Moisture: Hydrologic Cycle

Key Topics

• Hydrologic cycle components
• Condensation, evaporation, and precipitation
• Water movement in the atmosphere
• Importance of atmospheric water

Overview of the Hydrologic Cycle

• Most water on Earth is in the oceans (96.5%-97.2%).
• Freshwater is 2.8% of total water; much of it is in ice and glaciers.
• Atmospheric water is a small but crucial part of the water cycle.

Importance of Precipitation

• Precipitation: liquid/solid water falling from the atmosphere.
• Essential for human life and ecosystems.

State Changes and Energy

• Water State Changes:
  • Solid (ice) to liquid
  • Liquid to gas (evaporation)

Energy Calculations (Sample Problem)

• To move 10 grams of ice from -2°C to 120°C:
  • Use specific heat formula:
    • grams of ice × specific heat × temperature change
• Energy stages:
  • Ice to liquid: 0.5 calories/gram
  • Liquid water: 1 calorie/gram
  • Boiling point (100°C): 80 calories/gram to evaporate
  • Evaporation: 590 calories/gram

Evaporation Energy

• Evaporation: movement of water from surfaces to the atmosphere.
• Takes 80% of absorbed solar radiation.

Condensation

• Cooling causes water vapor to turn back into liquid (or ice).
• Releases energy back into the atmosphere.

Processes: Evaporation and Transpiration

• Evaporation: Water moving from saturated surfaces to the atmosphere.
• Transpiration: Water released by plants during photosynthesis.
• Evapotranspiration: Combined effect.

Influencing Factors for Evapotranspiration

• Availability of water: 85% from oceans, 15% from land.
• Temperature: Higher temperatures lead to more evaporation.
• Humidity: High humidity lowers evaporation.
• Wind: Increases evaporation by moving water molecules.
  • Practical examples: drying clothes, hair dryers, car dryers.

Potential vs. Actual Evapotranspiration

• Potential Evapotranspiration (PET): Evaporation with unlimited water.
• Actual Evapotranspiration (AET): Evaporation with real-world water availability.
• Deficits: When PET > precipitation.

Measuring Evapotranspiration

• Evaporation pans and soil columns.

Water Budgets and Climate

• Climatic Influence: Southeastern US (more evapotranspiration); Western US (mountain ranges).
• 100th Meridian: Historical threshold for rainfall patterns in the US.
• Water Surpluses/Deficits: Influence availability of rivers and lakes.

Groundwater and Human Use

• Groundwater recharge requires more infiltration than evapotranspiration.
• Importance for drinking water and reservoirs (e.g., Texas).

Applied Climate Examples

• Kingsport, Tennessee: Surplus most of the year, small summer deficits.
• Phoenix, Arizona: High evapotranspiration, significant water deficits.
• Ottawa, Canada: Comparable to Kingsport, but in a cooler climate.

Wrap-Up

• Remember the water cycle components and their significance.
• Understand the differences in potential and actual evapotranspiration.
• Consider the impact on different climates and local water availability.