What Price is the Rainbow?

What do these three things—climate regulation, diarrhea, and water quality—have in common?

The surprising answer: intact forests.

Forests are famous for their vital role in storing carbon.  But new research is revealing equally critical benefits of forests in regulating the planet’s temperature and providing stable supplies of fresh water.  

The moisture from forests can be thought of as rainbow water because of its colors: green (water used and emitted by plants), blue (water we drink), and grey (water we waste).

Green Water

Most policy and legislation deals with the blue and grey part of the rainbow—the water we drink and waste.  

But that leaves out all the water from plants.  Via the process of evapotranspiration, which results from photosynthesis, forests emit trillions of tonnes of water into the atmosphere each year. 

This creates clouds that reflect sunlight back into space, reducing planetary warming.  And those clouds also produce vital rainfall.

For instance, at least 40 percent of the rainfall over land, and up to 50-70 percent of the rainfall in the Amazon, originates from forests.

Novel but controversial research even suggests forests might act as regional “biotic pumps”. As clouds build up over a forest and condense into rainfall, low-pressure systems are formed that suck rain-bearing coastal winds into dry continental centers.

But this pump only works if the forests between the coast and interior areas are intact.  If the forests are cleared or fragmented, then the biotic pump breaks down. 

If this idea is valid, then the value of intact forests for maintaining productive climates for farming, power generation, fisheries, the environment, and other values may be grossly underestimated.

Forests are also important for maintaining stable local climates.  Areas cleared for crops are from 1.5 to 6.5 degrees Centigrade hotter than those with intact forests, because the former lose much of their shade and evaporative cooling.  Such heating has major impacts on human health, diseases, and agricultural productivity.

Hot, dry conditions also lead to fire.  In 2015 alone, the blanket of haze that perennially covers much of Southeast Asia led to economic losses of up to $45 billion, and tens of thousands of premature deaths.

Blue Water

The West African nation of Malawi lost 14 percent of its forests in a decade.  In a scientific first, research showed a direct relationship between deforestation and clean drinking water.  The decline in clean freshwater was equivalent to a 9 percent reduction in rainfall.

The best-known case for the water-purifying role of forests is New York City.  Instead of a massive filtration plant, New Yorkers invested around a billion dollars by restoring forests in the nearby Catskill mountains.  

The Catskill forests cost just a fraction of a high-tech approach to water filtration.  And how well did it work?  Now, more than 140 cities around the U.S. are considering similar watershed conservation rather than building expensive filtration systems.

The largest cost-benefit analysis ever conducted in the tropics also found that forests, even selectively logged ones, are a highly cost-effective way to produce clean water.

Intact Forests are Healthy

There are also clear pathways from deforestation to human sickness.   

In Cambodia, deforested areas have a markedly higher incidence of diarrhea.  The same seems to be true in Flores, Indonesia.  And in Borneo, deforestation is leading to an increase in malaria. 

One key reason is the heating of once-shady forest floors.  This increases the temperature of pooled water, which promotes breeding of mosquitoes—the most important disease vectors.  

There are also fewer trees to transpire water, so the ground becomes swampy and more likely to sustain disease.

And as loggers and developers penetrate ever-deeper into forests, they inevitably encounter new pathogens endemic to remote areas.  The Zika virus emerged from the forests of Uganda.  Dengue, Chikungunya, and Yellow Fever also likely came out of African forests.

So, what price is the rainbow and the intact forests that sustain it?

Nothing less than life itself.