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Wetland Extent Trends Index

Key indicator facts

Indicator type

State

Applicable for national use

No

Indicator classification

Operational and included in the CBD's list of indicators

Indicator type

State

Applicable for national use

No

Indicator classification

Operational and included in the CBD's list of indicators

Last update

2014

Coverage

Global

Availability

Not freely available

Partners

Ramsar.logo

Ramsar Convention on Wetlands

Unep wcmc

UNEP-WCMC

Contact point

Indicator description

The Wetland Extent Trends Index measures trends in wetland area over time, enabling the rate of loss (or growth) of wetland areas to be estimated and giving an indication of the status of wetlands globally. The analysis is based on a database containing over 1,000 wetland extent time-series’ and a methodology was developed to identify and account for thematic and geographic gaps, and conversely, over-representation in the data.

Related Aichi Targets

Primary target

5

Target 5:

By 2020, the rate of loss of all natural habitats, including forests, is at least halved and where feasible brought close to zero, and degradation and fragmentation is significantly reduced.

Secondary targets

Target 14:

By 2020, ecosystems that provide essential services, including services related to water, and contribute to health, livelihoods and well-being, are restored and safeguarded, taking into account the needs of women, indigenous and local communities, and the poor and vulnerable.

Primary target

5

Target 5:

By 2020, the rate of loss of all natural habitats, including forests, is at least halved and where feasible brought close to zero, and degradation and fragmentation is significantly reduced.

5
14

Related SDGs

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GOAL 6 - Ensure availability and sustainable management of water and sanitation for all.

Target 6.6| Official indicator

By 2020, protect and restore water-related ecosystems, including mountains, forests, wetlands, rivers, aquifers and lakes

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GOAL 6 - Ensure availability and sustainable management of water and sanitation for all.

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Other related MEAs and processes

Cites high resolution

CITES

Target 1.6| Relevant indicator

Parties cooperate in managing shared wildlife resources.

Cms logo blue4c

CMS

Target 10| Relevant indicator

All key habitats and sites for migratory species are identified and included in area-based conservation measures so as to maintain their quality, integrity, resilience and functioning in accordance with the implementation of Aichi Target 11.

Target 11| Relevant indicator

Migratory species and their habitats which provide important ecosystem services are maintained at or restored to favourable conservation status, taking into account the needs of women, indigenous and local communities , and the poor and vulnerable.

Indicator icon

IPBES Global Assessment Chapters

Chapter 2| Official indicator

Status and trends; indirect and direct drivers of change

Indicator icon

IPBES Regional Assessment Chapters

Chapter 2| Official indicator

Nature’s benefits to people and quality of life

Chapter 3| Official indicator

Status, trends and future dynamics of biodiversity and ecosystems underpinning nature’s benefits to people

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Ramsar

Target 6| Relevant indicator

There is a significant increase in area, numbers and ecological connectivity in the Ramsar Site network in particular under-represented types of wetlands including in under-represented ecoregions and transboundary sites

Target 12| Relevant indicator

Restoration is in progress in degraded wetlands, with priority to wetlands that are relevant for biodiversity conservation, disaster risk reduction, livelihoods and/or climate change mitigation and adaptation

Cites high resolution

CITES

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CMS

Indicator icon

IPBES Global Assessment Chapters

Indicator icon

IPBES Regional Assessment Chapters

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Ramsar

Cites high resolution
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Indicator icon
Ramsar.logo

Themes

Marine

Marine & freshwater habitats

View related indicators >
Marine

Partners

Ramsar.logo
Unep wcmc

Key indicator facts

Indicator type

State

Applicable for national use

No

Indicator classification

Operational and included in the CBD's list of indicators

Indicator type

State

Applicable for national use

No

Indicator classification

Operational and included in the CBD's list of indicators

Last update

2014

Coverage

Global

Availability

Not freely available

Indicator description

The Wetland Extent Trends Index measures trends in wetland area over time, enabling the rate of loss (or growth) of wetland areas to be estimated and giving an indication of the status of wetlands globally. The analysis is based on a database containing over 1,000 wetland extent time-series’ and a methodology was developed to identify and account for thematic and geographic gaps, and conversely, over-representation in the data.

Contact point

Graphs / Diagrams


Figure 1. Global average marine/coastal and inland wetland extent trends relative to extent in 1970 and up until 2008. 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 the gains and declines cancel each other out.

Current storyline

The indices show the average trend in wetland extent change relative to 1970, which is given a value of 1. A decrease in the index means that wetland extent has declined on average, which could be due to conversion to another wetland type or conversion to a non-wetland state. A constant index represents no overall change in wetland extent, or that the gains and declines over the assessed period cancel each other out.

