A global map of mean annual runoff based on discharge observations from large catchments

This report describes the development of a global map of mean annual runoff (MAR) based on discharge observations from 1651 large catchments (10,003 to 4,691,000 km²) around the globe. The map was produced based on the assumption that the mean annual volumetric discharge difference between a station and its upstream neighbor(s) represents the MAR generated in the interstation region. The produced map represents a unique spatial estimate of MAR at a global scale useful for, among other things, the spatial evaluation of macro-scale hydrological models. Compared to an equivalent map developed at the University of New Hampshire, the new map (i) is based on substantially more catchments (1651 versus 663), (ii) has a higher resolution (∼0.04° versus 0.5°), (iii) covers a larger portion of the hydrologically-active, ice-free land surface (58.9 % versus 56.5 %), and (iv) agrees considerably better with a completely independent MAR map based on small catchments.