Tropical Climates

Tropical Horticulture - Texas A&M University Koeppen’s Climate Classification

Tropical Horticulture - Texas A&M University Koeppen’s Climate Classification

Tropical Horticulture - Texas A&M University 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

Tropical Horticulture - Texas A&M University Climates in the Tropics

Tropical Horticulture - Texas A&M University Climate Determinants Solar radiation Surface receiving solar radiation Earth’s rotation Land/sea configuration and topography

Tropical Horticulture - Texas A&M University High solar radiation with little seasonal variation (6%) at the Equator

Tropical Horticulture - Texas A&M University 20% seasonal variation in solar radiation at 20° N latitude

Tropical Horticulture - Texas A&M University Less solar radiation with much seasonal variation (50%) at 40° N

Tropical Horticulture - Texas A&M University 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 Humidity

Tropical Horticulture - Texas A&M University Solar Radiation Drives the Climatic System Tropical Region –High consistent levels of incoming solar energy –75% of surface as water - thus much moisture

Tropical Horticulture - Texas A&M University 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

Tropical Horticulture - Texas A&M University Tropical Trade Winds

Tropical Horticulture - Texas A&M University Intertropical Convergence Zone ITCZ where trade winds converge Tropic of Cancer ° N Tropic of Capricorn ° S Equator Intertropical Convergence Zone

Tropical Horticulture - Texas A&M University Intertropical Convergence Zone ITCZ follows the sun and modified by topography Equator Intertropical Convergence Zone July January

Tropical Horticulture - Texas A&M University 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

Tropical Horticulture - Texas A&M University Color codes: Reddish tones = no dry season Blue tones = short dry season Yellow and green = distinct dry season Temperature of the coldest month is > 18C (64.4F) Highest rain along the ITCZ Intertropical Convergence Zone

Tropical Horticulture - Texas A&M University Annual evaporation exceeds annual precipitation Color codes:Grays and blue = steppe climate Shades of orange = deserts Yellows = cool dry deserts Intertropical Convergence Zone The major deserts of the world are towards edge of tropical zone

Tropical Horticulture - Texas A&M University 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

Tropical Horticulture - Texas A&M University 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

Tropical Soils

Tropical Horticulture - Texas A&M University 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

Tropical Horticulture - Texas A&M University 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

Tropical Horticulture - Texas A&M University Oxisols in the Tropics O O OO O O O O O O O O 25% of land area

Tropical Horticulture - Texas A&M University 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

Tropical Horticulture - Texas A&M University Ultisols in the Tropics U U U U U U U U U UU U UU U U 12% of land area

Tropical Horticulture - Texas A&M University 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

Tropical Horticulture - Texas A&M University Alfisols in the Tropics A A AA A A A A A A A A A 17% of land area

Tropical Horticulture - Texas A&M University 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

Tropical Horticulture - Texas A&M University New Landscape Soils Alluvial, Volcanic, and other soils 23% –Entisols and Inceptisols Desert soils 20% –Aridisols Cracking soils 3% –Vertisols Peaty soils <1% –Histosols

Tropical Horticulture - Texas A&M University Inceptisols and Entisols in the Tropics I I I I I I I I I I I I I I I I I I I I I I I E E E E E E E E E 23% of land area

Tropical Horticulture - Texas A&M University Inceptisols and Enceptisols New, little weathered soils Vary in characteristics

Tropical Horticulture - Texas A&M University 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

Tropical Horticulture - Texas A&M University Volcanic soils

Tropical Horticulture - Texas A&M University 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

Tropical Horticulture - Texas A&M University Aridisols in the Tropics D D D DD D D D D D D D D D 20% of land area

Tropical Horticulture - Texas A&M University 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

Tropical Horticulture - Texas A&M University Vertisols in the Tropics V V V V V 3-5% of land area

Tropical Horticulture - Texas A&M University 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

Tropical Horticulture - Texas A&M University 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

Tropical Horticulture - Texas A&M University Histosols - Peaty soils Soils with peaty accumulations Need to be drained before use Deep peats, pineapple production Shallow peats, rubber, oil palm, coffee

Tropical Horticulture - Texas A&M University Fertility Levels of Tropical Soils Alluvialmost fertile Vertisols Aridosols Volcanic Alfisols Ultisols Oxisolsleast fertile

Tropical Horticulture - Texas A&M University Extent of Tropical Soils Oxisols25% Aridisols20% Alfisols17% Ultisols12% Vertisols5% Alluvial5%

Tropical Horticulture - Texas A&M University Structure of Tropical Soils VolcanicBest soil structure Oxisols Alfisols Ultisols VertisolsWorst soil structure

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