Results for the average trends in each of the two wetland types are shown above in Figure 1. This shows that, on average, inland and marine/coastal wetlands have declined over the 38 year period, by approximately 30 %. Human-made wetlands were excluded from this analysis but could be included in future. These are average trends – the relative rates of declines of classes within the wetland types (e.g. intertidal wetlands and lagoons) vary in magnitude.

As conversion of wetland to non-wetland (wetland ‘loss’) was not discriminated from conversion of one form of wetland to another during data collection due to time constraints, there is currently insufficient information in the database to associate the rise in human-made wetlands with conversion from natural wetland, although this is a possible scenario. Some data sources did contain this information and with further work the discrimination would be possible. Individual graphs of the three wetland types with plotted confidence intervals can be found in supplementary

Technical notes Appendix 5. Note that there has been no weighting applied to these preliminary wetland type indices due to a lack of knowledge of the global distribution of specific wetland classes.

Data and methodology

Coverage: Global.

Scale: Data is gathered from sources in literature. In total, 1100 time-series from 170 source references were used in the wetland extent database.

Time series available: 1970-2008.

Next planned update: 2016.

Possible disaggregations: The WET Index can be disaggregated for some regions.

Metadata: The data sources used a variety of methods to measure change in wetland area. Over half used Landsat images including MultiSpectral Scanner (MSS), Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM+) satellite images, while other used aerial photographs and historical maps. Many sources used a mixture of methods in order to gather sufficient information to establish a trend and each method will have strengths and weaknesses. For example, while satellite imagery has advantages for assessing remote wetlands or those that would otherwise by prohibitively expensive to assess in the field, a major limitation is that infrequent imagery will fail to capture natural fluctuations in their area (Davidson and Finlayson, 2007). In order to maximise the volume of data used to calculate the WET index, no further judgement of quality was taken beyond filtering the data for extreme annual rates of change.

Methodology: Wetland extent change time-series data from 170 source references were entered into a database. Each record was tagged with its Ramsar region (Africa, Asia, Europe, North America, Neotropics and Oceania), subregion, wetland characteristic data (e.g., wetland type: marine/coastal, inland or human-made) and source reference. Full details of the database construction including an explanation of what constitutes each wetland type can be seen in the paper Dixon et al. (2016).

A methodology was developed to account for geographical and thematic biases in time series. Data on individual wetlands trends were first sorted into the six Ramsar regions and three Ramsar wetland types, making 18 groups. To account for geographical unevenesss, the data were then further subdivided into 126 subregions and 20 wetland classes (i.e. sub-types), making a matrix of 2,520 possible combinations. The average trend in wetland extent was then calculated for all wetlands in each cell of the matrix for which one or more time-series were available, making 1,100 average trends in total (1,420 cells had no data).

To generate the indices, the average trends for individual subregion-wetland class combinations (matrix cells) were then aggregated, giving each cell equal weight, and analysed using the Living Planet Index methodology (Collen et al., 2009; Loh et al., 2005). The analysis was run from 1970 to 2008 because the amount of data available decreased sharply either side of that time period. The index therefore does not show the change in wetland extent that happened before 1970, which was extensive in some regions such as Europe where there is a long history of wetland drainage.

The indices were not weighted due to a lack of knowledge on the extent of specific wetland classes within regions.

National use of indicator

The WET index is currently calculated for the Ramsar regions. There remains a great deal of geographic unevenness in the data coverage and therefore bias within regions, as well as between regions. And there are significant regional data gaps. For example, it was not possible to calculate a regional index for the Neotropics, which is recognised as being data poor for wetland extent data (Davidson, 2014; Finlayson and Spiers, 1999). As a result, wetlands in the Neotropics are not currently represented in the global WET index. Efforts to fill such gaps can be made in the future by reviewing non-English scientific literature, administrative and NGO reports as well as collaborating with regional experts. Improvement to the WET index will rely on future expansion of the database to fill these gaps. As such, it is not currently possible to disaggregate the WET Index to the national level. However, the methodology has potential for national level application.

Further resources

Key indicator facts

Indicator type

State

Applicable for national use

No

Indicator classification

Operational and included in the CBD's list of indicators

Indicator type

State

Applicable for national use

No

Indicator classification

Operational and included in the CBD's list of indicators

Last update

2014

Coverage

Global

Availability

Not freely available

Partners

Ramsar.logo

Ramsar Convention on Wetlands

Unep wcmc

UNEP-WCMC

Contact point