Unit 17
TROPICAL (A) AND ARID (B) CLIMATES
Unit OverviewAs a continuation of Unit 16, this unit examines closely the tropical (A) and arid (B) climates of the Köppen climate classification system. The main sections are:
- The major tropical (A) climates
- The major arid (B) climates
The A climates are located at low latitudes, and typically straddle the equator. These climates are controlled by the inter-tropical convergence zone (ITCZ). The B climates are located in many places across the globe. These climates are defined by their relative aridity; they are associated with under subtropical high-pressure cells, extreme continentality, and the leeward side of mountains. The temperature and precipitation characteristics of the A and B as well as of the other climate types can be examined visually using a climograph. If a meteorological station has a minimum of 30 years of valid temperature and precipitation measurements, then the average monthly temperatures and precipitation totals can be plotted as a graph (temperature as a line and precipitation as a bar). Some major environmental problems associated with the A and B climates, respectively, are deforestation and desertification.
Unit Objectives
- To expand the discussion of tropical (A) and arid (B) climates using climographs developed for actual weather stations
- To highlight climate-related environmental problems within tropical and arid climate zones
- To examine the causes and consequences of tropical deforestation and desertification
Glossary of Key Terms
Arid climate | Dry climate where potential evaporation always exceeds the moisture supplied by precipitation; found in areas dominated by the subtropical high pressure cells, in the interiors of continents far from oceanic moisture sources, and in conjunction with rain-shadow zones downwind from certain mountain ranges. |
Climograph | A graph that simultaneously displays, for a given location, its key climatic variables of average temperature and precipitation, showing how they change monthly throughout the year. |
Desertification | The process of desert expansion into neighboring steppelands as a result of human degradation of fragile semiarid environments. |
Tropical climate | Climate dominated by warmth (due to low-latitude location) and moisture (from the rains of the Inter-Tropical Convergence Zone); contained within a continuous east-west belt astride the Equator, varying in latitutde from 30 to 50 degrees wide. |
Tropical deforestation | The clearing and destruction of tropical rainforests to make way for expanding settlement frontiers and the exploitation of new economic opportunities. |
Unit Outline
- The major tropical (A) climates
- The tropical rainforest climate (At)
- located close to Equator
- high temperatures and large amounts of rainfall
- convectional thunderstorms
- dense canopy of tropical forest
- The monsoon rainforest climate (Am)
- located on tropical coasts, often near highlands
- distinct short dry season in winter
- evergreens and some grasslands
- The savanna climate (Aw)
- located in transitional area between subtropical highs and equatorial low pressure belts
- extended dry season in winter
- tall grasses, individual trees, thorny bushes
- The tropical rainforest climate (At)
- The major arid (B) climates
- The desert (BW) climate
- located near 30 degrees north and south at the subtropical highs
- minimal precipitation
- sparse vegetation
- The steppe (BS) climate
- located on the edges of the most arid (BW) deserts
- semiarid, rainfall varying with latitude (more in lower latitudes)
- short-grass prairie vegetation
- Human activities in B climates
- Virgin and Idle Lands Program (former Soviet Union)
- Great Plains droughts
- Nile Valley
- desertification
- The desert (BW) climate
Review Questions
- Compare and contrast the general types of plant life found in A and B climate zones.
- What is a climograph?