Ranking world’s water towers

In a study published in Nature, which was led by Walter and Arthur, we ranked the Earth’s mountain ranges by their importance as ‘water towers’ and find that the most important water towers on the planet are also among the most vulnerable.

For this study, we identified 78 water towers and determined their importance in terms of their water supply and the demands they need to sustain. Based on state-of-the-art datasets we derived a Water Tower Index (WTI) reflecting each water tower’s importance. We also assessed each water tower to determine the vulnerability of the water resources, as well as the people and ecosystems that depend on them, based on projected future climate and socioeconomic changes, governance effectiveness, water stress, and potential for hydropolitical tension.

The Water Tower Index (WTI), the population in Water Tower Units (WTUs) and their downstream basins. The WTI is shown for all 78 WTUs, in combination with the shaded total population in all WTU-dependent river basins. Labels indicate the five water towers with the highest WTI value per continent. The insets show the number of people living in WTUs as a function of elevation and of the downstream population’s proximity to the WTUs.

Globally, the most relied-upon mountain system is the Indus water tower in Asia, according to their research. The Indus water tower (Hindu Kush, Karakoram and Himalaya) covering portions of Afghanistan, China, India and Pakistan is also one of the most vulnerable. High-ranking water tower systems on other continents are the southern Andes, the Rocky Mountains and the European Alps.

We conclude that it is essential to develop international, mountain-specific conservation and climate change adaptation policies and strategies to safeguard both ecosystems and people downstream. 

This research was supported by National Geographic and Rolex as part of their Perpetual Planet partnership. The Water Tower Index can be explored here in an interactive application created by National Geographic.

Two women tend their potato field in the Chipursan valley. This region is part of the Indus water tower, which, according to research supported by the National Geographic and Rolex Perpetual Planet partnership, is the most relied-upon glacier-based water system in the world (Photo by Matthew Paley, National Geographic)

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