The 1,400-year-old invention Peru is reviving

Pre-pandemic, in the austral winter, I drove north out of Lima, up into Peru's highlands to the village of Huamantanga (wa-mon-TONG-a). I was traveling with scientists who were studying local farmers' use of a 1,400-year-old technique to extend water availability into the long dry season.

Wending our way through the narrow Chillón River Valley, a slim swath of irrigated green crops hemmed in by sheer walls of tawny rock, we crossed the river and began grinding up a single-lane dirt road clinging to the side of a steep mountain. At about 3,500m (11,500ft), we reached a plateau with fields of avocados, hops, potatoes and beans and, finally, the village, where two-storey buildings of mud bricks and concrete lined narrow dirt streets. Burros, horses, cows, dogs and people puttered around.

The Andes Mountains are one of six places in the world where complex civilisations emerged, spurred by precipitation so seasonal it was a catalyst for hydrological innovations again and again. People cultivated deep knowledge of water and the underground, deploying strategies that still astonish – and which some still use.

Today, modern Peruvians are redeploying that ancient knowledge and protecting natural ecosystems such as high-altitude wetlands to help the country adapt to climate change. It's one of the world's first efforts to integrate nature into water management on a national scale.

Peru is among the world's most water-insecure countries. The capital Lima, home to a third of the country's population, sprawls across a flat desert plain and receives just 13mm (0.5 inches) of annual rainfall. To support that human abundance, it relies on three rivers born in the Andes that rise behind the city, soaring to 5,000m (16,400ft) in just 150 kilometres (93 miles). Lima residents are not alone in this reliance on mountain water. An estimated 1.5 billion people worldwide could depend on water flowing from mountains by 2050, up from 200 million in the 1960s.

Water scarcity in Peru is getting worse as a result of climate change. Within living memory, mountain glaciers have melted and the rainy season has shrunk to just a couple of months. Already Lima's water utility Sedapal can only supply customers 21 hours a day, a rate that Ivan Lucich, executive director of the national water regulator Sunass, says he expects to further decline in the coming years. A 2019 World Bank report evaluating drought risk in Peru concluded that the capital's current strategies to manage drought – dams, reservoirs, storage under the city – will be inadequate by as early as 2030.

Several years ago, desperate for water security, the country's leaders did something radical: they passed a series of national laws requiring water utilities to invest a percentage of their customers' bills in “natural infrastructure”. These funds – called Mechanismos de Retribucion por Servicios Ecosistemicos (Mechanisms of Reward for Ecosystem Services) or MRSE – go to nature-based water interventions, such as restoring ancient human systems that work with nature, protecting high-altitude wetlands and forests, or introducing rotational grazing to protect grasslands. Before, it was considered a misuse of public funds if utilities invested in the watershed. Now it's required.

As climate change brings water change worldwide, conventional water control structures are increasingly failing. Such human interventions tend to confine water and speed it away, erasing natural phases when water stalls on land. Nature-based solutions, on the other hand, make space and time for these slow phases. In researching my forthcoming book on the subject, I've come to think of them as “slow water”. Like the slow food movement, slow water approaches are bespoke: they work with local landscapes, climates and cultures rather than try to control or change them. They provide multiple other benefits too, including carbon storage and homes for threatened plants and animals.

For these reasons, conserving wetlands, river floodplains and mountain forests for water management is a growing movement worldwide, including among institutions such as the United Nations and the World Bank. But most projects to date are small and disconnected, so people tend to think of them as attractive side features, rather than a key tool. It's akin to the long-held attitude toward solar and wind power that is swiftly becoming outdated: they're nice but were thought not to be capable of playing a major role in meeting our energy needs. Peru's national programme, however, has the potential to demonstrate how effective slow water solutions can be when implemented on the scale of watersheds.

Yet despite Peru's forward-thinking policies, putting it into practice has been slow going, due in part to high turnover in government – including five presidents in five years. Another big hurdle, and one that most countries face: overcoming ingrained practices in the water sector to try something new.

In 2018, Global Affairs Canada and the United States Agency for International Development pledged to invest $27.5m (£19.6m) over five years to help Peru get its innovative programme off the ground. The money went to Forest Trends, an NGO that has been working on nature-based solutions for water in Peru since 2012. The executive director of its Lima office, Fernando Moimy, has long championed the idea, first in government as the former chief of Sunass, then via Forest Trends. The NGO's initiative, called Natural Infrastructure for Water Security, aims to provide technical know-how, says Gena Gammie, deputy director of the project.

Now the effort is gaining momentum. Forty of the country's 50 water utilities are collecting MRSE funds and have raised more than $30m (£21m). Sunass expects them to raise at least $43m (£31m) by 2024. That money is being invested in more than 60 projects across the country. Among those being supported by Lima's water utility Sedapal are projects shoring up an ancient water storage technique and protecting rare, high-altitude cushion bogs.

Planting the water

This is what had brought me on the precipitous journey through the Peruvian highlands north of Lima, to the village of Huamantanga, with scientists studying the region's age-old water management techniques.

The people who live here are comuneros: members of an agricultural collective. They use water canals called amunas – a Quechua word meaning “to retain” – to divert wet-season flows from mountain streams and route them to natural infiltration basins. The strategy, invented by an ancient people called the Huari (WAR-i), is still practiced here and in a few other Andean villages. Because the water moves more slowly underground as it travels through gravel and soil, it emerges downslope from springs months later, when the comuneros collect it to water their crops. Because much of their irrigation soaks into the ground and eventually makes its way back to the rivers that supply Lima, repairing abandoned amunas scattered throughout the highlands could extend water into the dry season for city dwellers too. Hence Sedapal's interest.