Monsoons bring a seasonal change in weather to many parts of the world. This lesson will explore two monsoonal circulations and will also discuss how monsoons impact the people who experience them.
What is a Monsoon?
About 65% of the world’s population lives in regions affected by monsoons, and the rain that comes from the monsoons impacts the food sources in those areas. In fact, in India and other parts of Asia, the monsoons are so linked to crops, there are two sets of crops: those grown during the wet monsoon season, or the kharif crops, and those grown during the dry season, or rabi crops.Although the terms ‘kharif’ and ‘rabi’ might be foreign to you, I bet you would recognize some of the plants grown during each crop.
For example, the kharif crops include rice, peas, corn, and millet; whereas the rabi crops include barley, wheat, and oats. And farming is big business in India, with 70% of Indians either directly or indirectly affected by farming.So, you might get that monsoons are pretty important, but what are they? Well, for starters, they are winds that change direction depending on the season. This wind change also brings a change in weather. These changes in weather bring rains, which allow kharif crops to flourish, or dry weather, which allows rabi crops to be successful.Although monsoons can bring welcomed rain, they can also cause dangerous flash floods and landslides, which can kill people, crops, and livestock.
And India isn’t the only place in the world that has to deal with monsoons. In fact, other parts of Asia, Africa, South America, and (believe it or not) even North America have monsoons. But India experiences the most intense monsoons, so you can say it’s the poster child for monsoons.But what causes a monsoon? Well, it might not seem like the land and oceans would have much to do with the wind in the air, but they’re all connected. Let’s zoom in on India to investigate how monsoons form.
We’ll focus on the circulation of air between a landmass and the ocean.
Let’s take a look at the landscape, since that impacts whether or not a monsoon will form. We’ll focus on two monsoonal circulations: summer and winter.
Let’s start with summer. You’ll notice there is an ocean along with a large landmass, and you might also notice it’s a sunny day. In fact, in this region, it is actually early summer, which you may have already gathered!
Now, let’s check out the ocean. During the early summer, the land heats quicker than the ocean so the air above the ocean is cooler and denser than the air above the landmass.
This creates an area of high pressure. This is because the air molecules are moving slower and are closer together, therefore exerting more pressure on their surroundings.So, what does all of this high and low pressure have to do with a monsoon? Well, you may have heard this somewhere already, but air will flow from areas of high pressure to areas of low pressure and this flow of air is actually wind.If you check out our ocean and landmass, you can see that air is going to flow from the colder, denser ocean air to the warmer low-pressure air on land. That’s only part of the monsoon story. The warm air above the land is going to rise because it is less dense and when the cold, moist air from the ocean flows inland, the warm air carries the cold air up with it.
As the cold air rises, it cools even more and reaches saturation, meaning it can’t hold any more water vapor. When this happens, clouds form, and then rain. This is the start of the Indian wet season as well as the kharif crop season, or the summer monsoon. And India receives about 75% of its total annual rainfall during this monsoonal season, so you can see why it’s important to those water-loving crops.
Now, let’s look at another monsoonal circulation, or what happens in late fall or early winter.
The ocean is going to warm faster than the landmass, so things are going to flip. The air over the ocean is warm, which creates a low pressure system, while the air over the land mass is cold and dense, which creates a high pressure system.Remember, wind blows from high pressure to low pressure, so the wind’s going to be blowing from the land to the ocean.
When the cold air from the land reaches the warm air from the ocean, it’s forced upward with the warm air. As it rises, it cools and becomes saturated so clouds and precipitation form. This keeps the land dry, with precipitation falling over the ocean.
And for India, this is the rabi season. So Indian farmers make the best of the summer and winter monsoonal circulations.
Monsoons, or seasonal winds that bring a change in weather, are a welcoming relief in many parts of the world, but they can also wreak havoc in the form of flooding and storms. Let’s take a moment to review the summer and winter monsoonal circulations for India.
In the early summer, the land heats up quicker than the ocean, which creates a low-pressure system on land and a high-pressure system in the ocean. Wind blows from high to low pressure, so wind blows inland. As this cooler air blows inland, it’s forced upward by the warm, rising air above the land.
As it rises, the air cools, reaches saturation, forms clouds and precipitation.Now, in the late fall or early winter, this is reversed. The ocean is warmed more quickly than the landmass, so the high-pressure system is now above the land and the low-pressure system is above the ocean. And since wind blows from high to low pressure, wind blows out to the ocean. As the colder, land air blows to the ocean it’s forced upward by the less dense, rising warm ocean air and, as it rises, it cools, reaches saturation, forms clouds and precipitation.People around the world have come to depend on these seasonal winds for crops, as you witnessed with the kharif and rabi crops of India.
So, the next time you drink some soy milk or have some rice with dinner, you can think of India and the monsoons!
Knowledge of this lesson’s facts could enable you to:
- Provide details about monsoons
- Compare summer and fall monsoon seasons
- Emphasize the effects of monsoons on India’s kharif and rabi crops