Definition
The continuous movement of water between the Earth's surface and the atmosphere through evaporation, condensation, and precipitation. Water evaporates from oceans, lakes, and land into the atmosphere as water vapor, condenses into clouds, falls back to the surface as rain or snow, and eventually returns to the bodies of water where the process began.
Plain English
The endless loop of water rising into the air, forming clouds, falling back as rain or snow, and rising again.
Context Anchor
Seen in aviation weather study when learning how moisture in the atmosphere leads to clouds, rain, snow, fog, and other weather that affects flying.
Derivation
From the Greek hydro (water) and logos (study of). The word hydrological refers to anything having to do with the movement and behavior of water. Cycle comes from the Greek kyklos meaning 'circle' -- pointing to the fact that water keeps returning to where it started.
Why Pilots Care
Knowledge of this cycle aids in anticipating weather hazards such as fog, rain, and thunderstorms that can affect visibility, aircraft performance, and landing conditions.
Grounding Statement
Picture water rising invisibly off a warm lake on a summer morning, gathering into clouds overhead, falling as an afternoon rain shower, and running back into the same lake -- that's one turn of the cycle.
Intuition Check
Do not think of the hydrological cycle as only “rain.” Rain is just one part of the larger water loop between the ground and the air.
Example Sentence 1
The instructor explained that thunderstorms, fog, and icing are all visible stages of the hydrological cycle.
Example Sentence 2
Understanding the hydrological cycle helped the student pilot recognize why cumulus clouds form after daytime heating.