Tropical Climates
Koeppen’s Climate Classification
Moisture
Coldest
month
Warmest
month
-
>18C
-
Evap>Rain
-
-
Temperate
-
<18C, >-3C
>10C
Cold
-
< -3C
>10C
Polar
-
-
<10C
Tropical
Dry
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Koeppen’s Climate Classification
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Important Climate Types for
the Tropics
• Tropical wet climate
– Rain all year round
– Short dry season - Monsoon
– Winter dry season
• Semi arid (< 750 mm)
• Desert or arid climate
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Climates in the Tropics
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Climate Determinants
•
•
•
•
Solar radiation
Surface receiving solar radiation
Earth’s rotation
Land/sea configuration and topography
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500
400
300
200
0
100
Ja
n
Fe
b
M
ar
Ap
r
M
ay
Ju
n
Ju
ly
Au
g
Se
p
O
ct
No
v
De
c
Solar Radiation (W/m2/day)
Solar Radiation at the Equator
High solar radiation with little seasonal variation (6%) at the Equator
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500
400
300
200
0
20
100
Ja
n
Fe
b
M
ar
Ap
r
M
ay
Ju
n
Ju
ly
Au
g
Se
p
O
ct
No
v
De
c
Solar Radiation (W/m2/day)
Solar Radiation at the Equator and 20 N
20% seasonal variation in solar radiation at 20° N latitude
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500
400
300
200
100
0
20
40
Ja
n
Fe
b
M
ar
Ap
r
M
ay
Ju
n
Ju
ly
Au
g
Se
p
O
ct
No
v
De
c
Solar Radiation (W/m2/day)
Solar Radiation at the Equator,
20 N and 40 N latitude
Less solar radiation with much seasonal variation (50%) at 40° N
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Solar Radiation Absorption
Receiving Surfaces
•
•
•
•
Land
Bare soil
Dry soil
Dark soil
• Warmer
• Low
•
•
•
•
Water
Vegetation
Wet soil
Light soil
• Cooler
• High
Temperature
Pressure
Airflow
• Low
• High
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Humidity
Solar Radiation Drives the
Climatic System
• Tropical Region
– High consistent levels of incoming
solar energy
– 75% of surface as water - thus
much moisture
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Air Flow in the Tropics
• High solar input heats up
air
– Warmer air rises
– Creates a low pressure area
– Causes air flow from the
higher pressure zone at
higher latitude
• Trade winds are
the result
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Tropical Trade Winds
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Intertropical Convergence Zone
Tropic of Cancer - 23.5° N
Equator
Intertropical Convergence Zone
Tropic of Capricorn - 23.5° S
• ITCZ where trade winds converge
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Intertropical Convergence Zone
July
Intertropical Convergence Zone
Equator
January
• ITCZ follows the sun and modified by topography
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Moisture
• Air temperature is correlated to water
holding capacity of air
• Tendency for higher rainfall in tropics
– Can be very intense showers
– Associated with the ITCZ
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Color codes:
Reddish tones = no dry season
Blue tones = short dry season
Yellow and green = distinct dry season
Highest
rain
along
the
ITCZ
Intertropical Convergence Zone
Temperature of the coldest month is > 18C (64.4F)
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Color codes: Grays and blue = steppe climate
Shades of orange = deserts
Yellows = cool dry deserts
The major deserts of the world are towards edge of tropical zone
Intertropical Convergence Zone
Annual evaporation exceeds annual
precipitation
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Temperature in the Tropics
• Little annual variation (<10°F or 6°C)
• Daily range is typically greater than mean monthly
temperature range
• Cooler temperatures at higher altitude
– 3°F/1000 feet or 5.6°C/1000 m
• Warmer temperatures in continental interiors
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What is the Tropics?
