The characteristics of extreme environments practice questions.

A place records 180 mm of rainfall a year, a daytime maximum above 40 °C in summer and a night-time drop of more than 20 °C. Which characteristic explains the very large diurnal temperature range?

• Cloudless skies and dry air allow rapid radiative loss after sunset
• The high daytime temperature prevents any heat being stored in the ground
• Low rainfall raises the specific heat capacity of the surface material
• Strong winds at night transport cold air from higher latitudes

Answer: Cloudless skies and dry air allow rapid radiative loss after sunset

Water vapour and cloud are what trap outgoing longwave radiation; with almost neither, the surface radiates heat straight to space overnight. Aridity therefore explains both the heat and the cold, which is why the diurnal range in a desert exceeds the annual range in many humid places.

The Atacama and Namib deserts both lie on western coasts in the subtropics. Which combination of controls explains their extreme aridity?

• Subtropical high pressure with subsidence, plus a cold offshore current
• Continentality and distance from any moisture source
• A rain shadow behind a mountain range on the coast itself
• Permanently frozen ground preventing evaporation from the surface

Answer: Subtropical high pressure with subsidence, plus a cold offshore current

Descending air at about 20-30 degrees warms and dries, suppressing convection, and a cold current chills the air above it so that moisture condenses as coastal fog rather than falling inland as rain. Continentality explains interior deserts such as the Gobi, and although the Andes add a rain shadow in the Atacama, the Namib has no such barrier, so only subsidence plus a cold current is common to both.

Ground that remains at or below 0 °C for at least two consecutive years is a defining feature of periglacial environments. Which term describes it?

• Permafrost
• The active layer
• A glacier
• Tundra vegetation

Answer: Permafrost

Permafrost is defined by temperature and duration, not by ice content, and it is overlain by the active layer that thaws each summer. The distinction matters because it is the active layer, not the permafrost, that determines what can grow and what can be built on.

Why does settlement in extreme environments form isolated clusters rather than an even spread?

• They cluster at a single exploitable resource or transport node
• Extreme environments have uniform conditions throughout
• National governments prohibit dispersed rural settlement there
• Water is equally available across the whole environment

Answer: They cluster at a single exploitable resource or transport node

Where the environment offers almost nothing, settlement follows a specific asset - an oasis, an ore body, a port, a research station - so the pattern is point-like rather than dispersed. Norilsk, Yellowknife and the Atacama mining towns all show it.

The Atacama Desert lies on the coast at about 23°S; the Gobi Desert lies deep in the interior of Asia at about 43°N. Both are arid, but only the Gobi has winter months with mean temperatures well below 0 °C. Which control best explains that contrast in temperature?

• The cold ocean current flowing along the coast beside the Atacama
• The descending limb of the Hadley cell over the subtropics
• The rain shadow cast by a high mountain barrier upwind
• The Gobi's higher latitude and its distance from any ocean

Answer: The Gobi's higher latitude and its distance from any ocean

The controls that make a place dry and the controls that make it cold are separate questions: a cold current, subtropical subsidence and a rain shadow all reduce rainfall, but only latitude and continentality set the winter temperature. Ocean water beside the Atacama keeps its winters mild.

Drylands are classified using the aridity index, the ratio of mean annual precipitation to potential evapotranspiration (P/PET). A station records an aridity index of 0.15. Which dryland class does that value place it in?

• Hyper-arid
• Arid
• Semi-arid
• Dry sub-humid

Answer: Arid

The conventional boundaries are hyper-arid below 0.05, arid 0.05-0.20, semi-arid 0.20-0.50 and dry sub-humid 0.50-0.65, so 0.15 is arid. The index matters because it compares supply with demand, whereas a rainfall total on its own says nothing about evaporative loss.