Hydrological cycle

Topics Covered

  • Hydrological cycle

  • Hydrological processes

  • Human usage of the hydrological cycle

  • Required reading:

    • Smithson et al. (2008). Fundamentals of the Physical Environment. Routledge, Chapters 5, 14, 313-324.

    • Huddart and Scott (2010). Earth Environments, Chapters 4.1-4.2, 8, 8.4.

Outline of the Course

  • Introduction to the hydrological cycle

  • Aspects of the hydrological cycle

  • Importance of the hydrological cycle

  • Assessing the hydrological cycle

  • Human usage of the hydrological cycle

Introduction to the Hydrological Cycle

  • All processes are driven by solar energy including wind and precipitation.

  • Earth's properties influence the geography and details of these processes.

Energy Budget of Earth and its Atmosphere

  • Solar Radiation:

    • Incoming: 100 units

    • Outgoing: 100 units

    • Breakdown: 30 units reflectance, 64 units long wave loss to space.

  • Absorption Breakdown:

    • Absorption by the atmosphere: 9 units

    • Absorption by Earth's surface: 51 units

    • Energy transport to the atmosphere by conduction/convection: varying units.

Importance of the Hydrological Cycle

  • Meteorological and Climatological Role:

    • Oceans: global heat transfer, trace gas uptake, precipitation source.

    • Atmosphere: global heat distribution.

    • Evapotranspiration: influences air stability and surface cooling.

The Global Hydrological Cycle

  • Interlinked system of water stores and flows driven by solar energy.

  • Fluxes include:

    • Evaporation: Mainly from oceans; 10% rains back onto land = runoff.

    • Recycling: The process of reusing water from evaporation and precipitation.

Aspects of the Hydrological Cycle

  • Heat Transfers and Global Circulation:

    • Energy transfers measured at 10^19 kilocalories/year.

  • Generation of Precipitation:

    • Requires cooling, driven by lifting processes such as convection and frontal shifts.

Precipitation Patterns

  • Zonal Precipitation:

    • Influenced by wind patterns, temperature, and pressure distributions.

  • Precipitation Regimes:

    • Differences between summer and winter precipitation based on circulation cells.

The Role of Vegetation in the Hydrological Cycle

  • Transpiration: Loss of water vapor from plants essential for returning moisture to the atmosphere.

  • Evapotranspiration: Sum of evaporation and transpiration, critical to water cycles especially in continental areas.

Biological Significance of the Hydrological Cycle

  • Vital for biochemical processes such as photosynthesis and respiration.

    • Photosynthesis formula: 6CO2 + 12H2O + energy → C6H12O6 + 6O2 + 6H2O.

  • Water's role in cell structure and physiology crucial for nutrient uptake and growth.

Human Significance of the Hydrological Cycle

  • Physiological Needs:

    • Importance of hydration, food production (average diet requires significant water amount).

  • Environmental Hazards:

    • Flooding, ice hazards, and the role of water in recreation and cooling.

Assessing the Hydrological Cycle

  • Major Water Reservoirs:

    • 97% in oceans, 2% in ice caps, rest in lakes, rivers, and soil moisture.

  • Mass Budgets:

    • Balance of water processes (precipitation, irrigation, evaporation) in hydrological assessments.

Conclusion

  • Summary Insights:

    • The hydrological cycle is closed and dynamic, linked to other Earth systems; largely oceanic precipitation; reflects climate interactions.

    • Per person yearly water requirement ~1700m³; inefficient water usage presents significant challenges for future sustainability.