South American Cities Face Flood Risk Due to Andes Meltdown

High above sea level, the mountains regulate water supply for millions in Colombia's cities, but natural flood control works are failing

By Autumn Spanne and DailyClimate.org

Deforestation and a changing climate high in the Andes can adversely impact Colombia's cities far below. Image: Flickr/Matthew Rutledge

BOGOT? ? Nearly a mile above this city of almost eight million is a rugged, fog-shrouded world, silent except for the trickle of water and whispering wind pushing through the treeless tundra. This is Chingaza, a national park 40 miles from Bogot? in the eastern range of the Colombian Andes.

Known as p?ramos, these ecosystems at more than 11,000 feet above sea level exist only in Central and South America, the majority in Colombia. P?ramos resemble a sort of alpine archipelago, each a link in the chain of distinct island ecosystems that have evolved in isolation to produce plants found nowhere else on the planet. They play a crucial role in maintaining a reliable water supply for millions of people in major cities like Bogot? and Medell?n. And along with the forests below, they protect those cities and the surrounding countryside from massive flooding.

One of the wettest countries on earth, Colombia's second rainy season of the year officially began in September. For the past two years, however, some parts of the country have had little respite from a destructive deluge during what are traditionally drier times of year.

La Ni?a ? the weather pattern that causes unusually cold ocean surface temperatures in the eastern Pacific ? has been blamed as the immediate culprit. But scientists believe climate change is also a factor in the flooding that has affected three quarters of Colombia in the past two years, cost billions of dollars and left hundreds dead.

As climate change converges with human encroachment in these mountains, the degradation of high Andean ecosystems is accelerating. And there are growing concerns that these costly floods will become a chronic problem even if climate change leads to sustained drought in the region.

P?ramos and cloud forests work as a finely tuned piece of ecological engineering that manages the flow of water from the high mountains to the lakes and rivers below. The p?ramos act as a sponge, absorbing and then conducting enormous quantities down the mountainside to the cloud forests. From there the water is further filtered and directed into rivers and reservoirs that quench the thirst of major urban areas without eroding the soil ? crucial in protecting against flooding.

The annual precipitation in Chingaza, which provides about 80 percent of Bogot?'s water, approaches four meters, or more than 13 feet, in some areas. Not all p?ramos are as wet as Chingaza, but they all have a vital role in both storing water and managing its flow.

"Well-preserved high-altitude lakes and peatlands help to protect lowlands from flooding by slowing down streamflows. After water purification, one of the most important regulating services of p?ramo...environments is flood control," said Daniel Ruiz, an associate professor of environmental engineering at Antioquia School of Engineering and researcher at Columbia University's International Research Institute for Climate and Society.

One of the most prominent features of p?ramos are large, silvery-green plants called espletia, more commonly known as frailej?n. The plant is ubiquitous, dotting the chilly landscape in some places as far as the eye can see. Its spiky clusters of leaves, reminiscent of some cacti, are covered in soft little hairs that catch moisture from the fog and funnel it into moss-covered soils that can hold several times their weight in water.

There are a variety of theories about how rising air temperature and altered precipitation patterns might affect these ecosystems in the future. But change has already arrived.

In 2011, the Inter-American Institute for Global Change Research and the Scientific Committee on Problems of the Environment released a joint report assessing climate change and biodiversity in the Andes. The report notes that the region is not just facing threats from future climate change, but already undergoing "significant shifts in temperatures, rainfall regimes and seasonal weather patterns."

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