12.1. HYDROLOGICAL CYCLE

The hydrological cycle describes the movement of water on, in, and above the earth. The water cycle has been working for billions of years and all life on earth depends on it.

The hydrological cycle, also known as the water cycle, is the continuous movement of water on the planet. It includes processes like evaporation, condensation, precipitation, and runoff. This cycle has existed for billions of years, making it crucial for life on Earth, as it supplies fresh water for drinking, agriculture, and ecosystems.

Think of the hydrological cycle as a huge water recycling machine. Just like a machine that filters and reuses water, the hydrological cycle ensures that water is constantly moving and transforming from one state to another, such as from liquid to vapor and back again, nourishing plants and animals along the way.

The distribution of water on earth is quite uneven. Many locations have plenty of water while others have very limited quantity.

Water is unevenly spread across the globe, with about 71% of Earth covered in oceans. However, only a small fraction of this water is freshwater, which is vital for human use, agriculture, and biodiversity. Some areas, like deserts, have very limited water resources, leading to water scarcity, while other regions may have abundant water sources.

Imagine a large pizza where some slices are thick with toppings (representing areas with lots of water) while others are nearly empty (representing drier areas). Although the pizza is plentiful, some slices are much more enjoyable because they have more cheese and toppings, just like some areas of the earth have much more water available for use.

The hydrological cycle refers to the circulation of water within the earth’s hydrosphere in different forms, i.e., the liquid, solid, and the gaseous phases.

The hydrological cycle involves various phases: liquid (water), solid (ice or snow), and gas (water vapor). Water can change from one form to another throughout the cycle. For example, when the sun heats water in rivers or oceans, it turns into vapor (evaporation), and when that vapor cools, it forms clouds (condensation). Eventually, the water falls back to the earth as precipitation (rain or snow).

You can think of water's phases like a stage performance where the actors change their costumes. The water (actor) can show up as a liquid in lakes, a solid in ice packs, or as a gas in the air. Just as actors keep their roles separate but also work together to create a story, water can change forms but is always part of the hydrological cycle.

It is to be noted that the renewable water on the earth is constant while the demand is increasing tremendously. This leads to water crisis in different parts of the world — spatially and temporally.

Although the total amount of renewable water on Earth remains constant, the growing population and increased water usage (for agriculture, industry, and personal consumption) cause stress on these resources. Areas facing drought or pollution are particularly vulnerable, which creates a situation where many places have limited access to clean water, leading to a water crisis.

Consider a bank where the total money does not grow, but more and more people want to take out loans. If everyone tries to take more money than is available, some will end up empty-handed. Similarly, with water, as more people need it, some regions can't meet this demand, leading to shortages.

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