The global extent of natural wetland declined by 30 per cent between 1970 and 2008, according to new research led by UNEP-WCMC for the Ramsar Convention Secretariat.

The Wetland Extent Trends (WET) index, which revealed the 30 per cent decline, is the world’s first indicator of change in area of natural wetland worldwide. It fills an important gap in the suite of global biodiversity indicators that enable progress towards international environmental targets to be tracked.

“For the first time, we have a method for assessing the changing extent of natural wetlands,” said Matthew Dixon, who created the WET database at UNEP-WCMC. “The WET index is already proving useful for evaluating progress on wetland-related policy objectives including those adopted under the Ramsar Convention and the Convention on Biological Diversity.”

Based on the Living Planet Index, which is used to measure global trends in wild vertebrate species abundance, the WET index compiles time-series records from studies all over the world to assess changes in the extent of natural wetlands at a global and sub-global scale. Currently drawing on over 1,000 different time-series records, the WET index makes use of both ground-based and remotely sensed data and can be updated as more records become available.

The results of the WET index show that marine and coastal wetlands are declining more quickly than inland wetlands. Regional differences can also be identified by the WET index, with figures varying from about 50 per cent in Europe to about 17 per cent in Oceania.

Wetland ecosystems are rich in biodiversity and valuable for the services they provide to people, such as water security, erosion control and support to a range of production sectors including agriculture. Their loss has negative impacts on human well-being. The threats to wetlands are numerous and include pollution, fragmentation and transformation, all of which lead to degradation and loss of extent.

“Given their importance for water security, food security and human health, an indicator tracking change in wetland extent could have an important role as an indicator for the recently adopted Sustainable Development Goals,” said Matt Walpole, Director of Partnerships and Development at UNEP-WCMC and leader of the study. “As the WET index is straightforward and relatively cost-effective to maintain and update, it is capable of providing an ongoing picture of how natural wetlands in different parts of the world are changing.”

Now that the methodology for the WET index has been established, the next step will be to expand the WET database to fill gaps in coverage and to make it useful for national as well as international purposes. It could also have wider application beyond wetlands.

“Ecosystem change indicators for use in international policy processes are relatively rare”, added Matt Walpole. “The WET index offers a proof-of-concept for a method that could be used to create extent indicators for other ecosystems with incomplete data.”

The WET index is published online in the journal Biological Conservation.

The global Natural WET index and the disaggregated Inland and Marine/coastal WET indices with 95% confidence intervals. A decrease in the index means that wetland extent has declined on average, while a constant index represents no overall change in wetland extent or that gains and declines cancel each other out.

Publication information

M.J.R. Dixon, J. Loh, N.C. Davidson, C. Beltrame, R. Freeman, M. Walpole. Tracking global change in ecosystem area: The Wetland Extent Trends index. Biological Conservation, Volume 193, January 2016, Pages 27–35.