Global extent and distribution of wetlands: trends and issues

Abstract

Herein we review estimates of global and regional wetland area from ‘bottom-up’ approaches of site or national wetland inventories and ‘top-down’ approaches from global mapping and remote sensing. The trend for increasing wetland extent reported in the literature over time is a consequence of improved mapping technologies and methods rather than a real increase in wetland area, because a continuing trend for natural wetland loss and conversion is documented over the same time period. The most recent high-resolution estimate of global wetland area is in excess of 12.1×106km2, of which 54% is permanently inundated and 46% is temporarily inundated. Globally, 92.8% of continental wetland area is inland and only 7.2% is coastal. Regionally, the largest wetland areas are in Asia (31.8%), North America (27.1%) and Latin America and the Caribbean (Neotropics; 15.8%), with smaller areas in Europe (12.5%), Africa (9.9%) and Oceania (2.9%). It is likely that estimates of global wetland area published to date persist in underestimating the true wetland area. The ‘grand challenge’ of a global inventory integrating all types of permanent and temporary wetlands at high spatial resolution has yet to be fully achieved.

Significant feedbacks of wetland methane release on climate change and the causes of their uncertainty

“…The wetland fraction simulated by JULES compares well spatially (figure 1) and temporally (figure S2) with the SWAMPS-GLWD (Poulter et al 2017) observation-based product, and is within observational spread for global total wetland area (figure 1(e), Davidson et al 2018). A detailed assessment of simulated wetland uncertainty and its impact on the magnitude of wetland CH 4 feedback on climate change is provided in the supplementary material SI sections S1 and S7.…”

Quantifying how changing mangrove cover affects ecosystem carbon storage in coastal wetlands

“…For example, global changes are driving encroachment of woody species into grasslands and herbaceous marshes. Mangrove trees are woody species that dominate coastal wetlands of the tropics, and as extreme cold events become less frequent, mangroves are expanding to higher latitudes and increasing coverage at poleward range limits (Cavanaugh et al 2014, despite human activities driving declines in mangroves globally (Davidson et al 2018). Mangrove trees are woody species that dominate coastal wetlands of the tropics, and as extreme cold events become less frequent, mangroves are expanding to higher latitudes and increasing coverage at poleward range limits (Cavanaugh et al 2014, despite human activities driving declines in mangroves globally (Davidson et al 2018).…”

“…This is a widespread phenomenon, and such shifts in dominant species can alter microclimate, organic-matter sources, and biogeochemistry (Van Auken 2000, D'Odorico et al 2013, Guo et al 2017. Mangrove trees are woody species that dominate coastal wetlands of the tropics, and as extreme cold events become less frequent, mangroves are expanding to higher latitudes and increasing coverage at poleward range limits (Cavanaugh et al 2014, despite human activities driving declines in mangroves globally (Davidson et al 2018).…”

Wetlands In a Changing Climate: Science, Policy and Management

“…If a goal is to increase the amount CO 2 sequestrated by wetlands, it is worth considering how much wetland restoration or creation would be needed to make a significant difference. The annual amount of CO 2 sequestered by wetlands can be estimated using the data provided by Bridgham et al (2006) for the annual average rate of C sequestration by wetlands (~23 gCm -2 y -1 ), and the most recent estimate of the global wetland area (12,100,000 km 2 ) provided by Davidson et al (2017). Using these values, the annual amount of CO 2 sequestrated is equivalent to 278 TgCy -1…”