B-Dry Climates

Introduction to Dry Climates (B-type)

When we talk about Köppen’s classification, the letter B is reserved for Dry climates. Here, the most important feature is not temperature, but water balance.
👉 The defining criterion is:

• Evaporation > Precipitation

So, even if rainfall occurs, it is so little compared to evaporation that the land remains arid.

Under this category, we find two broad landscapes:

1. Grasslands → subdivided into:
   • BSh: Subtropical Savanna grasslands
   • BSk: Temperate Steppe grasslands
2. Deserts → subdivided into:
   • BWh: Hot deserts (low latitude)
   • BWk: Temperate deserts (high latitude)

Hot Desert Climate (BWh)

Location

• Found on the western coasts of continents between 15°–30° latitude N & S.
• Why western sides? Because here, offshore trade winds + cold ocean currents + subtropical high pressure zones combine to suppress rainfall.

That’s why they are also called Trade Wind Deserts.

Examples

• Africa: Sahara, Kalahari, Namib
• Asia: Arabian Desert, Iranian Desert, Thar
• Australia: Great Australian Desert
• North America: Mojave, Sonoran, Mexican Deserts
• South America: Atacama Desert (driest on Earth, <2 cm rainfall annually)

👉 The Atacama is special because:

• Andes create a rain-shadow
• Offshore cold Peru Current cools the air
• Trade winds divert away moisture
• Westerlies remain south of Tropic of Capricorn

Mid-Latitude Desert Climate (BWk)

These are temperate deserts, different from hot deserts in both latitude and cause.

Why are they dry?

1. Continentality → Far away from seas, cut off from moist winds (e.g. Gobi Desert).
2. Rain-shadow effect → High mountains block winds (e.g. Patagonian Desert behind Andes).

Examples

• Asia: Ladakh, Gobi, TaklAmakan, Kyzylkum, Karakum
• America: Great Basin Desert, Patagonian Desert

Desert Climate

Rainfall in Deserts

• Common rule: <25 cm annually
• Occurs mostly in violent thunderstorms, often leading to flash floods.
• Hence, deserts are not only dry but also unpredictable.

Temperature in Hot Deserts

• No cold season → Summers average above 30°C
• Death Valley (USA) holds the record: 56.7°C (1913)
• Diurnal range is very high (14–25°C).
  • Day: clear skies + intense insolation = very hot
  • Night: rapid radiation cooling = sudden drop, even frost in winter nights.

👉 Coastal deserts (like Atacama, Namib) are cooler because of cold currents. Interiors, however, are extreme.

Climate in Mid-Latitude Deserts

• Winters are severe & snowy (due to continental location + altitude).
• Annual range of temperature is much higher than hot deserts.
• In spring, when snow melts, floods are common in many basins.

Desert Vegetation

Vegetation here is xerophytic (drought-resistant).

• Cacti, thorny bushes, wiry grasses, dwarf acacias dominate.
• Trees only near water (e.g. date palms in oases).
• Adaptations:
  • Long roots (to tap groundwater)
  • Reduced leaves → leathery, needle-like, hairy (to cut transpiration)
  • Seeds with thick coats → remain dormant for years until rain comes.
• Soils: low humus, saline, often forming salt pans due to evaporation.

Life in Deserts

Despite being harsh, humans have adapted.

(i) Nomadic Tribes

• Bedouins (Arabia), Tuaregs (Sahara), Mongols (Gobi) → Herdsmen
• Bushmen (Kalahari), Bindibu (Australia) → Primitive hunters

(ii) Settled Cultivators

• River-fed agriculture: Nile (Egypt), Indus (Pakistan), Tigris-Euphrates (Iraq), Colorado (USA)
• Oases cultivation: Date palm is most important crop; also wheat, barley, cotton, sugarcane.
• Example: Tafilalet Oasis (Morocco) covers 7,500 km².

(iii) Mining Settlers

• Australia: Gold (Kalgoorlie, Coolgardie)
• Kalahari: Diamonds, copper
• Atacama (Chile): Sodium nitrate (fertiliser) + copper (Chuquicamata = world’s largest copper town)
• North America: Silver (Mexico), Uranium (Utah), Copper (Nevada)
• Sahara & Arabia: Oil → completely transformed lifestyle and economy

Conclusion

Dry climates may look barren, but they are dynamic ecological and human landscapes.

• Grasslands → grazing economy and fertile black soils (in steppes)
• Deserts → challenges of survival, but also rich in minerals, oil, and culture.

