Paris, 9 May 2012
Marshes, lagoons, swamps and bogs are all types of wetlands—regions where water is the main controlling factor for the environment and its plant and animal life. Although they cover less than 5% of the Earth's land surface, these areas play a key role in human activities, biodiversity, climate and the water cycle. Indeed, they produce one third of atmospheric methane, a major greenhouse gas. Moreover, these regions impact the transfer of continental freshwater to the sea and alter local weather by enhancing evaporation.
A better understanding of wetlands, their way of functioning and their variability and dynamics over time, are essential for assessing climate change and making sound recommendations for water resource management. Characterizing wetland distribution and quantifying seasonal and inter-annual variations across the globe is, however, a huge challenge. No similar study had ever been undertaken until now, as these areas are diverse and spread across the whole planet from the tropics to the Arctic.
By combining and simultaneously analyzing a large amount of data from different satellites, the researchers succeeded in developing the first mapping of wetlands and their temporal dynamics throughout the world over fifteen years. The first conclusion from this study is that the extent of wetlands varied greatly during any year, but also from one year to another, with strong modulation during El Niño events. Moreover, between 1993 and 2007, scientists observed a 6% fall in wetland areas. This trend was particularly severe in tropical and subtropical regions. The highest declines are concentrated in the areas where the largest increases in human population have been recorded over the last two decades.
This study suggests that population pressure impacts hydrological cycles at the global scale. This pressure may stem from the draining of wetlands for urban development and the increase in water extraction from wetlands.
© Fabrice Papa
Areas of the world covered by wetlands. Data shown is the annual average for the period between 1993 and 2007, estimated from satellite data (areas are given in km2; each pixel represents 773km2).
1 - Estellus finds applications for CNRS research results. The company is specialized in the treatment and exploitation of satellite data in the environment and earth sciences fields. See View web site
Changes in land surface water dynamics since the 1990s and relation to population pressure, Prigent, C., F. Papa, F. Aires, C. Jiménez, W. B. Rossow, and E. Matthews, Geophys. Res. Lett., doi:10.1029/2012GL051276, in press (2012).
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