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