Wetlands have historically been considered unproductive areas, gradually drained and reclaimed for human use, but with potentially large impact on carbon, water and nutrient cycles, as well as biodiversity. The global extent of wetland reclamation is unknown and important disagreements exist among current estimates. To reconcile these differences, we reconstructed the history of global wetland drainage over 1700-2000 by combining national statistics of drained area with maps of potential wetland cover and land use reconstructions. Wetland losses associated with seven drivers of loss were mapped globally: cropland, rice, forestry, peat extraction, urban area, pasture and wetland cultivation. We compared and combined the mapped cumulative wetland loss with regional-to-global data sources into a unified approach to estimating global wetland loss.
Results/Conclusions
We estimate that 2.1 million km2 of natural wetlands were drained or converted over this period, representing a loss of 14.3% (C.I. 11.1-27.4%) since 1700. Cropland expansion has been the most important driver of drainage, but forestry drainage and peat extraction were significant drivers in Northern Europe. This contrast with Asia and Africa where conversion to irrigated rice wetland cultivation dominated. Losses are concentrated in riparian corridors of the United States Midwest, central Asia and India as well as in Indonesian peatlands, while the vast northern peatlands are unmodified. Our estimate of global percentage loss suggests that previous estimates extrapolated from local records likely overstates wetland loss over the last centuries due to a geographic bias toward high-loss regions and susceptibility to a shifting baseline. Lower estimates of global loss should lessen the urgency to protect remaining wetlands in high-loss regions.