Leveraging Nature and Tools from the Past for the Future of Water Security in the Andes
Bonnesoeur, V., B. Locatelli, M.R. Guariguata, B.F. Ochoa-Tocachi, V. Vanacker, Z. Mao, A. Stokes, and S.-L. Mathez-Stiefel. 2019. “Impacts of Forests and Forestation on Hydrological Services in the Andes: A Systematic Review.” Forest Ecology and Management 433 (February): 569–84. doi:10.1016/j.foreco.2018.11.033.
Kinouchi, T., T. Nakajima, J. Mendoza, P. Fuchs, and Y. Asaoka. 2019. “Water Security in High Mountain Cities of the Andes under a Growing Population and Climate Change: A Case Study of La Paz and El Alto, Bolivia.” Water Security 6 (March): 100025. doi:10.1016/j.wasec.2019.100025.
Ochoa-Tocachi, B.F., J.D. Bardales, J. Antiporta, K. Pérez, L. Acosta, F. Mao, Z. Zulkafli, et al. 2019. “Potential Contributions of Pre-Inca Infiltration Infrastructure to Andean Water Security.” Nature Susatinability 2 (7): 584–93. doi:10.1038/s41893-019-0307-1.
Spanning from Colombia to Chile, the Andes mountains tower over small towns and bustling coastal metropolises. Many of these communities—especially those on the drier, western side of the mountains—have historically relied on runoff from the peaks above as a critical source of water for farming, industry, and municipal use. However, climate change and ecosystem degradation have begun to destabilize historical flow patterns causing both prolonged water insecurity and intense flooding. Compounding threats—shrinking glaciers, deforestation, and expanding urban development—make for an uncertain future of the region’s water supply.
Across the region, city planners and water managers are now looking to a diverse set of strategies to address these stressors. The region is beginning to move toward resilience to climate change through building capacity to predict future supply and demand, learning from Indigenous water management strategies and restoring natural ecosystems.
An illustrative example of a city facing emerging threats to water security in the Andes is El Alto, Bolivia. Located just west of La Paz, one of Bolivia’s two capital cities, El Alto is an expanding, high-altitude urban center largely reliant on glacial runoff for its water supply. In a recent study led by Dr. Tsuyoshi Kinouchi from the Tokyo Institute of Technology, a team of researchers sought to assess the vulnerability of El Alto’s water system to these challenges by coupling future projections of supply with the rising demand.
The study, published in Water Security, estimated El Alto’s future water supply under a variety of climate change scenarios. Under the most extreme scenario, the city’s water supply was projected to be lower and more variable due to both changes in precipitation patterns and decreased glacial meltwater. These estimates of supply were then paired with several projected future scenarios for water demand. Even under scenarios of slow population growth and improved water use efficiency, demand for water was expected to exceed the annual supply by 2023. This scenario will lead to growing water deficit in the city’s main water source, Tuni Lake, and potentially a need for water transfers from other sources. Replicating these analyses to model future water needs for other cities throughout the Andes will be a critical initial step in planning for climate adaptation strategies.
The dominant approaches to managing water scarcity issues in the Andes involves building expensive “gray infrastructure”, which includes dams and concrete flood drainage networks. However, new methods are gaining traction. Two of these promising strategies are managing natural ecosystems and using Indigenous water management practices alongside existing gray infrastructure.
In Peru, planners are looking to Indigenous water management systems as potential tools for managing future water problems. “Amunas”— meaning “retaining” in Quechua, the most widely spoken Indigenous language in the region—are a type of infiltration canal system that diverts water from fast-flowing mountain streams to run laterally across slopes during peak flows. By redirecting and slowing down flow, Amunas allow water to seep into the soil where it flows underground to feed mountain springs. These springs served as critical sources of water for irrigation in the dry season, allowing farmers to increase productivity. Due to their ability to channel water underground, Amunas have the added benefit of avoiding water loss to evaporation—a major problem faced by many modern artificial reservoirs.
Amunas implemented on a larger scale may help secure water supply for urban areas. In a recent study published in Nature Sustainability, a team of researchers led by Boris Ochoa-Tocachi at the Imperial College London sought to investigate the applicability of Amuna systems in the Rimac River Basin, one of the major water sources for Lima, Peru.
To better understand the effectiveness of Amunas, researchers first gathered data from a 1,400-year-old infiltration system in an agropastoral community high in the Andes about 100 km northwest of Lima. The researchers found that the system slowed water flows substantially after rainfall events. Water from upstream infiltration canals appeared anywhere from 2 weeks to 8 months later in downslope springs, providing a steadier supply of water in the dry season.
The researchers used the data collected from this small Amunas system to model the potential for scaling in the Rimac River Basin. Models indicated that implementing Amunas reduced average peak flows by 15 percent compared to gray infrastructure interventions alone; it also boosted flows over the drier summer months to meet Lima’s water demand. Because of the benefits that Amunas provide, SUNASS, Peru’s drinking water regulator, has used a tax-supported initiative to begin to restore Amunas in the watersheds that supply Lima. Combined with other ecosystem-based management strategies, including grassland conservation and sustainable agriculture practices, Amunas may become a key part of Lima’s future water security.
Similar to Amunas, other ecosystem-based management strategies, or nature-based solutions, are becoming increasingly important for building resiliency to climate change within the region’s water sector. In a systematic review of impacts of forests on hydrological services in the Andes, a team of researchers led by Vivien Bonnesouer aimed to synthesize the existing state of knowledge to better inform decision-making in the face of climate change. Their meta-analysis of studies covered ecosystem services such as landslide and erosion prevention, flood control, and water security.
The study, published recently in Forest Ecology and Management, found that increased forest cover and forest restoration practices improved ecosystem services in most cases. However, the location and species of trees planted was consequential to the hydrologic services, and increased forestation did not always have positive effects, especially in areas that were not originally forested. For example, non-native tree plantations planted in Paramos—a type of grassland in the high Andes—tended to reduce runoff substantially due to the high water demand of these trees. Results of the study highlighted that one-size-fits-all solutions cannot be universally applied over the diverse landscapes of the Andes.
As cites in the Andes prepare for increasing populations and a shifting of historic climate patterns, their water management systems will require an innovative combination of increased water use efficiency, nature-based solutions, and restoration of ancient infrastructure systems. Increased capacity to predict future water supplies and demand on a local level, complimented with specialized holistic management strategies catered to the specific ecology and topography of local environments, can help the region increase its resiliency to the changing climate. Cross-sectoral collaboration from investors, legislators, and local communities will be a necessary part of these solutions.