TMJC 2025 JC1H2 C2 Lecture 1 Tropical Climate Classification

Higher 2 (9173) Tropical Environments TMJC C2 Lecture 1 Characteristics of Tropical Climates 2025 Page 1 of 8 LECTURE OBJECTIVES 1. Discuss the dynamism of natural environments in the tropics • Distinguish tropical climates based on the Koppen-Geiger climate classification system Introduction Climate is defined as the average weather conditions of a place over a long period of time, usually 30 years or more. It should not be confused with the weather, which is defined as the condition of the atmosphere at a particular time, or over a short period of time (hours or days). Most of the atmosphere, and therefore our climate and weather, is concentrated within the troposphere, within 16km of the Earth’s surface at the Equator and 8km at the Poles. (Don’t need to Memorise!) Before we begin: Recall the difference between the earth’s revolution and rotation. \

Page 2 of 8 (A) WHAT IS THE TROPICS? 1. The tropics is defined as a climatic region of radiation surplus 1 located between 30-35 degrees north and south of the equator (Fig. 1). a. Due to radiation surplus, areas within the tropics have high average annual temperatures of at least 18oC. There is however, some variation in the annual temperature range and diurnal temperature range within the tropics. b. Unlike temperature , precipitation patterns within the tropics differ widely , ranging from the: i. Humid tropics: Tropical Rainforest (Af) climate. ii. Seasonally Humid tropics: Tropical M onsoon (Am) climate and Tropical Savanna (Aw) climate. iii. Arid tropics: Sub-tropical steppe (BSh) climate and Tropical desert climate (BWh). Fig. 1: Areas defined as ‘tropics’ (B) WHAT ARE VARIOUS TYPES OF CLIMATES PRESENT IN THE TROPICS? 1. For the current A -Level Geography syllabus, we will examine 5 main types of climates present in the tropics, classified according to the Koppen -Geiger climate classification system. They are the: a) Tropical rainforest (Af) climate b) Tropical monsoon (Am) climate c) Tropical savanna (Aw) climate d) Sub-tropical steppe (BSh) climate & e) Tropical desert (BWh) climate 1 Radiation surplus means that the outgoing energy from the Earth (in the form of longwave terrestrial radiation) is smaller than the incoming energy from the sun (in the form of shortwave solar radiation) for the particular area.

Page 3 of 8 (C) WHAT ARE THE FEATURES OF THE TROPICAL RAINFOREST (Af) CLIMATE? 1. Temperature characteristics (Fig. 2): a. Mean annual temperature is high, usually between 26°C to 28°C. b. Seasonality of temperature is absent , with temperatures being constantly high throughout the year. c. Annual temperature range is small, usually less than 3°C. d. Diurnal temperature range is small at around 10°C, with average temperatures of 32°C in the day and 22°C at night. 2. Rainfall characteristics: a. Annual total rainfall is high, at more than 1500mm. b. Seasonality of rainfall is absent, with an even distribution of precipitation for each month at a minimum of 60mm. Rainfall is mainly in the form of convectional rainfall in the late afternoons. Fig. 2: A climograph of a tropical rainforest (Af) climate E.g. Singapore

Page 4 of 8 (D) WHAT ARE THE FEATURES OF THE TROPICAL MONSOON (Am) CLIMATE? 1. Temperature characteristics (Fig. 3): a. Mean annual temperature is high, above 18°C. b. Seasonality of temperature is present , with temperatures being higher during summer, when the sun is more directly overhead. This occurs during the middle of the year (June) in the northern hemisphere and the end of the year (December) in the southern hemisphere. c. Annual temperature range is small, but larger than that of tropical rainforest climate, ranging from 3°C to 6°C. d. Diurnal temperature range is greater than tropical rainforest climate. It is variable depending on season (10 °C - 25°C). It may exceed 25 °C during dry season when cloud cover is absent, but will be lower during wet season when cloud cover is present. 2. Rainfall characteristics: a. Annual total rainfall is high, at more than 1500mm. b. Seasonality of rainfall is present, with a marked short dry season with one or more months receiving less than 60mm. The rainy season is excessively wet, with large amounts of rainfall falling mainly during the wet season. Fig. 3: A climograph of a tropical monsoon (Am) climate e.g Kerala, India

Page 5 of 8 (E) WHAT ARE THE FEATURES OF THE TROPICAL SAVANNA (Aw) CLIMATE? 1. Temperature characteristics (Fig. 4): a. Mean annual temperature is high, above 18°C. c. Seasonality of temperature is present, with temperatures being higher when the hemisphere in which the climate is located in gets more insolation due to the change in position in relation to the overhead sun. Temperature of coolest month is greater than 18°C. b. Annual temperature range is small, but larger than that of tropical rainforest climate and tropical monsoon climate, ranging from 3°C to 10°C. c. Diurnal temperature range is greater than tropical rainforest climate. It is variable depending on season (10 °C - 25°C). It may exceed 25 °C during dry season when cloud cover is absent, but will be lower during wet season when cloud cover is present. 2. Rainfall characteristics: a. Annual total rainfall is moderate, at between 500mm to 1500mm. b. Seasonality of rainfall is present, with monthly precipitation totals dropping below 60mm for four to six months during the dry season. The rainfall mainly falls during the wet season, with heavy convectional rainfall during wet season in summer giving 80% of the total annual rainfall in four or five months. Fig. 4: A climograph of a tropical savanna (Aw) climate E.g. Bangkok, Thailand

Page 6 of 8 (F) WHAT ARE THE FEATURES OF THE SUB-TROPICAL STEPPE (BSh) CLIMATE? 1. Temperature characteristics (Fig. 5): a. Mean annual temperature is high, above 18°C. d. Seasonality of temperature is present, with temperatures being higher during the summer when maximum daytime temperatures can exceed 50°C. The lowest average temperatures occur during winter. Temperature of coolest month is greater than 18°C. b. Annual temperature range is large ranging from 20°C to 30°C. c. Diurnal temperature range is very large, ranging from 20°C to 50°C), due to high daily temperatures which can exceed 40°C and low night -time temperatures which can drop below 0°C. 2. Rainfall characteristics a. Annual total rainfall is very low, but larger than the tropical desert climate, between 250 and 500 mm. b. Seasonality of rainfall is present, with some monthly precipitation totals at above 60mm. Precipitation may occur due to short incursions of the ITCZ or from occasional mid-latitude cyclones. Fig. 5: A climograph of a sub-tropical steppe (BSh) climate (e.g. Dakar, Senegal)

Page 7 of 8 (G) WHAT ARE THE FEATURES OF THE TROPICAL DESERT (BWh) CLIMATE? 1. Temperature characteristics (Fig. 6): a. Mean annual temperature is high, above 18°C. e. Seasonality of temperature is present, with temperatures being higher during the summer when maximum daytime temperatures can exceed 50°C. The lowest average temperatures occur during winter. Temperature of coolest month is greater than 18°C. b. Annual temperature range is large ranging from 20°C to 30°C. c. Diurnal temperature range is very large, ranging from 20°C to 50°C), due to high daily temperatures which can exceed 40°C and low night -time temperatures which can drop below 0°C. 2. Rainfall characteristics: a. Annual total rainfall is very low, at less than 250mm. b. Seasonality of rainfall is absent, with total monthly precipitation below 60mm for all months of the year. Precipitation is irregular and unreliable, usually in the form of convectional rainfall during summer. Fig. 6: A climogra