes) in Lima.

Of the 53 rivers on the western slope of the Andes Mountains in Peru, only a dozen flow year-round. Others may channel water between December and March, during the rainy season in the highlands, but some have been dry for decades.

On the northern coast, peripheral urban areas as well as the city centers of Piura, Trujillo and Chiclayo were flooded. In and around Lima, the disaster disproportionately affected people in low-income areas on the eastern edge of the city and rural mountain towns, although some middle-class eastern neighborhoods have also been struck.

Over the years, people have built houses on dry riverbeds or in steep ravines where flash floods occur with little warning. In places, entire neighborhoods have grown up in the path of potential mudslides, sometimes helped along by land speculators who mark off and sell lots on government land or in areas where land ownership is murky.

Many of the people who buy those lots will never be able to obtain title, finding themselves in limbo when disaster strikes.

A lack of attention to hazards combined with the tendency of families to build their own homes a room at a time, without architectural plans or compliance with building codes, adds to the danger.

“There’s not a habit of considering risk and taking steps to reduce it,” Romero says. “Cities expand when people who need housing occupy vacant land. No one has managed to change that.”

Flooding is not the only risk to precariously built houses. Some hazard assessments estimate that a severe earthquake in Lima would leave half a million homes uninhabitable and kill as many as 60,000 people.

Peruvian President Pedro Pablo Kuczynski has pledged that reconstruction will take hazards into account, but many local governments lack funds and personnel with urban planning experience, Romero says.

One of the areas hardest hit by landslides was in the foothills of the Andes east of Lima, where the Central Highway follows the course of the Rimac River.
Mud, rocks, trash and debris from more than a dozen landslides swept into the Rimac and overwhelmed the water treatment plant that serves most of Lima, forcing the state-run water company to shut down the system for several days.

News photos showed water company workers fishing debris and dead animals from a grate at the plant’s intake, but company representatives said the shutdown occurred because high concentrations of sediment from landslides overwhelmed the plant’s filtering capacity. When the plant stopped sucking water from the Rimac, the downstream flow swelled, shredding the riverbank and causing a bridge to collapse.

The landslides and flooding highlight the twin problems of lack of prevention and poor engineering, says Jorge Abad, director of the environmental engineering program at the University of Engineering and Technology (UTEC) in Lima. Although this year’s rainfall and flooding mirror those of 1997-98, “in 20 years nothing has been done” to prevent another disaster, Abad says.

The Rimac River overflowed its banks in downtown Lima where it has been channeled and narrowed for development projects. And the lower part of the Piura River basin has been engineered for irrigation with no calculation of possible peak sediment flow from the upper watershed, he says.

“Prevention doesn’t mean dredging, widening the riverbed or building more barriers,” Abad says.

Instead, reconstruction must be based on scientific studies and modeling of the rivers and their sediments to project the impacts of the El Niño-style rain, combined with regulations to keep humans from settling in high-risk areas.

While families in lower-income neighborhoods on the east side of the city cleaned mud out of their houses or wondered how they would rebuild, residents of upscale neighborhoods far from the disaster area snapped up bottled water, forcing supermarkets to set per-customer limits.

The clouds giving cities a drenching do have a silver lining for the coastal dry forest, which has seen very little moisture since the 1997-98 El Niño.

“El Niño is a biological explosion—it’s a great biological experiment,” says biologist Juan Torres of Lima’s La Molina National Agrarian University, whose research centers on the north coast.

Seeds of plants like the carob tree or algarrobo (Prosopis spp.), which have lain dormant in the sandy soil for decades, are sprouting, along with wild relatives of such domesticated crops as tomatoes, peppers, potatoes and squash.

Although flooding has destroyed or damaged 48,000 hectares (120,000 acres) of cropland, according to government reports, the rains have made some desert areas arable again.

The farming community of Belisario in Piura is normally home to about 30 families, but the number has tripled as people who had migrated to other areas return to take advantage of the growing conditions, Torres says.

He is waiting for roads to become passable to see what wild plants have sprouted with this year’s rain and what unusual seeds the farmers are sowing. After the 1997-98 El Niño, some farmers in Piura planted varieties of crops, including cotton, that he had never seen before.

The effects of rain in Peru’s northern Sechura Desert are likely to last for several years. A huge lagoon has formed in the Piura region, covering a larger area than a similar lake that resulted from the 1997-98 El Niño.

But the drenching that is turning the desert green also has ecological downsides. Insect pests multiply after El Niño rains, Torres says. Piura is already one of Peru’s hotspots for dengue, a mosquito-borne illness, and cases of leptospirosis, a disease carried by rodents, have been reported on the coast. Banks of abalone in coastal waters have died, Gutiérrez says, either because they were covered with sediment or because they could not tolerate higher seawater temperatures.

On land, the rain is likely to cause invasive tamarisk trees, probably introduced to Peru in the first half of the last century, to spread further. Tamarisk (Tamarix spp.) began expanding in the north after the 1982-83 El Niño, crowding out native vegetation in the dry forest.

The tree, a destructive invasive in the western United States, absorbs large amounts of water and exudes salt, which could further deteriorate soil in desert areas where salinity is already a problem.

While this year’s coastal El Niño offers research opportunities for biologists, it also poses some puzzles for climatologists.

El Niño events appear in paleoclimate records over the past 20,000 years, and some archaeologists believe that extreme weather linked to El Niño was responsible for the collapse of some cultures that rose and fell along Peru’s coast.

This year›s extreme weather is part of that cycle, rather than a consequence of global warming, although experts say climate change could increase the frequency or intensity of El Niños.

References to heavy rain in colonial records offer the only clues to El Niños in modern times. One of the earliest references mentions El Niño conditions in 1541, less than a decade after Spanish conquistador Francisco Pizarro arrived in what is now Peru.

Scientific data collection began just about a century ago, with a hiatus during World War II, says Ken Takahashi, principal researcher at the Geophysical Institute of Peru (IGP).

Records from the early 1900s indicate that the El Niño of 1925 was probably a coastal phenomenon similar to this year’s, Takahashi says. Nearly a century later, however, scientists still do not know how to predict such an event, because it depends on winds that can only be forecast a week or two in advance.

They know far more about the El Niño events that begin in the central or western Pacific Ocean because they are easier to forecast, building up as they do over months.

Even so, global climate models for the Peruvian coast tend to be inaccurate, Takahashi says, because while ocean temperatures off Peru fluctuate, those used for the models tend to be those at the high end of the range. “These errors affect forecasting of El Niño,” he says.

Takahashi, one of a group of young investigators who have done doctoral studies abroad and returned to work in government meteorological and climate research agencies, says more study is needed of climate patterns in the central Pacific Ocean and temperatures below the ocean surface.

But the greatest lack, he said, is not measurements, but people.

“We have data,” he says. “What we really need are researchers, because there are few in Peru, and there needs to be a government policy to promote that.”