Lima is located in a narrow trip of coastal desert squeezed between the Pacific Ocean and the Andean cordillera. It is one of the driest places in the world, yet it is the country’s economic backbone. Lima is home to almost one third of Peru’s population and it dominates national industrial production and consumer spending. Up and down the coast, vast stretches of irrigated agricultural land that produce all-year-round asparagus, avocados, berries, and other high-value crops that are exported to the supermarkets of Europe and America.

The water needed for all this activity is abundant because of the adjacent mountain range, which functions as a natural water tower. When air masses from the Pacific hit the Andes, they are uplifted and generate rainfall. Together with spillover rainfall from the wet Amazon basin, this moisture feeds the rivers that run off to the coastal plains, where they provide water for the city and the agricultural irrigation systems. But there is a major problem with this supply: it is overabundant in the winter and spring, but it dries up to a trickle in the dry season of summer and fall.

Up in the humid highlands, smallholder farmers make a living from cattle grazing and growing crops such as potatoes and beans. They use water from the hundreds of small streams that eventually feed into the major rivers supplying the coastal desert. But, in using this water, they also need to safeguard downstream water supplies. On the steep slopes of the Andes, soils are very prone to degradation and erosion. Compacted and damaged soil cannot absorb and store water very well, leading

to higher rates of runoff and high peak flows laden with sediment that clogs downstream irrigation reservoirs and canals. To avoid this, farmers need to to be active in reforesting slopes, protecting wetlands, and adopting soil conservation strategies. Their challenge is to find a precarious balance between generating sufficient income for themselves, while protecting the downstream water resources.

The farmers and CONDESAN installed hydrological monitoring equipment in two mountain streams descending from the grazing lands. Then, they closed off one watershed to all cattle.

With the scientific support of an international research group, they were able to look at different scenarios, to help find the ideal balance between cattle grazing and streamflow.

With scientific support to quantify the potential impact of mamanteo, the community decided to refurbish some of the old canals. CONDESAN, added small quantities of dye to water in the canals, to track its movement and quantify the travel time of

water down the hillslope. These data were combined with a hydrological model to assess the potential for increasing streamflow during the dry season.