The given diagram demonstrates the hydrologic cycle, from above and below the surface of the Earth.
Overall, this natural process consists of 7 main steps. Those steps can be divided into 3 main stages, ranging from the evaporation of ocean water and the formation of clouds to the conveyance of water to the sea.
Regarding the evaporation stage, the ocean water is vaporised by the heat from the sun, which then condenses into clouds. Subsequently, these clouds are carried by wind to higher altitudes, preparing them for the precipitation stage. Afterwards, water from the rain in higher lands will descend along the mountain road, combining with groundwater and going down to the impervious layer of the ground.
Simultaneously, the rainwater from lakes in the lower lands percolates into the soil and converges with the water stream in the higher altitudes as mentioned. This stream will then meet saltwater intrusion before moving to the ocean, restarting the process.