Deforestation and Floods: A Deadly Combination


Last week’s mudslides in Colombia are a grim reminder of what can happen when the earth moves in ways we didn’t expect. Hundreds have died and hundreds more are still missing after heavy rains on Friday, March 31, caused three rivers to overflow their banks. The slides occurred in and around the city of Mocoa in the southwestern part of the country. You can see photos here.

The country’s president, Juan Manuel Santo, blamed the mudslides at least in part on climate change, saying the region received heavier than normal rainfall—about a third of what it normally gets over the course of a month in a single night. The ground was already saturated from heavier than average rains. The floods washed away homes, vehicles, roads, and at least two bridges, complicating evacuation and rescue efforts. Other contributors to the mudslides are the hilly terrain and, unfortunately, years of deforestation that left the hillsides vulnerable.

This isn’t the only time Colombia has experienced mudslides. Storms and the subsequent landslides in 2015 killed 80 people in the northern part of the country.

Rainforest once covered 80% of the country, and it’s estimated that 10% of the world’s species are found there. Currently a little more than half of the country is forested. The trees have been lost lo several different forces: agriculture and livestock, including illegal coca crops used to produce cocaine; an expanding population; energy-producing activities and mining; and logging. Wildfires have also taken a significant toll.

One program that might help limit deforestation is REDD (“reducing emissions from deforestation and forest degradation”), which is also active in other South American countries including Peru. You can read more about REDD’s efforts in Colombia here. EC_bug_web

  • Dan Waldman.

    Reckless logging and otherwise poor land use practices are the culprits here. A quick look at Google Earth shows that the town mentioned (Mocoa, Columbia) is situated down near a river bed (like most towns) and most of the uphill native vegetative cover in the surrounding watershed has been stripped away. We’ve seen this happen again and again – it’s not heavy rains or mudslides that are killing people and burying entire villages – it’s what we’re doing to the land that makes it so vulnerable to accelerated erosion…

  • Edo McGowan.

    Dan is quite correct. This resultant damage is seen globally where there is enough topographic relief to see unprotected saturated soil start to slip. In Rwanda, it is entire sides of the mountain, this stemming from inappropriate agriculture by stripping protective forest. These mud avalanches will pick up a number of towns on the way down, splat out in the valley below. Thus both the side of the mountain and the valley bottom are lost from production and this sees yet more forest cut to make up for the loss of agricultural production. In Malaysia, it is from stripping forest to make golf clubs. The damage extends to silting the reproductive habitat for fisheries. In Madagascar, it is from, again, inappropriate agriculture. The tongue of silt reaching out from Madagascar into the ocean for miles can be seen on satellite data. In the US, its also spreading antibiotic resistance from eroding areas where sewage sludge (biosolids) has been applied to forested areas. Biosolids are a serious source in the uncontrolled spread of antibiotic resistance. In forest areas where biosolids are applied, especially on fractured crystalline bedrock, reaches the drainage, which can extend within the fracture fabric for miles and move antibiotic resistant genes into down-gradient wells. These processes of water movement in fractured bedrock systems can include “megawaterheds.” Movement can be quite distant from the origin of the land applied sewage sludge (biosolids).

    Dr Edo McGowan


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