PhysicsChapter 10: Earth's Climate
The Hydrosphere and Water Balance
The hydrosphere is all water on Earth — liquid, ice, and vapour.
Learning objectives
- Explain The Hydrosphere And Water Balance in easy language and identify its main physical principle.
- Apply the key relation or evidence for The Hydrosphere And Water Balance to a Class 12 conceptual or numerical question.
- Present an FBISE-style answer with correct reasoning, symbols, units, and a clear final statement.
Definition
The hydrosphere is all water on Earth — liquid, ice, and vapour. Oceans cover ~70% of the surface and help regulate climate by moving heat and moisture. The hydrological cycle redistributes water via evaporation, condensation, precipitation, runoff, and infiltration. Water-balance equation (book): ΔS = P − E − Q, where ΔS is change in storage, P precipitation, E evapotranspiration, Q runoff. Volumes = depth × area when converting mm over a watershed to m³.
Mathematical form
S = P
P = ΔS + E + Q. Keep mm consistent before co
Where / symbols
- THE HYDROSPHERE AND WATER BALANCE
- The hydrosphere is all water on Earth — liquid, ice, and vapour.
- CYCLE PIECES
- Sun drives evaporation; condensation forms clouds; precipitation returns water; runoff and infiltration move it on/under land; transpiration from plants.
- STORAGE NUMERICS
- Convert mm → m and km² → m².
Relationship
- ΔS = P − E − Q
Overview
Cycle, then calculation:
Cycle Pieces
Sun drives evaporation; condensation forms clouds; precipitation returns water; runoff and infiltration move it on/under land; transpiration from plants.
Examples Figure labels · Pakistan monsoon context named later · Educational only
Storage Numerics
Convert mm → m and km² → m². Volume = depth × area. Then ΔSv = Pv − Ev − Qv. Or rearrange for missing depth.
Examples Example: A=120 km², P=110 mm… → ΔS_v = 2.4×10^6 m³ · Assignment: find P from ΔS, E, Q · Show conversions
Overview — The Hydrosphere And Water Balance
The hydrosphere is all water on Earth — liquid, ice, and vapour. Oceans cover ~70% of the surface and help regulate climate by moving heat and moisture. The hydrological cycle redistributes water via evaporation, condensation, precipitation, runoff, and infiltration. Water-balance equation (book): ΔS = P − E − Q, where ΔS is change in storage, P precipitation, E evapotranspiration, Q runoff. Volumes = depth × area when converting mm over a watershed to m³.
Cycle Pieces
Sun drives evaporation; condensation forms clouds; precipitation returns water; runoff and infiltration move it on/under land; transpiration from plants. Examples: Figure labels; Pakistan monsoon context named later; Educational only.
Storage Numerics
Convert mm → m and km² → m². Volume = depth × area. Then ΔSv = Pv − Ev − Qv. Or rearrange for missing depth. Examples: Example: A=120 km², P=110 mm… → ΔS_v = 2.4×10^6 m³; Assignment: find P from ΔS, E, Q; Show conversions.
Worked or exam application
If ΔS, E, Q given as depths: P = ΔS + E + Q. Keep mm consistent before converting.
Explanation
If ΔS, E, Q given as depths: P = ΔS + E + Q. Keep mm consistent before converting.
In simple words
Evapotranspiration = evaporation + plant transpiration.
Key points
- ΔS = P − E − Q
- oceans store heat
- cycle redistributes
- P · E · Q named
- soil water
Exam preparation
Exam Focus
Quick revision
Revision Zone
Review the key facts, formulas and checks before you move on.The Hydrosphere and Water Balance
Sticky Notes · Quick Revision
Core Idea
- The hydrosphere is all water on Earth — liquid, ice, and vapour.
- Oceans cover ~70% of the surface and help regulate climate by moving heat and moisture.
Cycle Pieces
- Sun drives evaporation; condensation forms clouds; precipitation returns water; runoff and infiltration move it on/under land; transpiration from plants.
Storage Numerics
- Convert mm → m and km² → m².
- Volume = depth × area.
Apply It
- If ΔS, E, Q given as depths: P = ΔS + E + Q.
- Keep mm consistent before converting.
Common Error
- Evapotranspiration = evaporation + plant transpiration.
- Do not quote a formula for The Hydrosphere And Water Balance without defining its symbols, using SI units, and stating any required condition.
- Do not mix up Cycle Pieces and Storage Numerics; compare their roles before answering.
FBISE Exam Check
- Define The Hydrosphere And Water Balance before using it.
- Show the physics in logical steps and define every symbol.
- Use correct units, signs, directions, and assumptions.
60-second revision
- The hydrosphere is all water on Earth — liquid, ice, and vapour.
- Cycle Pieces: Sun drives evaporation; condensation forms clouds; precipitation returns water; runoff and infiltration move it on/under land; transpiration from plants.
- Storage Numerics: Convert mm → m and km² → m².
- Exam reminder: Evapotranspiration = evaporation + plant transpiration.
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