Environmental Studies (AKU-ENV)
Topic 3 of 7Aga Khan Board

Water Resources

Freshwater availability, the water cycle, dams and water scarcity in Pakistan

The Water Cycle (Hydrological Cycle):

  • Evaporation: Sun heats water → water vapour rises
  • Transpiration: Plants release water vapour (evapotranspiration = both combined)
  • Condensation: Water vapour cools → forms clouds (water droplets)
  • Precipitation: Rain, snow, sleet, hail falls
  • Surface run-off: Water flows into rivers and lakes
  • Infiltration: Water soaks into soil → groundwater stores
  • Groundwater flow: Slow movement through rock → springs, wells

    • Freshwater scarcity: Only 2.5% of Earth's water is freshwater; most is frozen in glaciers or underground. Available freshwater is unevenly distributed.


    Dams provide: water storage for irrigation, drinking water, hydroelectric power, flood control.

    Disadvantages: displaces communities, disrupts fish migration, sedimentation reduces lifespan.


    Pakistan's water challenges:

  • Declining Indus River flow (glacier melt disrupting seasonality)
  • Waterlogging and salinity (over-irrigation in Sindh and Punjab)
  • Groundwater depletion (Lahore, Karachi pumping faster than recharge)
  • Only 36% of Pakistanis have access to safe drinking water

    • Water conservation: drip irrigation (reduces agricultural water use by 50%), rainwater harvesting, reducing industrial water use, pricing water appropriately.

    Key Points to Remember

    • 1Water cycle: evaporation → condensation → precipitation → run-off
    • 2Only 2.5% of Earth's water is fresh; most is frozen or underground
    • 3Dams: water storage + hydropower vs displacement + sedimentation
    • 4Pakistan water challenges: salinity, groundwater depletion, glacier disruption

    Pakistan Example

    Tarbela Dam — Pakistan's Lifeline and Its Challenges

    Tarbela Dam on the Indus River (1974) is one of the world's largest earth-filled dams — 143 m high, generating 4,888 MW. It irrigates millions of hectares of Punjab and KPK farmland. However, sedimentation is reducing its storage capacity (estimated lifespan already shortened by decades), and upstream glacier changes are altering seasonal water flow — all critical AKU Environmental Studies themes.

    Test Your Knowledge!

    3 questions to check if you understood this topic.

    Start Quiz
    Pollution & Waste ManagementBiodiversity in Pakistan