Why Does It Rain - A Simple Explanation for a Complex Phenomenon

As nature enthusiasts, it's important to explore the wonders of the natural world. One of the most captivating and essential phenomena is rain. Rain is one of the most common and important forms of precipitation on Earth. It provides fresh water for drinking, irrigation, and hydropower. It also shapes the landscape, nourishes the soil, and supports the biodiversity of plants and animals.

So, the next time you check your Barometer  you will know that rain plays a vital role in shaping our  ecosystems. In this blog post, we will dive into the fascinating science behind rainfall, uncovering the reasons why it rains and its significance for our planet.


The Water Cycle

To understand why it rains, we need to first understand the water cycle. The water cycle is the continuous movement of water between the Earth's surface and the atmosphere. It involves three main processes: evaporation, condensation, and precipitation.


It is when water changes from liquid to gaseous form. This happens when water on the surface, such as oceans, lakes, rivers, or plants, is overly heated and evaporates into thin air due to direct exposure to the sun. 


This is when water changes from gaseous to liquid form. When water vapour cools down as it rises higher in the atmosphere. The cooled water vapour forms tiny droplets of water or ice crystals around dust, pollen, smoke, or pollution particles. These particles are called cloud condensation nuclei (CCN). The droplets, or crystals stick together and form clouds.


When water falls from the clouds to the Earth's surface, it is called precipitation. This happens when the droplets or crystals in the clouds grow too large and heavy to stay suspended in the air. They fall as rain, snow, hail, or sleet, depending on the temperature and pressure of the air.

Factors Influencing Rainfall

Several factors contribute to the formation of rain clouds and subsequent precipitation:

  • Moisture: The availability of moisture in the atmosphere is essential for rain formation. Areas with high humidity or proximity to large water bodies tend to experience more rainfall.
  • Temperature: As moist air rises into the atmosphere, it cools, and the water vapour condenses. Cooler temperatures increase the likelihood of condensation and subsequent rainfall.
  • Atmospheric Instability: When the air in the atmosphere is unstable, meaning there are variations in temperature and humidity. It creates an environment conducive to cloud development and precipitation.
  • Atmospheric Lifting: When air masses encounter physical barriers like mountains, they are forced to rise. As the air rises, it cools, leading to cloud formation and rain.

Types of Rain

There are different types of rain depending on how the air rises and cools in the atmosphere. There are three main ways;

  • Relief rain - When air rises over a mountain or a hill, it cools down and condenses into clouds. The clouds produce rain on the windward side of the mountain or hill, where the air is moist and rising. The leeward side of the mountain or hill, where the air is dry and descending, receives little or no rain. This creates a rain shadow effect.
  • Convectional rain -  When air rises due to being heated by the sun. This happens mostly in tropical and equatorial regions, where the sun is strong and the air is warm and humid. The warm air rises quickly and forms cumulus clouds that look like cotton balls. These clouds can grow into cumulonimbus clouds that produce heavy showers and thunderstorms.
  • Frontal rain - When a warm body of air rises over a cold body of air. This happens mostly in temperate regions, where warm and cold air masses meet along fronts. A front is a boundary between two different air masses. When a warm front approaches a cold front, the warm air slides over the cold air and forms stratus clouds that produce light to moderate rain over a large area. When a cold front overtakes a warm front, the cold air pushes under the warm air and forces it up rapidly. This forms cumulonimbus clouds that produce heavy rain over a small area.


Understanding Other Effects of Rain

Rainfall is a remarkable natural phenomenon driven by the water cycle, atmospheric conditions, and various other influencing factors. Understanding why it rains not only expands our knowledge of the world around us but also helps us appreciate the delicate balance of our ecosystem. 

So, if you have one of our Barometers or are thinking of buying one, you will know when the rain is coming!