Grade 6 | Science | Unit 3 - Concept 2 - Lesson 1 - Farming the desert

Описание: Welcome dear students!
The previous pictures show different changes of weather, where :
• In picture (1), the sky was clear and bright.
• In picture (2), the sky became cloudy and rainy.
What are the causes that lead to this change in weather ?
• The density of cold and dry air is more than that of hot and humid air.
• When a part of air is heated by the Sun, it becomes hot and humid.
• When the hot and humid air meet the cold and dry air, the hot air rises.
• As the hot air rises, it becomes colder and this coldness causes water vapor in air to condense, then the rain falls.
How does a meteorologist predict what the weather will be ?
Meteorologist depends on some instruments to collect data and study changes of weather for long periods of time that help him to predict what the weather will be.
Properties of deserts :
• Rainfalls : Deserts receive about 250 millimeters of rain per year and this represents the least amount of rain compared to all other biomes.
• Weather : Deserts are characterized by extreme hot and dry weather, so farmers had to adapt to this climate and work to develop some ways to benefit from the small amount of water.
• Farming deserts : Farmers face a challenge in farming deserts because the extreme hot and dry weather that causes evaporation of more water than that falls by precipitation.
Improving the soil of deserts :
Population growth causes more people to live in desert, so farmers use new ways to make the soil of dry desert fertile and fruitful, for example :
• Soil : They improve the soil quality.
• Water : They use new ways to irrigate crops, such as reusing water.
• Crops : They plant crops that are able to grow in the hot climate and low-fertility soil.
• Energy : They use wind and the Sun to power their farms in desert with wind turbines or solar energy.
Mountain effects:
• Mountain ranges at coastal regions often have two sides:
• A wet side (that faces the coast).
• A dry side (that is away from the coast).
• Now, we will describe a process that causes a phenomenon at the dry side of coastal mountain ranges known as the "rain shadow".
Rain shadow phenomenon:
At the wet side that faces the coast:
• When warm and humid air encounters (faces) this side of a mountain range, so this air rises and cools.
• Water vapor in the cold air condenses, so the precipitation occurs.
At the dry side that is away from the coast:
The air descends and becomes warm, so this air dries the land of this side.
Changes in the atmosphere:
The following list shows a comparison between the properties of the atmosphere at the top of a mountain with the properties of the atmosphere at the bottom of the mountain:
The atmospheric pressure:
• High at the bottom of the mountain
• Low at the top of the mountain
The air temperature:
• High at the bottom of the mountain
• Low at the top of the mountain
The air density:
• High at the bottom of the mountain
• Low at the top of the mountain
we can conclude that the atmospheric pressure (air pressure), air temperature and air density decreases as we go from the bottom of the mountain to its top.

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Mr. Raouf Ashraf