(Phys.org) -- The area of the globe covered by wetlands (swamps, marshes, lakes, etc.) has dropped by 6% in fifteen years. This decline is particularly severe in tropical and subtropical regions, and in areas that have experienced the largest increases in population in recent decades. These are the conclusions of a study conducted by CNRS and IRD researchers from the Laboratoire d'étude du rayonnement et de la matière en astrophysique, Laboratoire d'études en géophysique et oceanography spatiales and the start-up Estellus. To obtain these results, the scientists performed the first worldwide mapping of the wetlands and their temporal dynamics, for the years 1993 to 2007. This study, which has just been published in the journal Geophysical Research Letters, emphasizes the impact of population pressure on water cycles.