2.1.1 tropical climates

What is climate?

Average atmospheric conditions, especially temperature and precipitation, usually measured over a 30-year period.

What is climate variability?

Variations in the mean climate, extremes and other statistics over spatial and temporal scales beyond individual weather events.

What is a climate zone?

An area with broadly similar weather statistics, especially temperature and precipitation.

What are the tropics?

A low-latitude climatic region characterised by high temperatures and a radiative surplus.

Where is the fluctuating boundary of the tropics?

Approximately 30-35° N/S.

What are the 5 tropical/dry climates you need to know?

Af — Tropical Rainforest

Am — Tropical Monsoon

Aw — Tropical Savanna

BSh — Subtropical Steppe

BWh — Subtropical Desert

What defines an A (Tropical) climate?

Mean temperature of every month ≥18°C.

What defines a B (Dry) climate?

Potential evaporation exceeds precipitation.

Where is Af (Tropical Rainforest) mainly found?

Along the Equator, extending roughly 10-15° N/S.

Give an Af example.

Singapore.

What is Af's mean monthly temperature?

Approximately 26-30°C throughout the year.

What is Af's annual temperature range?

<3°C, very small.

Why is Af warm throughout the year?

Consistently high solar radiation at low latitudes.

Why does Af have a small annual temperature range?

Little seasonal variation in solar angle and daylength.

How much annual rainfall does Af receive?

Usually >2,000 mm.

Does Af have a dry season?

No distinct wet or dry season.

What is the main rainfall type in Af?

Convectional rainfall.

Explain convectional rainfall in Af.

Strong solar heating → warm moist air rises → adiabatic cooling → condensation → cumulonimbus clouds → intense rainfall.

How does the ITCZ increase Af rainfall?

Convergence and uplift at the ITCZ promote condensation and heavy rainfall.

How long is Af under ITCZ influence?

Approximately 12 months/year.

Where is Am (Tropical Monsoon) mainly found?

South and Southeast Asia, approximately 5-25° N/S.

Give an Am example.

Chittagong, Bangladesh.

What is Am's mean monthly temperature?

Approximately 26-30°C.

What is Am's annual temperature range?

Approximately 3-6°C.

How much annual rainfall does Am receive?

Usually >2,000 mm.

What distinguishes Am rainfall from Af?

Am has much stronger rainfall seasonality, with a wet season and short dry season.

What causes Am's wet season?

Seasonal monsoon winds transport moist oceanic air inland + ITCZ convergence.

What causes Am's dry season?

Winds blow from the continental interior towards the ITCZ, bringing drier air.

How can relief increase Am rainfall?

Mountains force moist air upwards → orographic uplift → cooling, condensation and heavy rainfall.

How long does the ITCZ influence Am?

Approximately 6-12 months/year.

Where is Aw (Tropical Savanna) located relative to Af?

Poleward of Af, usually further inland (away from coast).

What is Aw's approximate latitude?

5-30° N/S.

Give an Aw example.

Arusha, Tanzania.

What is Aw's annual temperature range?

Approximately 3-10°C.

How much annual rainfall does Aw receive?

Approximately 500-1,500 mm.

What is the defining rainfall characteristic of Aw?

Distinct wet and dry seasons.

What causes Aw's wet season?

ITCZ moves overhead → convergence and uplift → heavy rainfall.

What causes Aw's dry season?

ITCZ migrates away → STHP dominates → subsiding stable air → suppressed rainfall.

What happens to Aw rainfall further from the Equator?

Rainfall generally becomes lower, less reliable and more variable.

How long does the ITCZ influence Aw?

<6 months.

Where is BSh (Subtropical Steppe) generally located?

Transitional zone between Aw and BWh, often around desert margins.

Give a BSh example.

Walgett, Australia.

How much annual rainfall does BSh receive?

Approximately 250-500 mm.

What is BSh rainfall like?

Low, highly variable and unreliable, with distinct wet/dry seasons.

What is the main cause of BSh dryness?

Subsiding air associated with the STHP.

Why does BSh have a large diurnal temperature range?

Low humidity + little cloud cover → strong daytime heating and rapid nighttime radiative cooling.

Where is BWh (Subtropical Desert) mainly found?

Approximately 15-25° N/S, commonly on western continental margins.

Give a BWh example.

Riyadh, Saudi Arabia.

How much annual rainfall does BWh receive?

Usually <250 mm.

What is BWh rainfall like?

Very low, irregular and unreliable.

What is the main cause of BWh aridity?

STHP → subsiding air → adiabatic warming → condensation/cloud formation suppressed → little rainfall.

What 3 factors cause desert aridity?

STHP

Continentality

Cold ocean currents

How does continentality cause desert aridity?

Continental interiors are far from major moisture sources.

How do cold ocean currents cause desert aridity?

They cool and stabilise air, suppressing convection and rainfall.

Why is BWh's diurnal temperature range very large?

Very low humidity/cloud cover → intense daytime heating + rapid nighttime terrestrial radiation loss.