Understanding the future of the Andean Water Tower

Written by Owen King

The consequences of high mountain deglaciation

The loss of ice from the planet’s high mountain environments is one of the most vivid visual examples of the impact of climate change on the natural environment. Glaciers have receded and thinned, in some cases to the point of extinction, in many of Earth’s mountain regions in recent decades, and the rate of ice loss continues to increase at the global scale.

Between 2000 and 2019, glaciers (excluding the polar ice sheets) lost an average of 267 ± 16 gigatonnes (billions of tonnes) of ice per year. The meltwater produced by this ice loss was responsible for ~21% of the observed sea level rise over the same period (Hugonnet et al., 2021).

The retreat of glaciers from mountain environments has huge implications for the sustainability of freshwater resources, the threat posed by geohazards associated with glacier meltwater, and ecosystem preservation across some of the planet’s most populous regions.

Decreasing water supply

The term ‘Water Tower’ is often used to describe the supply of freshwater from the planet’s mountain regions, which is heavily relied upon for drinking, crop irrigation, hydropower and industry further downstream. Glaciers have typically contributed a substantial, and dependable, component of this freshwater output from the mountains on an annual basis.

As glacier melt rates have increased over the last few decades, this contribution to river flow has also increased. However, as glacier volume declines past a certain point, their contribution to the water tower budget also reduces (Huss and Hock paper). The transition from increasing to diminishing glacier meltwater yield is commonly described as ‘Peak Water’. The passing of the point of Peak Water increases Water Tower vulnerability (Immerzeel et al. 2020) and water resource stress in populations downstream.

Growth of glacial lakes

The excess production of glacier meltwater has also driven the formation and expansion of thousands of glacial lakes high in the planet’s mountain regions, which have increased in number by 53% since 1990 (Shugar et al., 2020). These lakes occupy locations formerly covered by glaciers, and are commonly dammed by unconsolidated glacial sediment and debris (moraines), which are prone to degradation and failure.

If glacial lakes drain suddenly, Glacial Lake Outburst Floods (GLOFs) can impact communities considerable distances downstream. A recent study by researchers based at the School of Geography, Politics and Sociology at Newcastle University estimated that as many as 15 million people are exposed to GLOF impacts around the world (Taylor et al., 2023).

Lago Cachet Dos in Patagonia, southern South America, has repeatedly drained and refilled in recent times. During a GLOF event, water drains in subglacial conduits beneath the Colonia Glacier. Note stranded icebergs are lake drainage. Imagery: GoogleEarth, Edited by J.Bendle.

Water resources in the Andes

The South American Andes is a mountain region which is particularly prone to the water resource and geohazard challenges described above. Considerable portions of the population of these mountains reside in river catchments where the point of Peak Water contribution by local glaciers may have already passed (Huss and Hock paper), and up to 17% of the regional population are exposed to GLOF hazards (Taylor et al., 2023).

Glaciers in the Andes have lost 21.4 ± 2.1 gigatonnes of ice per year since the millennium (Hugonnet et al., 2021), the rate of which has increased throughout the last two decades. The evolution of the Andean cryosphere needs to be clearly quantified if we are to understand the future of the river systems the water tower feeds.

Lake Palcacocha, Peru. Image credit- Dr Bethan Davies, Newcastle University

Reconstructing glacier change

In a new project (Deplete and retreat), researchers including Dr Bethan Davies and Dr Owen King from the School of Geography, Politics and Sociology at Newcastle University, aim to establish how glaciers in ten mountain catchments along the length of the Andes have evolved between ~1850 and the present day.

To reconstruct glacier volume, a combination of techniques can be used to document changes in glacier extent preserved in the landscape and changes in glacier surface height. By mapping the geomorphological signature left on the landscape by glaciers at their former, larger extent, when the earth’s climate was cooler, the project will be able to establish the volume of glaciers throughout the Andes as far back as 1850.

By analysing satellite images acquired as far back as the 1960s, the project will also quantify changes in glacier surface height over the last six decades. Typically, detailed measurements of glacier fluctuations based on satellite images are restricted to the period since the millennium. By using recently declassified spy satellite images acquired during the Cold War, the Deplete and Retreat project will be able to extend these observations further back in time, revealing changes experienced by Andean glaciers which have so far not been documented. These long-term records of ice volume fluctuations provide information on the sensitivity of glaciers to a changing climate.

Reconstructing climate

A second part of the interdisciplinary project is understanding how climate is, and how it will, change, across the Andes. This is a challenging topic, because of the steep mountains and the complex topography. One great challenge is the shortage of automatic weather stations at high altitudes. To improve our ability to understand climate across the Andes, the team will strategically deploy automatic weather stations at high elevations, where there is a particular shortage of data.

These stations will be set up in partnership with colleagues from South America, who will help to maintain and manage the weather stations in the future. The data from these weather stations will help to improve high resolution climate models, which a team from the University of Sheffield will develop.  

Simulating glacier behaviour and meltwater yield

Finally, the project will use glacier and hydrological models to predict water resource changes in the Andes up to the year 2100, under various warming scenarios. These model simulations will be evaluated against our present-day observations and against our reconstructed glacier extents and volumes. Through close collaboration with project partners in South America, the findings of the project will have impact where it matters most, influencing water resource management strategies to minimise water stress felt by local communities.


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