Myths about forests and floods


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Earlier this year, floods in China killed more than 3,650 people and caused billions of dollars in damage. The international media and others blamed deforestation and logging for much of the destruction. In response, the Chinese government took strong action. It stopped all logging in old-growth forests in central and southern China and plans to phase out logging in other regions. Newspaper accounts report this could put as many as a million people out of work. It will also have a major affect on world forest product markets.

But did forest destruction really contribute to the floods? Recent papers by Ian Calder from the University of Newcastle and Ken Chomitz and Kanta Kumari from the World Bank suggest probably not.

Calder prepared his paper, titled ’Water-Resource and Land Use Issues’, for the International Water Management Institute. It reviews the evidence on how forests affect rainfall, runoff, water flows, erosion, water quality and floods from a largely hydrological perspective. It concludes ’There is little scientific evidence to support anecdotal reports of deforestation causing increased floods.’

Calder acknowledges that theoretically forests should reduce floods by allowing water to soak into the soil, rather than running off immediately towards the rivers. However, these effects would be expected to be less significant for large storms.

Chomitz and Kumari’s World Bank paper ’The Domestic Benefits of Tropical Forests, A Critical Review Emphasizing Hydrological Functions’ discusses these issues from an economic perspective. They look at the same issues as Calder, as well as other non-timber benefits forests provide.

On the issue of floods, they conclude that ’the scientific literature supports a link between deforestation and flooding only at a local level – within a drainage basin of less than about 50,000 hectares…In small watersheds, increases in water yield translate directly into increases in storm flow. For larger drainage basis, however, the limited number of available studies using long time series on floods show no link between deforestation and flooding.’

Both papers emphasize the need for further research. Calder’s paper also notes that ’the management activities associated with forestry such as cultivation, drainage, road construction, and soil compaction during logging are more likely to influence flood response than the presence or absence of the forests themselves.’


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Further reading

Calder’s paper can be found at the website:

If you do not have full internet access or have difficulty pulling down or printing the paper from the web, you can request a copy from Jim Lenahan at:

You can send comments to Ian Calder at:

Calder also has a forthcoming Earthscan book titled ’The Blue Revolution - Land Use and Integrated Water Resources Management’ that examines these issues in more detail.

To obtain an electronic copy of the Chomitz and Kumari paper you can write Tourya Tourougui at:

You can send comments about this message to Ken Chomitz at:

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