Want clean water? Save your forests!

Cities can ensure they have a cheap and abundant supply of clean water by protecting and regenerating forests in their surrounding watersheds, according to a major analysis just undertaken in Malaysia.

Forests are a vital source of clean water -- and important for lots of other reasons too.

Forests are a vital source of clean water -- and important for lots of other reasons too.

Jeffrey Vincent from Duke University, USA and his colleagues have just published the largest cost-benefit analysis ever conducted in the tropics, and they find that pristine and even selectively logged forests are very cost-effective ways to produce clean, drinkable water. 

Vincent and colleagues ran their analyses under a wide range of scenarios.  They used as a baseline the costs of standard water-treatment plants, which are often required to make polluted water safe to drink.

The authors found that the relative advantages of forests depend on local circumstances, with the financial benefits being greater in some situations than others. 

Also, if one factors in profits that can be made by exploiting the forests -- such as by converting them to agriculture -- then the numbers could change. 

The problem, of course, is that waters that drain off of agricultural lands are often polluted by fertilizers, pesticides, and organic wastes, making expensive water-treatment necessary.

The authors argue that, beyond water purification, intact forests have many other financial and non-financial values. 

For instance, they store large stocks of carbon, and thereby reduce greenhouse gas emissions. 

They also can harbor enormous biodiversity while helping to attract substantial income from ecotourism.  Remarkably, it's currently estimated that protected areas across the world attract some 8 billion visits annually, underscoring their financial value for local communities.

Furthermore, via the process of evapotranspiration, forests emit enormous quantities of water vapor.  For example, one-third to one-half all the rainfall that falls on a tropical forest is quickly recycled back to the atmosphere, as water vapor.

This water vapor (plus natural organic aerosols emitted from forests) help to form clouds, which in turn reflect solar radiation back into outer space, thereby reducing global warming. 

Forests are natural cloud-makers.

Forests are natural cloud-makers.

Such clouds also help to produce life-giving rainfall during the dry season -- when forests are most drought-stressed and prone to fires.

Finally, forests are very good at reducing destructive floods.  They tend to act like giant biological sponges, trapping water and releasing it slowly, thereby reducing downstream flooding.  Especially in areas where forests are denuded, flooding can cause billions of dollars in damage and costs thousands of lives each year.

The conclusion: It's increasingly becoming apparent that it's smart to conserve pristine and selectively logged forests -- even when one uses just hard, cold economic logic. 


Disaster ahead for Sumatra's forests?

Alarm bells are ringing in Indonesia. 

An in-depth article just published by ALERT member Erik Meijaard in the Jakarta Globe suggests that the Leuser Ecosystem in northern Sumatra — the last place on Earth where tigers, orangutans, elephants, and rhinos still coexist — could be greatly imperiled.

Trouble ahead for tigers

Trouble ahead for tigers

The problem is the highly controversial “spatial plan” passed by the Aceh Provincial Government. 

The plan completely omits the Leuser Ecosystem — and according to Meijaard that’s because the Aceh government plans to log, clear, mine, and essentially destroy much of the Leuser environment.

That would be a tragedy wrapped in a disaster.  The IUCN lists the Leuser Ecosystem — a region of 2.26 million hectares rich in rainforests and peat-swamp forests — as one of the “World’s Most Irreplaceable Places”.

Beyond its unparalleled importance for biodiversity, the Leuser Ecosystem also provides vital environmental services for the people of Aceh — such as reducing flooding and droughts, protecting soils, and providing clean water for people, agriculture, and fisheries. 

The forests also store large quantities of carbon essential for limiting global warming.

As Meijaard argues, the natural services provided by the Leuser forests truly are vital. 

For instance, floods in December 2006 affected over 700 villages in Aceh, destroyed over 4400 homes, and killed 47 people.  Damage from the floods was estimated to total US$210 million. 

Imagine the toll from such an event if the Leuser forests — which help to limit destructive flooding — had been largely destroyed.

Meijaard and many others — including 141 scientific, environmental, and social-rights organizations — are urging Indonesia’s federal government to strike down the Aceh government’s ill-advised spatial plan, as the plan can't proceed without federal approval. 

Let’s hope common sense prevails in Indonesia, before one of Earth’s most unique and important ecosystems is lost forever.

Growing evidence that forests reduce flood risk

In 2007, ALERT member Corey Bradshaw and colleagues published a high-profile global analysis that suggested forests reduce flood risk. 

A tropical torrent -- flooding in the Amazon  (photo by William Laurance)

A tropical torrent -- flooding in the Amazon (photo by William Laurance)

However, their analysis was instantly controversial -- lauded in some quarters and attacked in others -- in part because their study used complex statistical models rather than simple experiments or direct observations to draw their conclusions. 

Now a new study appears to provide key support for Bradshaw's assertions.  Working in Peninsular Malaysia, Jie-Sheng Tan Soo and colleagues have found strong evidence that areas with more native rainforest are less prone to damaging floods in the wet season.

Specifically, the authors found that conversion of native rainforest to oil palm or rubber plantations increased the number of days of downstream flooding in 31 different areas.

Collectively, these findings are important because they provide another key economic justification for conserving native forests -- including pristine forests and those that have been selectively logged but still retain much of their original tree cover

Not only do such forests harbor amazing biodiversity, store large stocks of carbon, and help to drive global climate and rainfall patterns, they also have a sizable impact on flooding -- which is vital to local communities in forested regions.

Each years, destructive floods cause billions of dollars in damage to properties, crops, and livestock.  They also kill hundreds of people and displace tens of thousands more. 

With our growing human population and increasing tendency to live, build dwellings, and farm in vulnerable floodplains, floods are becoming an ever-more serious hazard. 

The poor are often forced to live in vulnerable flood-prone areas

The poor are often forced to live in vulnerable flood-prone areas

The poor -- which are often forced to live in flood-prone areas -- are especially vulnerable.  But we all suffer from flooding via increased insurance rates and higher taxes for government disaster-aid efforts. 

With the added complications of rising sea levels and increasing extreme-weather events, flooding might cost the world $1 trillion per year by 2050, according to one analysis.

The studies by Bradshaw, Tan Soo, and colleagues show that native forests can be vital for reducing flooding in regions that receive even occasional heavy rains. 

Less native forest means more destructive flooding -- and that's not good for any of us.

Forests reduce flooding

A longstanding debate in hydrological science is the degree to which forests actually limit downstream flooding.  Now a mega-study in Panama provides the strongest direct evidence to date that forests do indeed soak-up massive amounts of rainfall and then release it gradually over time.

Destructive floods cause billions of dollars of damage and likely kill thousands of people each year.  An earlier, global-scale statistical analysis suggested forests do indeed limit flooding and now the Panama experiment seems to seal the case.

The message is clear: retain forests to reduce floods

A torrent in the central Amazon  

A torrent in the central Amazon