RHMS is a new rainfall runoff model to simulate hydrological problems. The advantage of this platform is, the quick and easy integration with R diverse ecosystem. For instance, coupling a rainfallrunoff model like HEC-HMS with a precipitation data generator or a complex statistical procedure might be a quite challenging task. However, availability of statistical and modeling techniques in R makes the connection of hydrological processes (implemented in this package) with such techniques quite straightforward. The package is capable to model semi-distributed basins and can calibrate (sub)basins’ physical parameters using optimization.