How is systems theory approach applied to the hydrological cycle?

The hydrological cycle can be understood through a systems approach. Systems are bounded and have inputs, outputs and throughputs. The global hydrological cycle is a closed system driven by solar energy and gravitational potential energy. The throughputs are mediated by processes internal to the system which are often understood grounded together as sub-systems. For instance, we might consider a drainage basin sub-system which has inputs of rainfall from the atmosphere, outputs of river discharge (to the ocean) and evaporation (to the atmosphere).