LIMA, Peru — As the second-largest desert city in the world, Lima has always needed to manage its water carefully. In recent years, climate change has made access to water even more challenging. By one estimate, the region deals with a yearly water deficit of 43 million cubic meters.
For seven months out of the year, the city of Lima has drastic water shortages. Many of Lima’s nine million residents find themselves without reliable running water for much of the year. During the December-to-May rainy season, Lima receives sufficient precipitation, but runs the risk of flash floods and landslides. The wet-dry cycle is becoming more and more drastic as climate change affects global weather patterns.
The city’s water utility company, Sedapal, has been working with Peruvian and American NGOs to find a cost effective solution to Lima’s problem. Bert De Bièvre, a hydrologist with Peru-based CONDESAN, told New Scientist, “The idea is to build a timelag into the hydrological system, delaying water run-off for weeks or even months until it benefits water supply in the dry season.”
Suggested methods to accomplish this have ranged from encouraging farmers to graze alpacas instead of cows in the Andes in an effort to keep the ground from becoming hard-packed and non-absorbent, to desalinization plants off the coast.
By far the most affordable option, however, is to revive the ancient system of amunas on the sides of the Andes mountains. Built by the Wari people several hundred years before the Inca civilization, these channels and pools are more than just an archaeological curiosity. It turns out that the Wari were surprisingly adept city planners, especially when it came to getting water during the dry season.
Amunas can have many forms, ranging from narrow trenches, to pools and even sometimes to structures that look like walls. Despite these structural differences, their purpose is uniform. All amunas are designed to keep rainfall from flowing immediately downhill. Instead, the amunas guide rainwater across the mountainsides, allowing the ground to absorb more and replenishing the water table.
Re-grouting the amunas with concrete will cost about $23 million, much less than any other plan offered. A study by CONDESAN and Forest Trends, a Washington, DC-based NGO specializing in green infrastructure, estimates that reviving the amunas could increase Lima’s water supply by 26 million cubic meters and decrease the dry season water deficit by as much as 60 percent.
This solution comes at an opportune time. Lima’s population is expected to grow past 10 million by 2030, according to a U.N. report. The growing population combined with the increasing threats of climate change make access to water that much more crucial. If Lima can solve its water problem, it will serve as a great teacher for other cities faced with water challenges.
– Marina Middleton