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Watershed markets get a dose of myth-busting science

Virginia Gewin

From Mexico to Malaysia, payments for watershed service schemes are at a critical juncture right now as watershed managers work to transform them from publicly funded pilot programs into privately funded markets. Will watershed markets be able to make this all-important leap? The Ecosystem Marketplace looks at this question and highlights the importance of getting the science right when it comes to markets for watershed services.

From Mexico to Malaysia, payments for watershed service schemes are at a critical juncture right now as watershed managers work to transform them from publicly funded pilot programs into privately funded markets. Will watershed markets be able to make this all-important leap? The Ecosystem Marketplace looks at this question and highlights the importance of getting the science right when it comes to markets for watershed services. All your friends are raving about the latest ancient herbal remedy. From fevers to fatigue, it is touted as a panacea curing all ills. Sure, it's expensive, but you rationalize that your health is worth it. While it seems to help your friends, it affects everyone differently and nobody can tell you how it works. How do you know if the cure is right for you? Undoubtedly, buyers expect a return on their investment. But, what if the product (or service) for which you are paying is elusive? Take water. Complex processes-both natural and man-made– influence the quantity and quality of water, but forests, like that ancient herbal remedy, have taken on the mythical role as the sole prescription for improving watershed services. Around the world, in fact, tropical watershed conservation initiatives based largely on this idea are in the process of transforming themselves from publicly funded pilot projects into privately funded, self-sustaining programs. Whether or not watershed markets will be able to make this all-important leap depends, in large part, on how well watershed managers understand the science of the services they are selling. "The general perception is that deforestation leads to less water," says Meine van Noordwijk, hydrologist with Consultative Group on International Agricultural Research (CGIAR) in Bogor, Indonesia. But, he warns, it's not that simple.

Myth 1: Forests prevent floods

Unfortunately, the link between forests and flooding is a little understood matter of scale and, according to van Noordwijk, "What is wrong with the general dialogue is observations taken at one scale are assumed relevant at all scales." Hydrologist L.A. Bruijnzeel of Vrije Universiteit in Amsterdam has shown that, despite the research linking deforestation to local risks of flooding in smaller catchments, there is sparse evidence linking deforestation to flooding in larger watersheds. Most studies are conducted on watersheds smaller than 10 hectares, he observes, while policymakers are generally interested in scales of 100 hectares and up. Absent data, a blame game based on widespread myths is often played in the wake of disastrous flooding. "It's easier to put the blame sometimes far away rather than looking at your own system," says Thomas Hofer, UN Food and Agricultural Organization Forestry Officer. Motivated by consistent headlines blaming mountain people in the Himalayas for flooding in Bangladesh, Hofer recently conducted one of the only large-scale hydrological studies of watershed services in the world. And, perhaps not surprisingly, his findings were surprising. Specifically, Hofer discovered that the coincidental timing of the highest flow in the main rivers, rainfall peaks within Bangladesh, high groundwater levels, and runoff from the nearby Meghalaya Hills, drove floods in Bangladesh regardless of vegetation patterns. He concluded that afforestation programs in the mountains-while essential for mountain communities and their local environment – could not prevent floods in the lowlands. Other scientists, too, now agree that land use has no real impact in the face of extreme climate events. While good plant cover protects against surface erosion and well-developed tree cover may reduce shallow landslides, there's only so much trees can do in the face of prolonged periods of rain. Once the soil is saturated, larger slides are difficult to stop, forest or no.

