9. Water Cycle

Hydrologic Cycle

• Evaporation: Liquid water transforms into water vapor (gas).
• Condensation: Water vapor (gas) changes into liquid water.
• Precipitation: Rain and snow.
• Infiltration: Water seeps into the ground to become groundwater.
• Transpiration: Water release from trees.
• Runoff: Water flows over the land surface into rivers, oceans, lakes, and streams.

Human Activities & Water Cycle

• Withdraw freshwater faster than natural processes can replenish it.
• Aquifers are being reduced, and some rivers no longer reach the ocean.
• Deforestation increases runoff and reduces infiltration.

Water Supply and Sustainability

• Human activities interfere with the water cycle by increasing evaporation and decreasing infiltration.
• Dam construction alters water flow.
• Pollution contaminates water sources.

Causes of Water Shortage Due to Human Activities

• Increasing evaporation by storing water in reservoirs, using water for cooling, and irrigating crops.
• Decreasing infiltration through deforestation and creating impervious paved surfaces.

Sources of Water Pollution

• Point Sources: Pollution from concentrated, easily identified sources (e.g., sewage systems, factories, oil tanker spills).
• Non-point Sources: Pollution from diffuse, poorly defined sources (e.g., flood runoff).

Reducing Water Pollution

• Address flooding from streams caused by heavy rain (floodplains).

Groundwater Pollution

• Common pollutants: fertilizers, pesticides, gasoline, oil, and organic solvents.
• Spills of gasoline, oil, and organic solvents.
• Removing contaminants is difficult and costly due to slow flow and ineffective dilution.

Prevention of Water Pollution

• Prevent groundwater contamination.
• Reduce poverty and air pollution.
• Prevent yard waste from entering storm drains.
• Use manure to fertilize and avoid harmful chemicals down the drain.