In December 2009, a late‑afternoon storm unleashed torrential rain over Ayacucho, in Peru, hitting poor hillside neighbourhoods hard. The deluge overwhelmed drainage systems, turning streams into lethal flows of mud, stones and debris that flooded houses and streets and trapped drivers at a busy junction.

Ten people died, 18 were injured, and 530 houses were destroyed or damaged, according to a government inquest. “It was a disaster,” recalls Edgar Castro, a leader in Ayacucho’s largest informal neighbourhood, Mollepata.

Nearly 17 years on from the tragedy, thousands more have built their houses in areas at high risk of extreme weather on the outskirts of Ayacucho. Castro, who lives with the threat of history repeating itself, represents 34 community groups who are working with local government to bring these areas – starting with Mollepata – into the fold of urban planning.

Throughout Latin America, one in five people live in unplanned settlements, built haphazardly and often in high-risk zones for flooding, landslides or drought. These are inherently more vulnerable to natural disasters brought on by the climate crisis.

“As extreme weather events become more frequent, the urban poor are simultaneously exposed to temperature extremes and least equipped to manage them,” says Cynthia Goytia, professor of urban economics at Torcuato Di Tella University in Buenos Aires.

Mollepata is a telling example in Latin America. Self-built adobe or brick houses with corrugated metal roofs balance precariously on steep slopes bordering the road from Ayacucho’s centre. What starts as a paved road soon turns into a dusty, pothole-ridden path.

Until the early 2000s, few people lived here. But as property prices soared, new arrivals occupied former grazing land on the city’s rural outskirts. This grew into Mollepata, where people crowd into informal dwellings, at about seven times the density of Ayacucho itself.

Between 2007 and 2017, Mollepata’s population increased 20-fold, from 316 to 6,624, according to Ayacucho authorities, who estimate that by 2027 it will reach 17,000. Yet, according to people who live there, official data bears little relation to reality. “Mollepata has more than 30,000 inhabitants if you count kids, adults and old people,” says Castro, adding that they live “in a no-man’s land”.

Two-thirds of its population and all of its schools are in areas deemed high-risk for natural disasters, according to authorities. And it is just one of several informal neighbourhoods whose rapid growth aggravates the already alarming risk of extreme weather disasters for those neighbourhoods and for Ayacucho as a whole.

Ayacucho lies in the heart of the Peruvian Andes, where annual rainfall has halved since 1984. The local glacial peak has also lost 95% of its snowcap. For city dwellers that means shorter, less predictable rainy seasons. Rainfall, when it comes, drops in short, increasingly intense storms that overtake the Ayacucho valley, causing floods and landslides.

The rest of the time, people face severe water shortages and soaring temperatures, made worse by concrete structures that trap heat. Poorly constructed dwellings in informal settlements are worse still, with inadequate ventilation and inefficient cooling systems.

This way of building turns whole neighbourhoods into “little ovens”, says Juan Carlos Prado, an environmental specialist working for the municipality.

The informal neighbourhoods at highest risk from these disasters also tend to be the most underserved. They lack reliable water systems and accessible emergency or medical services – so when a catastrophe hits, they are the least prepared to respond.

Many rely on just one unpaved access road – a single bridge connects Mollepata to the rest of Ayacucho. “If that collapses, they’re isolated in an instant,” Prado says.

With this in mind, and under the shadow of the 2009 tragedy, the municipality runs education campaigns. But Castro says that many people “still don’t take these consequences into account”.

According to experts, the only solution for those in risky terrain is to move. “We can’t negotiate with nature. We can’t get in the way of the rivers,” Prado says, though he doesn’t know a single case in which people voluntarily abandoned their plots.

“Families make calculated trade-offs between affordability, proximity to livelihoods, and existing social networks, often accepting elevated environmental risk as the price of urban access,” says Goytia.

The city has no money for relocation programmes, according to Prado. “They say to us, ‘Where can I go?’ ‘Where do you want me to live?’ ‘Solve it for me’,” he says. “But what solutions can we give? The only thing we can say is, ‘Try to find another place because you are too exposed’.”

In 2025, Ayacucho municipal government published a plan to improve public services, structure private and public land, and establish measures to manage disaster risks. Since then, it has begun meeting association leaders to bridge the gap between plans drawn up in municipal offices and the reality on the ground.

The climate crisis is making the environment more arid and the dirt road more dusty, damaging people’s health and quality of life. By grading and compacting the main road, officials hope to minimise dust and make it easier to get to Ayacucho, where most emergency services are concentrated. Drainage ditches will be built to mitigate the risk of flash floods from the rainy season.

Yet, bringing in government retroactively comes with challenges. Because of existing irregular water infrastructure under the road, the drainage ditches must be shallow. And while the government will provide machinery, local people must remove any debris and guide the machines, as only they know where underground tubes run.

Mollepata’s community leaders seem more than ready to meet these demands, promising to rent a dump truck and coordinate volunteer groups. They also discuss the need to increase green areas, vital to mitigating the urban heat-island effect.

The town official in charge of reforestation promises to provide people with tree seedlings in the rainy season, when water is less scarce. There is even land set aside for a park.

“Over the past four decades, Latin American governments have largely moved away from demolition and forced eviction toward formalisation, regularisation and comprehensive neighbourhood upgrading programmes,” Goytia says.

But the efforts in Mollepata demonstrate how challenging this policy shift can be, given local governments’ resource constraints. Integrating Mollepata into the city will cost more than 530m soles (about £116m), almost five times Ayacucho’s municipal annual budget, according to official estimates. A shorter list of high-priority projects would still cost 460m soles.

For local people, issues such as insecurity, lack of transport, and rubbish disposal are often more urgent than water shortages, floods and avalanches. While authorities and those established in Mollepata work to integrate it into the city, new settlements are emerging as rural Peruvians seek footholds there.

With most of the relatively safe areas already built up, recent years have seen a sharp increase in building on steep slopes, in ravines and along riverbanks. “The situation is becoming critical,” Prado says.

Still, at least in Mollepata, local people and municipal workers strike a hopeful tone. Castro sees the approval of his settlement plan as a great achievement and lauds officials for travelling to the settlement to meet the people.

“By getting their boots dirty,” Castro says, “they see how we live here and the situation we are in.”