Medellin, Colombia - Scientists are finding a new suspect to blame for flood disasters around the world, and it’s not climate change: It’s sediment.
Researchers in Spain have found the number of yearly floods and related disasters around the world has jumped more than 9 times since the 1950s - to more than 180 per year - and that the trends in rainfall attributed to climate change are not enough to explain such a rise.
Instead, the dramatic rise of water-related disasters seems to follow GDP, the researchers found. As economies around the world grow, people are clearing more and more forests to make way for cities and farms. Without trees to retain soil, excess dirt and rocks are poured into rivers, damaging their capacity to cope with storms.
Sediments are produced when water, wind, ice or changes in temperature break up rocks and soil into small bits, in a process called erosion. Erosion is a natural process that shapes the landscape and transports nutrients.
However, human impacts on land - especially deforestation - have significantly increased erosion rates all around the world.
A 2010 study by the University of Cantabria in Santander, Spain and the Universidad Nacional de La Plata in Argentina looked at sediments and their connection with economic growth, using the La Plata River in South America as a case study.
The study found while unpopulated Andean regions showed no major increase in erosion, in places near the Sao Paulo metropolitan area sedimentations rates increased “gently” starting in the mid-1980s and then sharply since 2000, showing more than tenfold growth in about 20 years.
A 2012 follow-up study by the Earth Science Department at the University of Cantabria found that as GDP increased in northern Spain, so did the rates of sediment production, and also the number of water-triggered disasters in the region.
Colombia’s Magdalena River
The researchers’ hypothesis is that human contributions to erosion have risen to an extent that the world is now undergoing “global geomorphic change”, which makes floods and landslides worse, regardless of the changes in the weather.
The Magdalena River in Colombia is a dramatic illustration of the changes, and the inter-relationships between economic growth, sediments and flooding.
The Magdalena is born in the Colombian Andes, and flows north into the Caribbean Sea. More than 80 percent of Colombians live in the Magdalena Basin, and about 85 percent of Colombia’s GDP is generated there.
Once it was the swiftest way to move between cities in Colombia’s interior and the Atlantic Ocean. But current navigation on the Magdalena is very limited, partly because of excess sediments accumulated in the riverbed.
The Magdalena flooded in 2010 and 2011 when rainy seasons enhanced by the La Niña phenomenon caused the worst climate-linked tragedy in Colombian history, affecting more than four million Colombians. Two-and-a-half million became climate refugees. One million hectares of cropland were flooded, and more than 800 roads destroyed. The country spent more than $3.9bn in emergency humanitarian aid to cope with the tragedy. More
I have to question if this is partly to blame for the flooding in Pakistan in 2010 and 2011? Editor
