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.