Hydrologic Cycle
The continuous global movement and transformation of water through Earth's atmosphere, land surface, oceans, and subsurface aquifers.
Governing formula
Water Balance: P = E + R + ΔS (Precipitation = Evaporation + Runoff + Storage Change)
SI unit
Global Water Flux (km³/year)
In depth
Driven by solar energy and gravity. Water evaporates from oceans, transpires from vegetation, travels atmospherically, condenses into clouds, falls as precipitation, and returns to oceans via surface runoff and groundwater flow.
Examples in the real world
Evaporation from tropical oceans feeding global cloud systems and precipitation.