• Three climate influencing characteristics
unique to the tropics
– High solar radiation
– Little seasonal variation in solar radiation
– 75% of surface area is water
• Main classification points
– Moisture
– Altitude
• No one unique tropical climate
– Very wet to very dry
– Windy to relatively calm
– Very hot to cold
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Tropical Soils
Tropical vs Temperate Zone Soils
• Older land surfaces
– Most temperate areas exposed since last
glaciation
– Exceptions: volcanic and alluvial soils
• More highly weathered and leached
– High temperature/moisture
– Weather 4 times faster
– Poor natural fertility
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Old Landscape Soils
• 54% of land area
– Oxisols, 25%
• Brazil and Zaire
– Ultisols, 12%
• Brazil, West coast of Africa, NE India, Borneo
– Alfisols, 17%
• Sahelian and Sudanian zones
• Kenya, Tanzania, NE Brazil, India
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Oxisols in the Tropics
O
O
O
O
O
O
O
O
O
O O
O
25% of land area
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Oxisols - 25%
•
•
•
•
•
•
•
•
Humid tropics
Low pH
Low CEC
Low exchangeable bases, Al, P
Low fertility
Excellent drainage
Good to excellent erosion resistance
Agricultural potential
– Low in low input system
– High in high input system
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Ultisols in the Tropics
U
U
U
U
U
U
U
U
U
U
U
U
U
U
12% of land area
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U U
Ultisols - 12%
•
•
•
•
•
•
•
•
Humid tropical forest, Asia
Low pH
Low CEC
Low exchangeable bases, P - high Al
Low fertility
Excellent drainage
Poor to good erosion resistance
Agricultural potential
– Low in low input systems
– Good - high in high input system
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Alfisols in the Tropics
A
A
A
A A
A
A
A
A
A
A
A
17% of land area
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A
Alfisols
•
•
•
•
•
•
•
•
Transitional zone to arid climate
High pH
Medium CEC
Medium to high exchangeable
bases
Medium to high fertility
Good to excellent drainage
Poor to good erosion resistance
Agricultural potential
– Good for low input system
– High for high input system
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New Landscape Soils
• Alluvial, Volcanic, and other soils 23%
– Entisols and Inceptisols
• Desert soils
20%
– Aridisols
• Cracking soils
3%
– Vertisols
• Peaty soils
<1%
– Histosols
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Inceptisols and Entisols in the Tropics
I
I
E
E
I
E
I
I
I
I
I
I
I
I
I
E
I
I
E
E
I
I
E
E
23% of land area
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I
I
E
I
I
I
I
I
Inceptisols and Enceptisols
New, little weathered soils
Vary in characteristics
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Alluvial Soils
•
•
•
•
•
River flood plains
Wide range of physical/chemical traits
Very fertile
Flood control is important
Location - Tropical River Basins
– Amazon, Orinoco
– Congo, Senegal, Niger
– Ganges, Mekong
• Already extensively farmed
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Volcanic soils
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Volcanic Soils
• Advantages
–
–
–
–
Excellent drainage
Stable porous structure, resistant to erosion
No drought or tillage problems
Abundant Ca, Mg, and K
• Disadvantages
– P fixation and low N
– Generally at high altitude
• Cooler climate
• Poor access
– Already extensively farmed
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Aridisols in the Tropics
D
D
D
D
D
D
D
D
D
D
D
D
20% of land area
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D
D
Aridisols - Desert soils
• Developed in dry regions so little
weathering
• Little leaching so good fertility
• May have accumulations of sodium,
gypsum, or salt
• Potential if water is available for
irrigation and leaching
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Vertisols in the Tropics
V
V
V
V
3-5% of land area
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V
Vertisols
• Characteristics
–
–
–
–
–
High in montmorillonite clay
Cracks when dry
High pH, Ca, and Mg
Good fertility
Excellent potential for
agriculture
• Disadvantages
– Difficult to till if dry or too wet
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Histosols
• Soils with peaty accumulations
• 75% of these soils in SE Asia
• Sumatra, Borneo, Indonesia
• Most have low base status
• Good N levels
• Low P, K and other cations
• Micronutrient deficiencies (Zn,
Cu) common
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Histosols - Peaty soils
• Soils with peaty accumulations
• Need to be drained before use
• Deep peats, pineapple production
• Shallow peats, rubber, oil palm, coffee
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Fertility Levels of Tropical Soils
•
•
•
•
•
•
•
Alluvial
Vertisols
Aridosols
Volcanic
Alfisols
Ultisols
Oxisols
most fertile
least fertile
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Extent of Tropical Soils
•
•
•
•
•
•
Oxisols
Aridisols
Alfisols
Ultisols
Vertisols
Alluvial
25%
20%
17%
12%
5%
5%
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Structure of Tropical Soils
•
•
•
•
•
Volcanic
Oxisols
Alfisols
Ultisols
Vertisols
Best soil structure
Worst soil structure
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Any Questions?
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