👉 For UPSC, always remember:

• Causes of aridity (trade winds, continentality, rain-shadow, cold currents).
• Adaptations of vegetation & humans.
• Economic significance: agriculture (oases, irrigation), mining, oil.

Steppe / Temperate Grassland (BSk) Climate

Distribution

• Found mainly in the interiors of continents, in the belt of Westerlies.
• Many steppe regions exist due to the rain-shadow effect:
  • Windward side → good rainfall
  • Leeward side → dry grasslands or deserts.
• Practically treeless because:
  • Continentality → too far from seas, no moisture supply.
  • Rain shadow → blocked from rain-bearing winds.

Regional Names

• Steppe → From Black Sea to Altai Mountains (Central Asia)
• Pustaz → Hungary and surrounding regions
• Prairies → North America (Rockies to Great Lakes)
• Pampas → Argentina, Uruguay (rain-shadow of Andes)
• Velds → South Africa
  • Bush-veld → tropical side (north)
  • High-veld → temperate side (south)
• Downs → Australia (Murray–Darling Basin)
• Canterbury → New Zealand (rain shadow of Southern Alps)

Climate

(i) Temperature

• Continental climate → extreme variations.
• Summers: hot, 18–20°C
• Winters: cold, snowy
• In Southern Hemisphere → extremes are less severe (landmass is narrow, surrounded by oceans).

(ii) Precipitation

• Average: ~45 cm annually (range: 25–75 cm)
• If <25 cm → it becomes desert climate.
• More rainfall in Southern Hemisphere due to maritime influence.
• Peak rainfall: June–July (late spring / early summer).
• Winters: ~2.5 cm precipitation (occasional depressions of Westerlies, often as snow).

Natural Vegetation

(i) Grasses

• The main vegetation → short nutritious grasses.
• Difference from tropical savanna:
  • Savanna = tall grasses + scattered trees
  • Steppe = treeless, short, tufted grasses
• Examples:
  • Chernozem (black soil areas of Ukraine) → thick, tall, rich grasses (ideal for wheat).
  • High Plains of USA, Central Asia → shorter, wiry, sparse grasses (less suitable for farming, used for ranching).

(ii) Trees

• Almost absent, except in wooded steppes towards higher rainfall zones.
• In cultivated regions (e.g. Prairies), settlers plant rows of trees around farms as windbreaks.

(iii) Animals

• Not much diversity (unlike tropical savannas).
• Horses are typical of Asiatic Steppes.

Economic Development of Steppes

(i) Wheat & Maize Cultivation

• Called the “Granaries of the World” → Prairies, Pampas, Ukraine, Downs.
• Wheat is dominant; maize also grown in warmer/wetter zones.
• Level land + fertile soils = ideal for mechanised farming.

(ii) Ranching

• Natural grasses replaced with alfalfa (lucerne) → nutrient-rich fodder.
• Pampas of Argentina → global centre for cattle ranching.

(iii) Nomadic Herding (Traditional)

• Earlier, tribes like Kirghiz, Kazakhs in Asian Steppes practiced migratory herding.
• Now replaced by collective farms and settled agriculture under state control (esp. in Central Asia).

(iv) Extensive Mechanised Farming

• The grasslands are flat, fertile, easy to plough → perfect for large-scale mechanised farming.
• Regions: Prairies, Pampas, Ukrainian Steppes, Downs (Australia).

(v) Pastoral Farming

• Ideal for cattle and sheep rearing.
• With refrigerated shipping (19th century), exports of beef, mutton, wool became global.
• Dairy industry also developed (milk, butter, cheese, hides).

Grasslands: Regional Specialisation

Grassland Region	Major Economic Activities
Prairies (N. America)	Wheat granaries, extensive ranching
Pustaz (Hungary, E. Europe)	Wheat (black soil), sugar beet cultivation
Pampas (Argentina, Uruguay)	Alfalfa, ranching, dairy, wheat, beef export
Downs (Australia) & Canterbury (NZ)	Sheep & cattle rearing, merino wool
Velds (South Africa)	Maize farms, sheep & cattle rearing

Key Takeaway for UPSC

• BSk = Steppe = Temperate Grasslands
• Treeless, short nutritious grasses, fertile soils → wheatlands of the world.
• Economically most important grasslands → provide food (wheat, maize), meat, dairy, wool.
• Difference from Savanna: no tall grass/trees, less biodiversity, more suited for mechanised farming.

👉 So, deserts (BW) are “lands of scarcity,” while steppes (BSk) are “lands of plenty.” Both belong to dry climates, but one is barren and challenging, while the other has become the breadbasket of the world.