Ecosystem assessment (C2.04)


Healthy ecosystems provide a wide range of valuable goods and services to people. Sustainable management of riverine ecosystems and water flows has to take that into account during prioritisation, and needs to understand the effects that changing ecosystems have on human well-being. Ecosystem assessment is a tool for that. It analyses the effects of climate change, for example, on ecosystems and on their ability to provide people with the goods that they are used to. Thereby, it gives decision makers the information they need to improve the conservation and sustainable use of ecosystems and to minimize negative impacts of water use.

Riverine ecosystems include components like the source area, river channel, riparian zone, floodplain, ground water, wetlands and estuary, as well as any particularly important features such as rare and endangered species. A thorough ecosystem assessment needs to not only consider the effects of change on the ecosystem, but also on the people who depend on the services offered by the ecosystem and for whom a changed ecosystem can have a number of more or less dire consequences.

Ecosystem services are often grouped into four categories: provisioning, which addresses the production of food and water; regulating, which refers to the control of climate and disease; supporting, for nutrient cycles and crop pollination; and cultural, which includes spiritual and recreational benefits.

Key questions for ecosystem assessment include:

  • What is the state of the ecosystem right now? What is its spatial extent and condition?
  • What are the stressors and threats to the ecosystem?
  • Which kinds of services are provided and in which quality, quantity, and spatial distribution?
  • Who lives in the ecosystem and which services provided by the ecosystem do they use?
  • Which trends can be identified in the state of the ecosystem, its services, and uses over a recent or distant time scale?
  • How does/ did the ecosystem condition respond to change?

The concept of Environmental Flow describes the quantity, quality and timing of water flows required to sustain riverine ecosystems. It has emerged in relation to the Natural Flow Paradigm which suggests that the management of river flows should be undertaken in ways to mimic natural flows. The condition in which ecosystems and their services are sustained is essentially a socio-political decision: It may be set by international conventions (e.g. Ramsar Convention, Biodiversity Convention) and environmental flows must be allocated to maintain ecosystems in that desired condition. Alternatively, the environmental flows allocation is a negotiated trade-off between water users. In this case, the resulting ecosystem condition is determined by that negotiated and desired environmental flows allocation.

More than 200 different Environmental Flows Assessment (EFA) methodologies exist. In order to get the full picture that includes information on the uses of ecosystem services, a holistic, scenario-based approach should be chosen, using expert panel determinations and an effective user community participation procedure. EFA methodologies can be grouped into 4 different categories:

  • Hydrological Index methods, which are often referred to as desk-top or look-up table methods and rely primarily on historical flow records;
  • Hydraulic Rating Methods, which are based on historical flow records and use hydraulics as a surrogate for the biota (Wetted Perimeter Method);
  • Habitat simulation methodologies, which are based on hydrological, hydraulic, and biological response data;
  • Holistic methodologies, which explicitly adopt a comprehensive approach that factors in ecosystems and socio-economic considerations.

Lessons learned

  • Explicitly linking ecosystems to the provision of services, human well-being, and economic value is crucial to gain political as well as public support for allocation decisions taking into account environmental flows.
  • Ecosystem/Environmental Flows Assessments are most beneficial (and less costly) if undertaken in the early planning stages of a development project. Water resources managers, practitioners who conduct Environmental Impact Assessments (EIAs), and social scientists need to recognise the importance of downstream impacts of projects (including large-scale land-use changes) and include EFA into planning studies, EIAs and SEAs (see Tools C2.05; C2.03)
  • In basins where all water has been allocated to consumptive uses, it is very difficult/costly and often politically unacceptable to recover water for ecosystems. Therefore, it is important to protect/safeguard environmental flows in basins where water is still available (unallocated/unregulated). Further diversion of unregulated flows, from regulated or unregulated systems should only be allowed on the basis that ecological sustainability of riverine systems is not impaired.
  • The concept of early public participation should be endorsed and used in ecosystem assessment, to assess social and biophysical environmental impacts, and lead to the best resolution of problems.
  • Recognition of environmental flows in water resources policies and legislation (ideally with equal legal standing to other water users) provides an important impetus to include environmental flows in basin management plans; and thus provides important benchmarks for project-level decisions on water allocations.
  • Effective monitoring programmes based on ecological indicators are needed to demonstrate benefits of environmental flows allocations and allow for adaptive management.