water resources
4.1 Introduction
Water is a vital resource for life.
Essential for various economic activities.
Increasing population causes severe stress on water resources.
Insufficient water limits food production.
Role of Water
All living organisms need water for growth and reproduction.
Critical for the existence of life.
Acts as a climate moderator.
Necessary for photosynthesis.
Atmospheric water combined with temperature affects global ecology.
4.2 Worldwide Supply, Renewal, and Distribution
97% of Earth's water is in oceans and seas (saline).
Only 3% is fresh water.
2.997% locked in ice caps/glaciers.
0.0035% available as soil moisture, exploitable groundwater, lakes, streams, and water vapor.
Water Cycle
Key Processes
The sequence from atmosphere to landmasses and oceans and back is termed the Hydrological Cycle.
Fresh water is continuously collected, purified, and distributed through this cycle.
Factors controlling evaporation and transpiration include temperature, humidity, and wind.
Involves circulation of mass among the lithosphere, hydrosphere, and atmosphere.
Stages of the Cycle
Evaporation: Transformation of water into vapor from all water bodies.
Condensation: Change of vapor into liquid, forming clouds in the troposphere.
Precipitation: Water returns to Earth as rain, snow, hail, or sleet.
Runoff: Rainfall and its consequences on land, including percolation into groundwater or surface water accumulation.
Human Interference in Water Cycle
Overloading water with waste can disturb the natural cycling and purification process.
Extracting groundwater faster than replenishment deteriorates water quality and impacts the hydrological cycle.
Ground Water
Defining Ground Water:
Found underground in soil, sand, and rock.
Contaminated by industrial waste, making restoration challenging.
Groundwater Zones
Unsaturated Zone: Contains air and minimal water between Earth’s surface and the water table.
Saturated Zone: All spaces filled with water, where groundwater is stored.
Vadose Zone: Region of unsaturated soil above the water table.
Aquifers: Geological formations that hold significant amounts of water, can be confined (under pressure) or unconfined (atmospheric pressure).
Impacts of Groundwater and Aquifers
The porosity and permeability of aquifers determine groundwater flow and storage.
Unsustainable withdrawal can lead to the depletion of water tables and the formation of a cone of depression.
Surface Water and Watersheds
Surface water includes streams, lakes, and reservoirs.
Watersheds: Areas draining water into surface water bodies, impacting runoff.
Floods
Defined as the overflow of water onto typically dry land, occurring when water exceeds the capacity of rivers.
Floodplains are fertile areas created by sediment deposition during floods.
Drought
A prolonged shortage in water supply causes devastation, particularly impacting agriculture and leading to food insecurity.
Consequences: Desertification and famine due to water scarcity.
Desertification
Refers to the degradation of dryland ecosystems due to climatic variations and human activities.
Major causes include deforestation, over-cultivation, and mismanagement of resources.
Famine
Extreme food shortages cause increased mortality rates, particularly affecting vulnerable populations.
Driven by natural disasters and socio-political factors.
Environmental Impacts of Large Dams
Categories of Impact
Impacts within Dam Reservoirs: Flood surrounding habitats, displacing ecosystems.
Downstream Effects: Altered sediment flow leading to erosion and loss of habitat.
Regional Effects: Infrastructural impacts causing environmental degradation.
Specific Effects
Flooding can release greenhouse gases like methane from decaying plant material.
Lack of sediments in rivers negatively impacts aquatic ecosystems and coastal areas.
Construction and communities near dams can lead to habitat loss and increased erosion.