Intra-year distribution of water discharge in global rivers

Intensive human interference, climate variability, and ongoing climate change affect the seasonality of runoff processes in rivers worldwide, which in turn may promote more frequent extreme flow events and cause irreversible damage to the ecological environment. Here we examine the global trend of the intra-year distribution of the seaward water discharge in 314 independent river basins, the total drainage area of which accounts for 2/3 of the total Earth land. The results show that the intra-year distribution of water discharge is homogenized between dry and flood seasons in 181 river basins, such as the Nile, Mississippi, Yangtze, Ganges, etc., but polarized in 39 basins, e.g. Amazon, Zaire, and Niger. Considering the primary factors affecting the intra-year distribution of water discharge, i.e. precipitation (P), evaporation (E), glacial runoff (G), and dam operations (D), the global river basins can be divided into GDEP, DEP, GEP, and EP types. Using the stepwise regression method, quantitative contributions of each factors to either homogenization or polarization phenomena are calculated. It is found that the homogenization of water discharge is mainly controlled by dam operations in GDEP and DEP river basins, but dominated by the homogenized precipitation in GEP and EP river basins. Homogenized evaporation and polarized precipitation are the major factors behind the polarization of water discharge. This work is of importance to flood/drought disasters control and sustainable riverine/coastal eco-system management.