By Jesse Dykstra 21/12/2010 2


Can We Blame Climate Change for Flooding in Venezuela & Colombia?

In recent weeks, the wettest rainy season in over 40 years has battered Colombia and Venezuela, with flooding and landslides claiming over 200 lives, forcing millions of people from their homes and inundating valuable agricultural crops. Over 1.6 million (nearly 4% of Colombia total population of 45 million) people have been displaced from their homes, primarily by flooding.

Venezuelan president Hugo Chavez has publicly blamed global climate change for the recent wet weather, pointing the finger at western-based “criminal capitalism” and overconsumption as the source of this latest natural disaster. Colombian president Juan Manuel Santos has described the events of recent weeks as an unprecedented tragedy for his country.

High rainfall isn’t unusual in the region. The mountainous topography of northern South America provides a barrier to trade winds from both the Pacific and Atlantic Oceans, forcing up warm, moisture-laden equatorial air currents. This generates potentially high rainfall in both the Pacific and Amazon regions, on either side of the continental divide. The town of Lloro in north western Colombia claims the highest average annual precipitation of any lowland location in the world, at 13.3 m.

Source: gaurdian.co.uk
Source: guardian.co.uk

This rainy season in Colombia has seen the heaviest rains on record. The result has been called the worst natural disaster in Colombia history. And like the flooding  in Pakistan earlier this year, it is the high degree of vulnerability of the people who live in Colombia and Venezuela that has resulted in the massive scale of this disaster.

The 1999 Disaster in Venezuela

Caraballeda_1999_Deposits_and_Damage_USGS
Caraballeda Venezuela, 1999. Source: USGS

Chavez should be familiar with the vulnerability of Venezuela’s growing population to natural disasters. In December 1999 (early in Chavez’s tenure),  heavy rainfall events with an estimated return period of 1 in 20 to 1 in 50 years saturated the rugged northern coast of Venezuela, inducing many landslides along the Cordillera de la Costa. Many of these landslides swept down steep slopes and coalesced into debris flows which rushed down the narrow valleys and spread out across the alluvial fans where most people live. These debris flows swept through towns and cities with little advanced warning, destroying over 8000 buildings and resulting in the deaths of up to 30,000 people. In the worst-hit area Caraballeda, up to 6 m of bouldery debris inundated much of the city.

Caraballeda is no stranger to debris flows, like many other towns and cities along the rugged northern coastline of South America. Often the only flat areas large enough to support the growing towns and cities in the region are alluvial fans at the base of steep gullies or river valleys, which naturally concentrate flood waters and debris during major storms. In fact, these fans generally exist because they have been created by thousands of years of episodic flooding and debris flow activity. In Caraballeda, which had a history of several damaging debris flows before 1999, a channel engineered to convey debris flows through the city safely was inadequate, and quickly became inundated.

Following the tragedy of 1999, a report by the United States Geological Survey (USGS) made the following suggestions for mitigating future risk:

  • implement flood control measures (e.g. check dams and channels to divert debris flows)
  • land-use regulations to limit developent in high-risk areas
  • use high-risk areas for open space use (e.g. parks, agriculture)
  • develop debris flow early warning systems

Of course, all of these things are economically costly, and require major government commitment. The gears of change turn slowly against political and economic resistance. In recent weeks, unstable saturated hillsides have mobilized again in Colombia and Venezuela, with landslides killing several hundred people in the region. Increased urbanization and agricultural intensification of river floodplains has left millions of people vulnerable to flooding.

Below is a short video of a landslide in Colombia , September 2010:

 

Vulnerability to Natural Hazards

We must resist the temptation to blame the heavy precipitation in Colombia and Venezuela, and subsequent disaster, on a changing climate. Rather, we should recognize that this disaster is the result of people living on land that is normally subject to natural hazards like flooding and landsliding. Instead of immediately pointing the finger at climate change, we should be asking; why are people still living in areas prone to flooding and landslides, despite prior experience and warnings to the contrary? What can be done to make these places safer in the future?

Unfortunately, there is no easy way to reduce the vulnerability of people in such regions. Many of the people caught by this disaster haven’t been able to choose where they live. Housing shortages, innafordability and growing urban populations mean that many people are forced to live in dangerous areas, such as in valley bottoms subject to innundation, or on unstable hillsides. However, fundamental changes to land-use planning and a committment to educating the public about  natural hazards may help to prevent such natural disasters in the future. If those issues aren’t addressed, regardless of whether or not climate change is driving more extreme precipitation events in Colombia and Venezuela, the region can expect a continued increase in the number and severity of natural disasters, as populations, and vulnerabilities increase.


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