Native forests reduce the risk of catastrophic floods

20 08 2008
© Y. Agung (KOMPAS)

© Y. Agung (KOMPAS)

Each year extreme floods kill or displace hundreds of thousands of people and cause billions of dollars in damage to property. The consequences of floods are particularly catastrophic in developing countries generally lacking the infrastructure to deal adequately with above-average water levels.

For centuries it has been believed that native forest cover reduced the risk and severity of catastrophic flooding, but there has been strong scientific debate over the role of forests in flood mitigation.

Forest loss is currently estimated at 13 million hectares each year, with 6 million hectares of that being primary forest previously untouched by human activities. These primary forests are considered the most biologically diverse ecosystems on the planet, but this realisation has not halted their immense rate of loss.

Last year my colleagues and I published a paper entitled Global evidence that deforestation amplifies flood risk and severity in the developing world in Global Change Biology (highlighted in Nature and Faculty of 1000) that has finally provided tangible evidence that there is a strong link between deforestation and flood risk.

Using data from 56 developing nations in Central/South America, Africa and Asia, we correlated information on flood frequency and severity with country-specific forest data. After controlling for differences in rainfall, elevation, soil moisture and degraded areas, flood risk was strongly correlated with increasing deforestation. The models constructed predicted a 4 – 28 % increase in flood frequency with only a 10% increase in deforestation.

An important additional finding was that only the amount of native forest was correlated with reductions in flood risk – plantation forests had the opposite effect. This has huge implications for governments of developing nations trying to save lives and reduce expenditures. Promoting native forest conservation also has the added benefits of slowing climate change by storing vast quantities of carbon, reducing wildfires, and conserving species.

The study also investigated how deforestation affects the severity of flooding. We examined flood duration as an index of damage potential, as well as direct measures such as the number of people killed and displaced by floods, and the total estimated damage measured in dollars caused by powerful flood waters.

Although the correlations were not as strong, we found real evidence that deforestation also leads to more intense and devastating floods that kill more people and damage more property.

The implications of this study are measured potentially in the trillions of dollars over the next coming decades, so we hope it is used wisely as yet another good reason why we should preserve forests.

CJA Bradshaw

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12 responses

7 02 2014
Incentivise to keep primary forests intact | ConservationBytes.com

[…] replace primary vegetation, both in terms of biodiversity value and other ecosystem services (e.g., flood mitigation and carbon storage). While restoration is essential given the extent and rate of primary forest […]

4 08 2012
The invisible hand of ecosystem services « ConservationBytes.com

[...] prophet of Steve’s. Whether that be how much the probability (and therefore, costs) of flooding increases as deforestation occurs, or how much carbon is released into the atmosphere after logging, we need solid, quantified [...]

30 12 2011
Olivia Wilde

Just one more reason to stop deforestation! We’ve got to learn to live within nature rather than trying to overcome it.

30 12 2011
CJAB

The concept of ecosystem services is lost on most people – we need humanity to understand that destroying natural systems erodes our own lifestyle and prospects.

17 01 2011
Deforestation partly to blame for Queensland floods « ConservationBytes.com

[...] many of you might know, my colleagues and I wrote an article a few years ago about the global-scale evidence for deforestation leading to a higher incidence and severity of floods in the developing world. This was fairly controversial, but it was nonetheless the first [...]

9 12 2009
Breaking the waves – conservation conundrum of bioshields « ConservationBytes.com

[...] coastal ecosystems in the name of disaster management, (2) I have a professional interest in the ecosystem integrity-disaster interface and (3) I had the pleasure of editing this [...]

13 07 2009
Global conservation priorities based on human need « ConservationBytes.com

[...] divided the world by catchments (watersheds) and then estimated the services of water provision, flood prevention and carbon storage that each provides to humanity. Water provision was a estimated as a complex [...]

10 11 2008
Corey Bradshaw

Hanoi suffers as Vietnam flood toll rises to 55

Funny (i.e., sad). No mention of how deforestation increases flood risk, despite Vietnam having one of the highest rates of deforestation in the world.

27 08 2008
Forest Policy Research » Blog Archive » 389 Forest-Type / World-Wide

[...] 33) And I published a paper entitled Global evidence that deforestation amplifies flood risk and severity in the developing world in Global Change Biology (highlighted in Nature and Faculty of 1000) that has finally provided tangible evidence that there is a strong link between deforestation and flood risk. Using data from 56 developing nations in Central/South America, Africa and Asia, we correlated information on flood frequency and severity with country-specific forest data. After controlling for differences in rainfall, elevation, soil moisture and degraded areas, flood risk was strongly correlated with increasing deforestation. The models constructed predicted a 4 – 28 % increase in flood frequency with only a 10% increase in deforestation. An important additional finding was that only the amount of native forest was correlated with reductions in flood risk – plantation forests had the opposite effect. This has huge implications for governments of developing nations trying to save lives and reduce expenditures. Promoting native forest conservation also has the added benefits of slowing climate change by storing vast quantities of carbon, reducing wildfires, and conserving species. The study also investigated how deforestation affects the severity of flooding. We examined flood duration as an index of damage potential, as well as direct measures such as the number of people killed and displaced by floods, and the total estimated damage measured in dollars caused by powerful flood waters. Although the correlations were not as strong, we found real evidence that deforestation also leads to more intense and devastating floods that kill more people and damage more property. The implications of this study are measured potentially in the trillions of dollars over the next coming decades, so we hope it is used wisely as yet another good reason why we should preserve forests. http://conservationbytes.com/2008/08/20/native-forests-reduce-the-risk-of-catastrophic-floods/ [...]

25 08 2008
Inundaciones at Forestlove - Participa

[...] de hacer un donativo a la Cruz Roja. Bien, pero aquí hay una propuesta que puedes hacer ahora: detener la deforestación. Los bosques nos protegen de las inundaciones: durante siglos se ha creído que la cubierta [...]

21 08 2008
Alluvioni… at Forestlove - Partecipa

[...] Ecco un’informazione sulle foreste che ancora non ho citato: le foreste ci proteggono dalle alluvioni [...]

21 08 2008
Floods… at Forestlove - Cometogether

[...] something about forests that I haven’t mentioned before: they protect you from floods. For centuries it has been believed that native forest cover reduced the risk and severity of [...]

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