Water scarcity in the Andes: impact of population growth

17 July 2012

Source: American Geophysical Union (AGU)

Population growth poses an imminent threat to the supply of water to key urban cities in the Andes, and will significantly exacerbate the impacts of climate change upon water security, according to a new study. 

Population and climate change threaten water security

As the Earth's surface warms, climate models predict that the amount of fresh water for human consumption will likely decrease in parts of the globe. While that prospect looms for many cities around the world, a new study finds a more imminent threat to water supplies of cities in the tropical Andes, such as Lima, Peru and Quito, Ecuador.

"Despite all the uncertainty of the future impact of climate change, the impact of population growth is much bigger," said Wouter Buytaert of Imperial College London, an environmental engineer and lead author of the study. This could mean harsher times ahead for millions including the 7.6 and 2.2 million inhabitants of the fast growing cities of Lima and Quito.

Some parts of the tropical Andes, a region along the northwestern coast of South America, already lack sufficient water to meet demand. To help policy makers combat this water scarcity, Buytaert and his colleague, Bert De Bièvre of the Consortium for the Sustainable Development of the Andean Ecoregion in Quito, Ecuador, compared the two main drivers of water depletion in that region – climate change and population growth.

Population growth poses the greatest threat

The scientists used 19 climate models to project how climate change may affect urban water resources of the tropical Andes over the next 60 years. The models focused on four cities in the tropical Andes: Lima; Quito; Bogotá, Colombia; and La Paz, Bolivia. These four cities are all increasing in population at a faster rate than the average population growth rate of South America as a whole.

While the most pessimistic findings from models projected an average water depletion of up to 10 percent of current values, some optimistic outlooks estimated a 10 percent increase in water availability.

When the researchers separately modeled the impact of population growth, they found a drop of 38 to 62 percent in the amount of water available for each person. In their projections, the demand for more water as populations increase surpasses the amount of water lost through evaporation from warmer temperatures due to climate change.

Combining the two effects into a more realistic scenario of climate change and population growth happening simultaneously, the team saw the downward trend take over.

"Under whatever climate scenario, if you combine it with the impact of population growth it’s nearly certain that the impact will be negative," Buytaert said. "So, it's very, very unlikely that there will be more water available in the future [for this region]."

The study has been accepted for publication in Water Resources Research, a journal of the American Geophysical Union.

This article, published by the American Geophysical Union, has been reproduced by PSN. Minor changes and cuts may have been made for the purpose of brevity and relevance.