摘要：Abstract. Many maps of open water and wetlands have been developed based on three mainmethods: (i) compiling national and regional wetland surveys,(ii) identifying inundated areas via satellite imagery and (iii) delineatingwetlands as shallow water table areas based on groundwater modeling. However,the resulting global wetland extents vary from 3 % to 21 % of theland surface area because of inconsistencies in wetland definitions andlimitations in observation or modeling systems. To reconcile thesedifferences, we propose composite wetland (CW) maps, combining two classes ofwetlands: (1) regularly flooded wetlands (RFWs) obtained by overlappingselected open-water and inundation datasets; and (2) groundwater-drivenwetlands (GDWs) derived from groundwater modeling (either direct orsimplified using several variants of the topographic index). Wetlands arestatically defined as areas with persistent near-saturated soil surfacesbecause of regular flooding or shallow groundwater, disregarding most humanalterations (potential wetlands). Seven CW maps were generated at 15 arcsecresolution (ca. 500 m at the Equator) using geographic information system(GIS) tools and by combining one RFW and different GDW maps. To validate thisapproach, these CW maps were compared with existing wetland datasets at theglobal and regional scales. The spatial patterns were decently captured, butthe wetland extents were difficult to assess compared to the dispersion ofthe validation datasets. Compared with the only regional dataset encompassingboth GDWs and RFWs, over France, the CW maps performed well and better thanall other considered global wetland datasets. Two CW maps, showing the bestoverall match with the available evaluation datasets, were eventuallyselected. These maps provided global wetland extents of 27.5 and29 million km2, i.e., 21.1 % and 21.6 % of the global land area,which are among the highest values in the literature and are in line withrecent estimates also recognizing the contribution of GDWs. This wetlandclass covers 15 % of the global land area compared with 9.7 % for RFW(with an overlap of ca. 3.4 %), including wetlands under canopy and/orcloud cover, leading to high wetland densities in the tropics and smallscattered wetlands that cover less than 5 % of land but are highlyimportant for hydrological and ecological functioning in temperate to aridareas. By distinguishing the RFWs and GDWs based globally on uniformprinciples, the proposed dataset might be useful for large-scale land surfacemodeling (hydrological, ecological and biogeochemical modeling) andenvironmental planning. The dataset consisting of the two selected CW mapsand the contributing GDW and RFW maps is available from PANGAEA athttps://doi.org/10.1594/PANGAEA.892657 (Tootchi et al., 2018).
