10.1 hot arid and semi arid climate

Question 1

define aridity

Answer 1

definition based on water availability with focus on difference between ppt, evap, transpiration

Question 2

where are arid areas found?

Answer 2

at the tropics (30/60), along cold ocean currents, western side of continents, interior of continents/landmasses, in the lee of mountains

Question 3

explain how the sub-tropical high pressure causes aridity

Answer 3

• global atmospheric circulation: subsidence of Hadley cell:
  1. equatorial air warms, rises, cools, loosing water vapour as rainfall
  2. Moisture depleted air moves away and up from equator
  3. sinks back down at 30 latitude
  4. belts of aridity form beneath the cold dry descending, high pressure air masses of the Hadley cell
  5. as air descends it prevents rising air from reaching sufficient height for condensation and precipitation
  6. subsided air spreads out thereby preventing incursion of warm maritime air into region

Question 4

explain how continentality causes aridity

Answer 4

• characterised by small area of aridity and extensive area of semi-aridity
• the further you are from the ocean the less available water is to evaporate into the atmosphere, limiting the amount of water carried by winds
• land takes less heat energy to heat
• water bodies do not influence T ?

Question 5

explain how the rain shadow effect causes aridity

Answer 5

• trade winds meet mountain barriers, air is forced to rise
• adiabatic cooling
• orographic rainfall forms on windward side
• dehydrated air descends on leeward side

Question 6

explain how cold ocean currents causes aridity?

Answer 6

• cold water decreases the temperature of the overlying air mass and so reduces amount of water it can hold
  -limits amount of condensation into air, causing low sea surface evaporation, high atmospheric humidity
  -low rainfall, precipitation mainly in the form of fog and dew and a small temperature range
  -several deserts lie of the western coasts of continents where there is an upwelling of cold water due to circulation of wind currents that travel from high latitude to low towards the equator
  -water falls before reaching land which therefore becomes arid

Question 7

rainfall as a key feature of arid environments

Answer 7

• little rainfall
• high variability
• storms can happen and still be low intensity
• fog important in coastal deserts providing just enough moisture to keep flora and fauna alive

Question 8

temperature as a key feature of arid environments

Answer 8

• can vary considerably
• continental interior: large diurnal T, frost is possible too
• coastal deserts usually have fairly low seasonal and diurnal T range

Question 9

wind as a key feature of arid environments

Answer 9

-erosional agent
-able to build due to lack of obstacles and friction

Question 10

semi arid poleward of hot deserts (BSHs)

Answer 10

• summer very hot and dry
• winter has occasional rain, especially in mid latitudes
• high variability: sometimes years of drought/storms
  -usually coarse grass and drought resistant plants

Question 11

semi-arid outer tropical climate (BSHw)

Answer 11

• bordering deserts
• long, dry winters
• brief erratic rainfall due to the ITCZ
• not conductive to plant growth due to hot T and rapid evaporation
• years of average rainfall followed by years of drought
• Sahel region

Question 12

hot deserts (BWh)

Answer 12

• descending air affects the very dry western part of landmasses
• prevents convective updraughts
• humidity is low
  cumulonimbus clouds form and can result in flash flooding and sheetwash
• daytime T during summer may reach 50-55C and fall to 20-25C during the night
• during winter daytime Ts are 15-20 and may be cold enough to hit dew point

Question 13

Death Valley : Rain shadow example

Answer 13

• South-eastern California
• bounded on the west by the Panamint Range: elevations average 2,000
• rain shadow effect
• in summer the floor of Death Valley often exceeds 49 °C , winter minimum barely falls below freezing point,lowest of 9 °C
• During a 50-year period in the 20th century, the average annual rainfall at Furnace Creek was only 42.2 mm

Question 14

Kalahari Desert: Sub-tropical example

Answer 14

• South Africa, 30 latitude
• region is dominated by the southern hemisphere descending limb of the Hadley cell
• Area has no drainage system: evaporation twice the rate of precipitation
• Great ranges in both diurnal and seasonal temperatures (due to high altitude and clear, dry air allowing strong insolational heating in daytime and great radiational heat loss at night)
• shade temperatures often reach 46 °C on summer days but drop to 27 °C on the same nights; temperatures on winter nights commonly drop to freezing and may go as low as 12 °C

Question 15

Gobi Desert: continentality example

Answer 15

• Cuts across Mongolia and Northern China, hundreds of kilometres from the ocean
• Continentality
• The annual total precipitation 50 mm in the west
• -38°C at its coldest and +42°C at its warmest in summer

Question 16

Atacama Desert: cold ocean currents example

Answer 16

• northern Chile
• the Peru Current, is a cold, low-salinity ocean current that flows north along the western coast of South America
• Coastal mountain range interjects between warm currents coming from PO
• average rainfall is about 15 mm per year
• summer months the average temperatures are around 27°C during the day and 16°C at night