The Journey of Water on the Surface
🌧️ Rainfall from Atmospheric Water Vapour
Water vapour is abundant in the Earth's atmosphere. When it condenses, it falls to the Earth's surface as precipitation. This rainfall appears in various forms and amounts depending on the region. The table shows rainfall levels across different cities.
| City | Average Rainfall (mm) |
|---|---|
| London | 620 |
| Cairo | 18 |
| Bogotá | 1,100 |
| Tehran | 229 |
| Kuala Lumpur | 2,500 |
| Manila | 2,347 |
| Singapore | 2,370 |
| Hilo | 3,300 |
| Quibdó | 7,328 |
| Mawsynram | 11,871 |
🌍 Water Coverage on Earth
More than 75% of the Earth's surface is covered with water, most of which forms salty bodies of water. All the water found in the Earth's surface and atmosphere (the hydrosphere) exists as liquids, solids, or vapours. This includes oceans, seas, rivers, lakes, underground waters, and glaciers.
🔬 Think like a Scientist
Question: How are clouds and rain formed?
Equipment: 2 glasses (or beakers), some balloon material, elastic bands, and ice
Method:
- Take two glasses. Fill one of them one-third full with warm water. Leave the other empty.
- Cover the mouth of both glasses with balloon material and secure it with elastic bands.
- Place a few pieces of ice on top of the balloon material covering each glass.
- Observe what happens and write down your observations.
- In which glass does cloud formation occur? In which one does rain form? Explain the reason.
Follow-up Question:
Show Answer
- Clouds form in the glass with warm water when the warm vapor rises and cools against the cold surface (balloon + ice), leading to condensation.
- Rain may form in the same glass if enough condensation collects and droplets fall. The empty glass won’t produce vapor, so no clouds or rain form there.
🌫️ How Rain Forms from Water Vapour
Just as in the past, sunlight heats the ocean surface. Water in oceans and seas evaporates and rises as vapour. In the upper atmosphere, due to lower temperatures, the vapour cools and condenses into tiny droplets. With continued cooling, as the air temperature drops and humidity increases, these droplets combine and form clouds. When the air becomes saturated, rainfall begins. If the air is very cold, moisture may fall as snow instead of rain.
If the condensation occurs at temperatures below 0°C, the moisture falls as snow. If raindrops pass through cold air on their way to the ground, they may turn into hailstones.
🌦️ The Role of Meteorology
Meteorology is the science that studies Earth's atmosphere and weather patterns. One of the most important tasks in meteorology is measuring rainfall. This is done using rain gauges at designated stations, and the amount is measured in millimeters.
💧 What Happens After Rainfall?
After rainfall, some of the water evaporates and rises into the atmosphere. Another portion flows across the surface of the land, while the remaining part infiltrates into the ground.
🏞️ Flowing Water and Drainage Basins
Some of the rainwater begins to travel across the land toward lower-lying areas. These waters join together and follow the slope of the land, flowing into lakes, seas, and oceans. The region where surface water is collected and directed by a river and its branches from higher to lower elevations is called a drainage basin.
🧪 Did you know?
Every drop of rain that flows into rivers eventually finds its way to the ocean — and may one day return as rain again through the water cycle.
🌊 Dams and Water Conservation
In the past, humans regarded water as a divine blessing. To manage it more effectively and prevent waste, people began building dams on rivers.
🏞️ River Flow Patterns
The speed of river water varies depending on different factors. A river may flow in a straight path or meander depending on the slope of the land. If the slope is steep and the water flows quickly, the river usually takes a straight path. However, when the land is flat and the slope is gentle, the river tends to form a winding or meandering path.
🌊 How Waterfalls Form
As a river continues its course, it may encounter a location with sudden changes in elevation. This results in the formation of a waterfall. Waterfalls typically form where the river flows from hard, resistant rock to softer rock. Over time, the softer layers erode more quickly than the harder layers above, causing a drop in the riverbed and forming a waterfall.
🚱 River Pollution
In the past, it was believed that due to the high volume of water in rivers, dumping waste into them would not cause pollution. However, we now know that rivers can become heavily polluted, especially from domestic and industrial wastewater. This pollution harms aquatic life and the surrounding environment.
Since rivers are a vital source of drinking, agricultural, and industrial water, they require greater protection and attention.
❓ QUESTIONS
1. In your opinion, what are the most important sources of river pollution?
👀 Show answer
2. What problems can river pollution cause?
👀 Show answer
🏔️ Natural Lakes and Their Importance
Lakes are bodies of water located in landlocked areas on Earth's surface. Naturally formed lakes have no open outlet to oceans or seas. They are dynamic ecosystems that support a wide range of wildlife. Lakes are essential for providing food, minerals, fossil fuels, and for regulating the regional climate. They are also important for transportation and tourism in surrounding areas.
The largest lake in the world is the Caspian Sea, which is called a lake due to its limited connection to other bodies of water. Lakes across different countries vary significantly in size and origin. Some are naturally formed, while others are man-made.
🏗️ Artificial Lakes and Human Use
Artificial lakes are created by humans for specific purposes. Many artificial lakes are formed behind dams. The stored water is used for electricity generation, irrigation, and drinking water.
Sometimes lakes are also constructed around cities for environmental improvement and climate moderation.
🌊 Oceans and Seas
About 97% of Earth’s water is stored in oceans and seas. Nearly 75% of Earth’s surface is covered by water. This is why the Earth appears blue when viewed from space.
The shape of shorelines varies in different places. In some coastal areas, the land is made of hard, resistant rocks, leading to rugged, rocky coastlines. In contrast, in other regions with softer coastal materials, the shoreline appears flat and sandy.
📌 Important Concept
Earth’s Surface is Mostly Water: About 97% of Earth’s water is found in seas and oceans, covering nearly 75% of the planet’s surface. This is why Earth appears blue when viewed from space.
🌊 Movement of Water in Oceans
Due to various natural factors, ocean water is always in motion. These movements appear as waves, ocean currents, and tides. Waves move water up and down, and also forward toward the shore. During earthquakes, waves can grow large and destructive, forming tsunamis that damage coastlines.
Tides are caused by the gravitational pull of the moon and sun. As the water rises and falls, the tide moves inland and then back out. Some countries use the power of tides to generate electricity. In historical times, warriors used low tide conditions to cross rivers strategically during battle.
❄️ Glaciers
In regions where the average air temperature stays below zero degrees Celsius, snowfall is more frequent. Over many years, this accumulated snow compacts and forms glaciers. These glaciers are typically found in high mountain areas.
Glaciers are broadly divided into polar glaciers and mountain glaciers. Massive polar glaciers are found in the Arctic and Antarctic regions. Mountain glaciers form on high-altitude areas of land, such as the example shown in Figure.
⚠️ Common Mistake
Don’t assume glaciers only exist at the poles — they also form in high mountain regions with cold climates.
❓ QUESTIONS
3. Describe the main stages of water’s journey on the Earth's surface as explained in the tutorial.
👀 Show answer
4. What physical processes drive the movement of water between different “reservoirs” such as the ocean, atmosphere, rivers, and groundwater?
👀 Show answer
5. Why is the water cycle considered a closed system on a planetary scale, and how does the tutorial illustrate this concept?