A new approach to costing ecosystem services

We know that despite their importance for local human well-being and regulation of ecosystem services, wetland integrity continues to decline. How can policies at the local, regional and global scale be better aligned? This is the question that the FORUM Wetlands for livelihoods is trying to answer this week in Kigali, Rwanda.

IWMI research is helping decision-makers to understand the impacts of wetlands and other ecosystems on the hydrological cycle.

Some wetlands store and clean water. Some floodplains buffer floods. Some mangroves and coral reefs protect coastal communities from storm surges. Without doubt the earth’s ecosystems play a crucial part in the hydrological cycle; in many cases through the regulation of flows.  Consequently it is not surprising that increasingly scientists and conservationists are arguing that the services provided by ecosystems should be considered much more in decision-making related to water infrastructure.

Photo credit: Harvey Barrison

However, the way ecosystems interact with the hydrological cycle is very complex: the result of a myriad of dynamic, interlinked processes, which are still poorly understood. The absence of both quantifiable data and a recognized method to include natural ecosystems makes it hard for water resource planners and managers to integrate them into decision-making and planning.


Seeking evidence of flow regulating functions

A new research report, Evaluating the flow regulating functions of natural ecosystems in the Zambezi River Basin, published by the International Water Management Institute (IWMI), in conjunction with the United Nations Environment Program (UNEP), addresses this issue. The authors sought evidence of the flow regulating functions of major ecosystems in the Zambezi River Basin and developed a simple, pragmatic approach to measure their impact on flows.

“To be able to include the flow regulating effects of natural ecosystems in decision-making, a method is needed that determines the differences in the flow regime in the presence and absence of an ecosystem”, explained IWMI Principal Researcher Matthew McCartney.

The method, which the researchers developed, is based on observed stream flow records. It is a straightforward approach that enables the simulation of the flows that would have occurred downstream of an ecosystem, as if that ecosystem was not present. The “with” (i.e. observed) and “without” (i.e. simulated) ecosystem flows can then be compared.  Standard hydrological methods can then be used to quantify the impact of the ecosystem on flood and low flows.


No simple relationships

In the Zambezi, the researchers’ findings were generally consistent with past research.  They showed that broadly floodplains decrease floods and increase low flows and headwater wetlands increase floods and decrease low flows. Forest, when covering more than 70% of the catchment, was found to decrease both flood flows and low flows. However, in all cases there were examples where specific ecosystems, affected flows in an unexpected way.  Simple relationships between the areal extent of a particular ecosystem and the impact on the flow regime were not found. This indicates that effects on flow are a function not just of the presence or absence of different ecosystem types, but are the outcome of a range of interacting factors, including topography, climate, soil, vegetation and geology.

“The method is not as sophisticated as hydrological modeling and has scope for improvement”, says McCartney. “But the strength of the method is that the impacts of natural ecosystems on flow are determined without the need for a complex computer model, which, in many cases, is based on assumptions about how different ecosystems function.  By using this method water resource planners and managers can understand the impacts of natural ecosystems and assess implications for communities living downstream. This way it is contributing to better incorporation of natural ecosystems into water planning and management.”

McCartney, M.; Cai, X.; Smakhtin, V. 2013. Evaluating the flow regulating functions of natural ecosystems in the Zambezi River Basin. Colombo, Sri Lanka: International Water Management Institute (IWMI). 59p. (IWMI Research Report 148). doi:10.5337/2013.206

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About the author:

Anna Deinhard is a Communications Fellow at the International Water Management Institute (IWMI). She has an MSc in Environmental Sciences from Linkoping University, Sweden, specialized in water and development.