Tropical and Dry Climates

Summary

This lecture explores tropical and dry climates, focusing on their formation and characteristics within the global atmospheric circulatory system. Tropical climates, covering 36% of Earth’s surface, experience consistent insolation and frequent precipitation due to the Intertropical Convergence Zone (ITCZ). The lecture covers sub-classifications, including tropical rainforests, monsoons, and savannas. Dry climates, characterized by permanent moisture deficits, are explored through examples like deserts and steppes. Contributing factors include subsiding air, orographic lifting, and continental interiors. A key concern discussed is the Sahel zone’s expansion, affecting sub-Saharan Africa and contributing to water scarcity issues.

Takeaways

• 😀 Tropical and dry climates are studied together due to their connection in the global atmospheric circulation system, particularly through the Hadley cells.
• 😀 Tropical climates cover about 36% of Earth's surface, and 37% of the global population lives in these regions.
• 😀 Tropical climates are mostly located between 20°N and 20°S of the equator, corresponding to the Tropic of Cancer and Tropic of Capricorn.
• 😀 The equator experiences consistent day lengths and direct insolation year-round, leading to warm temperatures and frequent precipitation.
• 😀 The ITCZ (Intertropical Convergence Zone) plays a key role in creating tropical climates by causing warm air to rise, cool, condense, and result in precipitation.
• 😀 Tropical rainforest climates are characterized by constant warmth, frequent rainfall, and little temperature variation throughout the year.
• 😀 Tropical monsoon climates have a dry season lasting one or more months, and are affected by seasonal winds bringing heavy rainfall, especially in regions like northern India.
• 😀 Tropical savanna climates are defined by a clear wet and dry season, with the ITCZ moving in and out, leading to more variation in rainfall and temperatures.
• 😀 Dry climates, making up 35% of Earth's surface, are associated with permanent moisture deficits, where evaporation exceeds precipitation.
• 😀 Deserts and steppes are examples of dry climates, often influenced by subsiding air from the subtropical high and geographic factors like mountains or continental interiors.

Q & A

What is the relationship between tropical and dry climates in the Earth's atmospheric circulation?

Tropical and dry climates are related through the Earth's atmospheric circulation, specifically the Hadley cells. Tropical climates, which receive a lot of insolation at the equator, are linked to the rising warm air that leads to cloud formation and precipitation. In contrast, dry climates occur around 30° North and South of the equator, where descending air from the Hadley cells becomes dry and leads to low precipitation.

Why are tropical climates found around the equator?

Tropical climates are found around the equator because of the direct insolation they receive year-round due to Earth's position relative to the Sun. The equator lies near the Tropics of Cancer and Capricorn, where the Sun's rays are most concentrated, leading to warm temperatures and consistent day lengths, which are key characteristics of tropical climates.

What are the three main subcategories of tropical climates?

The three main subcategories of tropical climates are the tropical rainforest, tropical monsoon, and tropical savanna climates. These subcategories are distinguished by the amount of time the Intertropical Convergence Zone (ITCZ) is present, with tropical rainforests having the ITCZ year-round, tropical monsoons for 6 to 12 months, and tropical savannas having it for less than 6 months.

What factors contribute to the consistent warmth and frequent precipitation in tropical rainforests?

Tropical rainforests experience consistent warmth and frequent precipitation due to the high levels of insolation, the presence of the ITCZ year-round, and convective lifting caused by local heating. The warm air rises, cools, condenses, and forms clouds, leading to regular rainfall, especially in the afternoon and mid-evening.

How do tropical monsoon climates differ from tropical rainforests?

Tropical monsoon climates differ from tropical rainforests mainly in the seasonal variation of precipitation. While tropical rainforests experience near-constant rainfall, tropical monsoons have a distinct dry season lasting one or more months. These climates are influenced by seasonal shifts in the ITCZ, and monsoon winds bring heavy rainfall during the wet season, usually associated with the southwest monsoon.

What is the distinguishing feature of a tropical savanna climate?

The tropical savanna climate is characterized by a distinct dry period when the ITCZ is not overhead. This dry period typically lasts from June to October, and the climate experiences a variation in temperature and precipitation. Unlike tropical rainforests, tropical savannas have grasslands with scattered trees, which is a result of less frequent rainfall.

What is the key difference in temperature patterns between tropical rainforests and tropical savannas?

In tropical rainforests, the temperature remains nearly constant throughout the year with very little variation, which is reflected in the flat line on climographs. In contrast, tropical savannas experience more temperature variation, with two temperature peaks during the year as a result of the Sun's direct rays moving between the Tropic of Cancer and Capricorn.

What are the main characteristics of dry climates?

Dry climates are characterized by a permanent moisture deficit, where evapotranspiration exceeds precipitation. These climates cover vast regions, especially between 15° and 30° North and South of the equator, and they typically include deserts and steppes. The lack of moisture is primarily due to descending dry air from the subtropical highs and the influence of mountains and rain shadows.

How does the Hadley cell contribute to dry climates?

The Hadley cell contributes to dry climates by causing the air to descend at around 30° North and South of the equator. As this air descends, it warms and dries out, leading to the formation of dry, subtropical high-pressure zones. This mechanism is responsible for creating arid conditions, particularly in deserts located in these regions.

What is the Sahel zone, and why is it a concern?

The Sahel zone is a semi-arid region located south of the Sahara Desert. It serves as a transition zone between the Sahara's hot, dry climate and the more temperate tropical savannas to the south. The Sahel has been experiencing a southward expansion of desertification, caused by factors like drought, deforestation, and population pressure, which poses a significant concern for the region's agriculture and water supply.