Deserts

Describe the distribution of deserts?

• on the tropics - around 30 degrees latitude in both hemispheres

• Africa, Asia, Australia, South America, North America

• e.g Sahara in north Africa

Describe the climate of deserts?

• arid (extremely dry)

• hot during the day) and often below freezing at night

• less than 10 inches of rainfall per year

• NASA says average day temp is 38 degrees

what is the soil like in deserts?

• saline (salty) — evaporation of moisture draws salts to earth surface

• infertile — hard for growth of vegetation

• limited leafy vegetation — leaves don’t really fall/get decomposed with their nutrients being absorbed back into the soil

• sandy/stony

why are deserts located where they are?

• air is sinking —- very little evaporation — little rain

Wind direction?

• if wind blows mainly over land, then the air will be dry so there will be no rain, forming a desert in that area

• e.g Gobi

Atmospheric pressure?

• high pressure = warm air is sinking and there’s no evaporation so clouds can’t form

Cloud cover?

• no/very few clouds

• no rainfall so dry

• no shade from sun so hot

• no moisture = no condensation, so no clouds

Diurnal temperature change?

lack of clouds/cloud coverage means that there are:

• high day temps

• low night time temps

Rainshadow?

• warm moist air is forced up and over mountains

• cools and rapidly condenses on mountains

• air descends the the other side and creates a dry area or "shadow" on the leeward side

Ocean currents?

• some areas (s. America) have cold offshore currents that chill the winds so they don’t evaporate much water vapour

• any moisture they do hold falls as showers or forms fog, meaning its dry winds blow over desert

how do plant roots adapt?

• very deep into ground or spread broadly around plant

• allows the plant to capture maximum water when it does rain

leaves?

• have small spines instead of leaves

• gives the minimum possible surface area so water can be preserved by plant instead of being lost by evaporation/transpiration

dormant seeds?

• some plants only reproduce when it rains — if they tried to when it didn’t the seeds would die

• dormant throughout year and germinate when rain is present

water storage mechanisms?

• succulent plants have thickened area that can be used to store water

• plants need this area as there is so little rainfall

why do some plants in desert have rapid life cycle?

• to ensure water supply doesn’t run out

• this means the plant is ephemeral

• e.g desert dandelion

how is a cactus adapted to survive in the desert?

• spines instead of leaves —> minimise surface area/ reduce water loss/protection from being eaten by animals

• widespread root systems close to the surface that collect water from large area

How are coyotes adapted to live in the desert?

• live in us deserts

• nocturnal : means they do not have to move/expend much energy during the hottest part of the day and can shelter in shade

How are camels adapted?

• store water for long period of time in their bloodstream

• humps store fat so they have constant access to a food source/can be turned into water

• feet have wide surface area: don’t get stuck in soft sand

• long eyelashes

How are jackrabbits and fennec foxes adapted?

• large ears - high surface area to volume ratio, so can dissipate heat more easily

what are the opportunities for development in the Thar desert?

• extracting minerals like gypsum

• Desert safaris for tourists

• Production of energy

• Farming

• irrigation

Energy production?

• rich energy source

• coal → extensive lignite coal deposits in parts of desert

• oil → large oil field discovered in Barmer district of the desert → transformed economy

• wind → Jaisalmer wind park focuses on renewabale wind power and is biggest wind farm in India

• solar → sunny cloudless skies are ideal conditions for solar power

Mineral extraction?

• exported throughout india and globally

• gypsum: plaster/cement for construction industry

• feldspar: used to make ceramic

• phospherite: making fertiliser

• valuable stone reserves → Jaisalmer’s sanu limestone is the main source India’s steel industry

Tourism?

• 10,000 visit each year

• safaris on camels

• annual festival held in winter → local people provide food, accommodation & look after camels

Farming?

• most people living in desert are involved in substinence farming

• graze animals to survive hot/dry conditions

• the Indira Gandhi canal has enabled the irrigation of 3500k㎡ of land for the commercial production of wheat, cotton and maize

What are the challenges in the Thar desert?

• accessibility

• extreme temperatures

• poor water supply

Accessibility?

• roads covered with sand and crack because of heat makes it difficult to travel over

• tarmac can melt during day

• vast barren areas limit road network

Extreme temperatures?

• high average temperature

• water evaporates quickly

• hard conditions to work in, especially for farmers

water supply?

• low rainfall and high rates of evaporation lead to poor water security

• high rates of evaporation are caused by high temperatures and strong winds

why is the Indira Ghandi Canal important?

• 650km

• provides irrigation and drinking water

what is desertification?

• where land is gradually turned into desert

• mostly occurs on ecologically fragile borders of existing deserts

• a result of natural and human events → droughts and mismanagement

• affects poor and rich countries

• threatens one billion people in areas at risk