4.1 Introduction to Water Systems

4.1 Introduction to Water Systems Globally

  • 1.2 billion people live in areas with inadequate water supply.

    • Source: International Water Management Institute

The Hydrological Cycle

  • The hydrological cycle is a system of water flows and storages that can be disrupted by human activity.

  • The ocean circulatory system, also known as the ocean conveyor belt, influences climate and the global distribution of water (matter and energy).

Knowledge & Understandings

  • Solar radiation drives the hydrological cycle.

  • Freshwater comprises only approximately 2.6% of the Earth's water storages.

  • Key storages in the hydrological cycle:

    • Organisms, soil, oceans, groundwater (aquifers), lakes, rivers, atmosphere, glaciers, and ice caps.

  • Flows within the hydrological cycle include:

    • Evapotranspiration, sublimation, evaporation, condensation, advection, precipitation, melting, freezing, flooding, surface runoff, infiltration, percolation, stream-flow, and currents.

  • Human activities such as agriculture, deforestation, and urbanization significantly impact surface runoff and infiltration.

  • Ocean circulation systems are influenced by temperature and salinity differences, which drive water density variations, leading to the ocean conveyor belt's effects on climate.

Application & Skills

  • Discuss the human impact on the hydrological cycle.

  • Construct and analyze a hydrological cycle diagram.

Theory of Knowledge

  • The hydrological cycle is represented as a systems model. Consider the extent to which systems diagrams effectively model reality, given their basis in limited observable features.

The Importance of Water

  • Water is essential for life.

  • Moderates climate, sculpts land, removes wastes and pollutants, and moves continually through the hydrological cycle.

Flows & Storages in the Water Cycle

  • Flows include:

    • Evaporation, transpiration, sublimation, condensation, advection, precipitation, melting, freezing, flooding, surface runoff, infiltration, percolation, stream flow, currents.

  • Storages include:

    • Organisms, oceans, groundwater (aquifers), lakes, soil, rivers, atmosphere, glaciers, and ice caps.

Earth’s Water Budget

  • There is a limited amount of water available on Earth; not all is in usable form.

  • Water can be a renewable or non-renewable resource:

    • Non-renewable: Oceans and icecaps (long storage).

    • Renewable: Atmosphere and rivers (move quickly through the cycle).

Distribution of Earth's Water

  • 97% saline (oceans), 3% fresh water:

    • Ice caps and glaciers: 68.7%

    • Lakes: 87%

    • Other freshwater (swamps, rivers): 0.9% and 2% respectively.

  • 41% of the world’s population lives in river basins with inadequate freshwater.

    • Observations: Rivers running dry, shrinking lakes and seas, and falling water tables due to over-pumped aquifers.

Human Impacts on the Water Cycle

  • Overuse for homes, agriculture, irrigation, and industry.

  • Notable rivers affected:

    • Colorado River & Rio Grande (N. America), Indus River (Pakistan), Yellow River (China), and others.

Stress on River Systems

  • Comparative analysis of available water versus human usage across different continents.

Desertification

  • Defined as land degradation where dry land regions become increasingly arid, resulting in water loss, and loss of vegetation and wildlife.

  • Causes include climate change and human activities.

Case Study: The Aral Sea Disaster

  • Once the world's fourth largest freshwater lake, now heavily impacted by irrigation practices.

  • Major ecological, economic, and health disaster due to water diversion from its feeder rivers.

    • 85% wetlands eliminated, 50% of local species disappearing, tripled salinity, and extinction of native fish species.

Groundwater Issues

  • 20% of the world’s aquifers are being over-pumped.

  • Recovery rates of groundwater recharge vary significantly across regions.

Case Study: Aquifer Depletion in India

  • The Upper Ganges is being excessively pumped, leading to potential unusability due to pollutants.

Advantages and Disadvantages of Groundwater Withdrawal

  • Advantages:

    • Usability for drinking and irrigation, availability year-round, low extraction costs, no evaporation losses.

  • Disadvantages:

    • Over-pumping can lead to land subsidence, well contamination, reduced natural water flow, and increased depth for extraction.

Solutions to Groundwater Depletion

  • Prevention strategies:

    • Encourage conservation, regulate withdrawals, and avoid water-intensive crops in dry areas.

  • Control strategies:

    • Price regulation and taxation of water removal.

Pollution and Human Impacts

  • Pollution sources such as fertilizers and industrial waste significantly contaminate freshwater.

  • Changing the natural flow of rivers due to human constructions contributes to environmental challenges.

River Management Challenges

  • Human activities such as river straightening and dam construction aim to prevent flooding but can have adverse effects.

Case Study: China’s Three Gorges Dam

  • Pros and cons debated, with potential benefits in electricity generation and transportation contrasted against displacement and ecological risks.

Flooding Events

  • Caused by rainfall, snowmelt, vegetation loss, and wetlands destruction.

  • Floodplains provide natural flood control and support water quality and groundwater recharge.

Urbanization and Flooding

  • Rapid runoff exacerbated by urbanization increases flood risks; sediment and debris contribute to blockage and increased flooding.

Ocean Currents and Energy Distribution

  • Major role in distributing energy globally, influenced by wind and thermohaline currents based on density differences.

Coastal Climate and the Ocean

  • Water influences coastal climates by moderating temperature changes and increasing humidity and precipitation through evaporation.

Homework Assignment

  • Read pages 198-206 and complete tasks on page 201.

  • March 22 is recognized as World Water Day.