Myth 2: Forests increase flows

Forests have long been described as a water-wicking sponge-absorbing intense rainfall during storms and then releasing water when it is most needed during drier times. But Ian Calder, hydrologist with the Centre for Land Use and Water Resources Research (CLUWRR) at Newcastle University, has found that reforestation efforts can actually lower flows. "In many cases the extra evaporation from a forest outweighs any small increase in rainfall such that the net effect is flow reduction," says Calder. "I believe you can ensure a good steady supply of water and more with a well-managed land use that has no forest. But well-managed is the important qualifier." As Calder suggests, watersheds are an intricate matrix of vegetation, soils, and underlying geology. Scientists now say that determining the effects of specific vegetation types within a watershed landscape is the single most urgent watershed research need. The emerging lesson from early research in this area, says Bruijnzeel, is that forest influences on rainfall patterns are highly site-specific. Evidence suggesting forests increase rainfall in some areas does exist, but they often have a smaller effect on precipitation patterns in maritime climates than, for instance, changing sea surface temperatures. Cloud mountain forests, meanwhile, tell a different story. Recent focus on cloud forest systems in Costa Rica shows that fewer clouds form over cleared areas, suggesting that large forests may affect rainfall patterns. "There's nothing fundamentally different between processes of a tropical or temperate forest, but in cloud mountain systems, cloud water may be sufficient to more than balance the extra interception loss expected from a forest, leading to net increase in flow from the forest," explains Calder. In lieu of site-specific data, researchers must be more creative with existing data. "Expressing flow relative to rainfall is essential," says van Noordwijk. He adds that metrics should be separated conceptually into 3 areas: rainfall variation, landscape make-up, and human activities. By pursuing this approach, he says, "We're starting to make progress."

Tool Time

Scientists are on the verge of moving beyond what forests do NOT do to what they DO, in fact, do in watersheds. "In the last 5-10 years, hydrologists have come up with general purpose adaptable models," says World Bank environmental economist Kenneth Chomitz. Using these innovative modeling techniques, scientists are now studying watershed services at the larger, landscape scales useful to policy-makers. And, as they look at the combined effects of forests and farms, researchers say they will, for the first time, be able to sort out the weaker effects of deforestation from the stronger effects of climate, geology and terrain. Existing models such as TOPOG, developed by scientists at Australia's Commonwealth Scientific and Industrial Research Organization (CSIRO) scientists, describe how water moves through landscapes; over the land surface, into the soil, through the soil and groundwater and back to the atmosphere via evaporation. Sediment transport can also be estimated. TOPOG, however, is not immune to the scale issues. It is intended for use with small catchments no bigger than 10 square kilometers. The simulation model GenRiver, meanwhile, allows scientists to explore historical changes in river flow resulting from land use change. And a new catchment climate classification tool -designed by CSIRO scientists with Bruijnzeel-models seasonal rainfall, land use, potential evapotranspiration, relief, soils and geology to identify opportunities for water resources services from afforestation that have been missed so far. While consensus is growing about the roles of watersheds, models can serve as a bridge between those who feel that processes are largely understood and applicable to every region, and those who believe much more site-specific data is needed to understand regional workings. But models still face stumbling blocks. Firstly, cost. Site-specific hydrological models in Monteverde, Costa Rica have taken 3 years and $800,000, and researchers are still working on answers. Models also tend to characterize land as pure forest or pure agriculture-hardly reflective of the mosaic of land uses found in areas such as Southeast Asia. And, last but not least, there is still a significant gap in knowledge of the time scale of degradation versus rehabilitation.

On Balance

Despite their limitations, scientists stress that models are advancing policy by replacing old assumptions about forests and hydrology with more targeted questions. According to Chomitz at the World Bank, "The nitty-gritty question that models and data are going to help us sort out is 'Is this action going to make a positive difference?'" As the yeas and nays to this query begin to roll in from around the world, a weighty new task is already forming on the horizon: sorting out the real opportunities for sustainable market-based conservation from the opportunities for a more traditional kind of government and non-profit support. For too long, people have perpetuated the myth that forests represent a magic remedy for watershed ills in order to help secure funding for vital community development and forestry schemes. Now, with policy-makers the world-over looking favorably on payments for environmental services, the time has come to go back and take a good look at the science, otherwise advocates of a market-based approach to watershed conservation risk blowing their repute by misdiagnosing the problem. And, in the case of watersheds, prescribing a good treatment to the wrong patients will advance neither markets nor the environment in the long-run. Virginia Gewin is a freelance science writer based in Portland. She may be reached at

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