The Nazca lines are one of Peru’s major tourist attractions. The line-drawn figures of birds, fish, monkeys and humans were traced in the loose sand of the Pacific coast by pre-Incan cultures well over a thousand years ago. The fact that they still exist is testimony to the extreme climate conditions of the area. The Peruvian coastal desert is one of the driest places on earth. It is a narrow strip of sand and rocks that extends for thousands of kilometres between the Atacama desert in the south and the Sechura desert in the north, squeezed between the Pacific ocean and the Andean mountain range. Yet despite the lack of rain, the region has been inhabited by pre-Incan cultures since as early as 1200 BC. The hot climate is ideal for agriculture, as long as you add the magic ingredient: water. Luckily, water is abundant, not as rainfall, but as dozens of rivers that descend from the steep and wet slopes of the Andes, and cross the arid coastal strip before discharging in the ocean. It is no wonder then, that the Nazca and other ancient cultures in the regions were experts in building advanced irrigating systems.
The irrigation system Chavimochic, near the city of Trujillo, is one of the largest of the country. It covers 485km2, and further extensions are under construction. The water source is the Santa river that originates in the Cordillera Blanca (which translates as white mountain range) in the Andes of central Peru. The mountain range gets its name from hosting the world’s largest extension of tropical glaciers. However, as a result of rising temperatures, these glaciers are melting at a rapid pace. It comes as no surprise that Peru and other mountainous countries in the world are very concerned about the impact of melting glaciers on their water resources, and the potential impact on major economic activities such as Chavimochic.
Tropical glaciers – what happens when they melt?
Tropical glaciers are among the least studied regions in the world. Assessing the impacts of glacial melt is complicated, because it involves a large number of different processes that need to be studied and quantified. Furthermore, working in such remote and extreme environments is logistically challenging. Instruments such as weather stations are prone to damage from the harsh climate, and cannot be serviced (or batteries replaced) easily. As a result, we understand very little about the current behaviour of tropical glaciers, and even less about how they will respond to future climate change.
Even so, it is clear that many of the glaciers in the Cordillera Blanca and elsewhere are shrinking fast. This has severe consequences for water supply because glaciers often act as natural reservoirs: they store water from snowfall for months and even years, and release it gradually as the bottom of the glacier melts. This storage is particularly important in regions like the Cordillera Blanca, where snow- and rainfall is concentrated in a few months per year, but glacier melt is most prominent during the dry season – which is also the warmest.
Glacial meltwater will impact small communities and capital cities alike.
Glaciers provide a lot of the river flow during the dry season, which is when it matters most for water users such as irrigation farmers. Most of this use happens downstream from the glaciers, where the glacier meltwater is diluted with other water sources, such as groundwater, and water from lakes and swamps. Indeed, many downstream water uses only get a small fraction from the glaciers. For Chavimochic for instance, it is typically only around 20%. Yet, this fraction may be crucial. The rivers that supply water for Lima, the capital of Peru, only receive a few percentages of glacier meltwater. However, as a desert city with around 10 million inhabitants, the city is under acute water stress, and a decrease in water availability of 1 or 2% can make a difference for thousands of people.
On the other hand, as a major city with a thriving economy, Lima can invest in new infrastructure such as storage reservoirs and purification plants. This is not the case for small and poor farmer communities in the highlands. They often depend on much larger quantities of glacier melt, and lack the resources to adapt to changing water conditions. Additionally, agricultural practices in these communities are often intimately linked with their cultural heritage, and include methods and customs that have been passed on for generations. Changing them to adapt to the impacts of future climate change may be socially disruptive and unwelcome.
Finding a solution is no easy feat
Assessing the vulnerability of water resources to melting glaciers and designing adequate adaptation strategies is a major challenge – and an interdisciplinary one. We need glaciologists to better understand how glaciers will behave under future climate and how they release water in the mountain rivers. We need hydrologists to trace the glacier meltwater through the terrestrial water cycle to the point where the water is used. We need water resources economists to understand the economic impact of changes in water availability, and engineers to design technical solutions to reduce water use and explore new sources. Lastly, we need social scientists and anthropologists to assess which of those solutions are socially acceptable and least disruptive for local customs and cultures.
For this reason, the Peruvian government is setting up an international collaboration of researchers with the UK Natural Environment Research Council. On World Water Day 2018, I will be joining a group of UK and Peruvian scientists to visit the glaciers of the Cordillera Blanca, aiming to build the research links needed to tackle such a major research challenge. If successful, then it will help protect the Nazca vision of a green desert full of trees, birds and flowers.
Find out more about our work on water security and flood risk.
Read Wouter Buytaert’s briefing paper: Citizen science and web-based modelling tools for managing freshwater
