SAJC Cluster 2 Lecture 1 Notes (Climate Zones in The Tropics)

St Andrew’s Junior College H2 Cluster 2: Tropical Environments H2_Cluster 2 Lecture 1_2024/pg1 Lecture 1 Tropical Climates (I): Climatic Zones in the Tropics KEY QUESTION: What are the similarities and differences in the temperature and rainfall patterns in the tropics? With the completion of this lecture, attached readings and tutorial, you should be able to understand that: • Locations in the tropics are classified into climatic zones according to their temperature and rainfall characteristics. • High temperatures are the key distinguishing characteristics of the tropics. • There are variations in the amount of rainfall between the humid and arid tropics. • There are seasonal variations in rainfall patterns in parts of the tropics. Lecture Outline 1.1 Introduction: Where is “the Tropics”? 1.2 The Tropics and the Köppen-Geiger Climate Classification System 1.3 Humid Tropical Climates (A Climates) 1.3.1 Tropical Rainforest Climate (Af) 1.3.2 Tropical Monsoon Climate (Am) 1.3.3 Tropical Savanna Climate (Aw) 1.4 Arid Tropical Climates (B Climates) 1.4.1 Tropical Desert Climate (BWh) 1.4.2 Subtropical Steppe Climate (BSh) 1.5 Summary Box 1: The Shifting Location of the Overhead Sun Relative to the Earth’s Surface Box 2: Reading climographs The Tropics: A climatic region of radiation surplus delimited by boundaries fluctuating between 30° and 35° latitude, north and south of the equator.

St Andrew’s Junior College H2 Cluster 2: Tropical Environments H2_Cluster 2 Lecture 1_2024/pg2 1.1 Introduction: Where is “the Tropics”? • The Tropics may be described as… A climatic region of solar radiation surplus delimited by boundaries fluctuating between 30 ˚ and 35˚ north and south latitudes. Common to all areas in this region (at sea level) is high temperature. Significant variations in the amount and pattern of rainfall differentiate these areas into different tropical climate zones, primarily the humid tropics and the arid tropics. 1.2 The Tropics and the Köppen-Geiger Climate Classification System • A climatic zone is an area designated by broadly similar weather statistics, especially temperature and precipitation. For our purpose, the Köppen-Geiger climate classification system will serve as our reference. • The Köppen-Geiger system is by far the most widely used climatic classification system. It uses a numerical basis of classification (either average temperatures or average amounts of precipitation), and zone boundaries are determined by vegetation patterns. • As Fig. 1 shows, the world’s climate can be broadly classified into are five major climatic zones (A through E) plus a sixth zone (H) called highland climates. Tropical Climates • Tropical climates are classified in Humid Tropics (or A climates) and Arid Tropics (or B climates) (see Table 1). Table 1: The Sub-Types of Tropical Climatic Zones Type Sub-type Letter Code Characteristics A climates or Humid Tropics Tropical rainforest Af No dry season, Wet throughout the year Tropical monsoon Am Short dry season, Long wet summer season Tropical savanna Aw Long dry winter season, Short wet season B climates or Arid Tropics Subtropical steppe BSh Low-latitude semi dry throughout the year Tropical desert BWh Low-latitude dry throughout the year • Mean annual temperature is high everywhere in the tropics (both humid and arid regions). This is the key characteristic that distinguishes the tropics from other climatic zones in the world. o For example : Places in different latitudes within the tropic experiences high mean annual temperature as these are all located in the low latitudes. Mean annual temperature of Singapore (Af) (1°N) is 26.5°C, Kolkata (Am)(23°N) is 26.8°C, Cairo (BWh)(30°N) is 23.1°C. • However, annual temperature range varies over time and space. • In case of rainfall characteristics, there is variations in amount and pattern of rainfall in the tropics.

St Andrew’s Junior College H2 Cluster 2: Tropical Environments H2_Cluster 2 Lecture 1_2024/pg3 Fig. 1 This world map of climate patterns is largely based on Köppen-Geiger system of climate classification

St Andrew’s Junior College H2 Cluster 2: Tropical Environments H2_Cluster 2 Lecture 1_2024/pg4 1.3 Humid Tropical Climates (A climates) • The humid tropical climates occupy almost all the land area of Earth within some 15 -20° north and south of the equator. • This globe-girdling belt of A climates is interrupted slightly here and there by mountains or small regions of aridity, but it dominates the equatorial regions and extends to the 25° latitude in some windward coastal lowlands (see Fig. 2). General Characteristics of A Climates • The A climates are characterised by high temperatures throughout the year, as is to be expected from their near-equatorial location. (See Lecture 2) o The sun is high i n the sky every day of the year . These are climates of perpetual warmth (although they do not experience the world’s highest temperatures). o The fundamental character of the A climates, then, is moulded by their latitudinal location. • The second typifying characteristic of the tropical climates is of course the prevalence of moisture. (See also Lecture 2). Much of the A climates is among the wettest in the world. o Warm, moist, unstable air masses frequent the oceans of these latitudes, and the ITCZ is in the A climate for much of the year. o Moreover, onshore winds and thermal convection are common phenomena. o Thus the A climate has not only abundant sources of moisture but also abundant mechanisms for uplift. High humidity and considerable rainfall are expectable results. • The humid tropical climates are classified into three types on the basis of annual rainfall. We shall elaborate these in subsequent sub-sections. o The tropical rainforest climate (Af) has abundant rainfall throughout the year ranging between 1500 mm and 2500 mm annually. o The tropical monsoon climate (Am) has a short dry winter season and a long rainy or wet summer season with rainfall ranging between 2500 mm and 5000 mm annually. o The tropical savanna climate (Aw) is characterised by a distinct short rainy or wet summer season and a long dry winter season with rainfall ranging between 90 0 m m and 180 0 m m annually. Fig. 2 [Type a quote from the docume nt or the summar y of an interesti ng point. You can position the text box anywhe re in the docume nt. Use the Drawin g Tools tab to change the formatti ng of the pull

St Andrew’s Junior College H2 Cluster 2: Tropical Environments H2_Cluster 2 Lecture 1_2024/pg5 1.3.1 Tropical Rainforest Climate (Af) Climograph example Fig. 3 Location Climates of the Af type characteristically occur in an east -west sprawl close to the equator, lying 5-10˚ N and S of the equator (See Fig. 2). The 3 largest tropical rainforest climates are found in: o The Amazon Basin of South America o The northern Zaire (Congo) basin of western equatorial Africa o Southeast Asia (includes Singapore, Malaysia and Indonesia) Characteristics of temperature pattern General temperature pattern: Tropical rainforest climate (Af) is known for uniformly high mean annual temperature. It is hot all the year round with an mean sea-level monthly temperature of about 27˚C. This is a seaso