This study attempts to create regional divisions for environmental flow assessment based on net primary productivity (NPP). First, the world is categorized into six hydro-climatic regions according to seasonal flow variability and average monthly temperature. Second, a trophic level index is built in order to describe the potential richness of ecological structures of river channel. This model describes biomass flux in the river channel and rate of dependency on upper reaches. In poor productive areas such as desert or high latitudes biomass supplied from upper reaches contributes to sustain ecological richness. The hydro-climatic regions and the trophic levels highlight the regional characteristics of riverine ecosystems and indicate the priorities for setting the environmental flow objectives.
