hot deserts

Question 1

describe the distribution of hot deserts globally:

Answer 1

hot deserts are mainly distributed on and around the tropics of Cancer and Capricorn, and never on the Equator. they’re situated on the majority of continents, especially in North Africa and the West of South America.

Question 2

describe the rain-shadow effect:

Answer 2

moist air arrives from a body of water, and encounters a mountain. the air is forced to rise over the mountain, cool, condense, and form rainclouds. rain falls on the windward side of the mountain, creating a rainforest. the air then continues over to the other, leeward side of the mountain, and sinks. this cold, sinking air creates an area of high pressure, creating cloudless skies and little rain. this is the rain shadow region, where a desert forms.

Question 3

what is the average desert climate throughout the year?

Answer 3

• temperature rises to a peak towards the middle of the year, with lowest average temperatures being 16/17 degrees celsius in december, and highest temperatures being roughly 45 degrees celsius in july.
• rainfall is low all year round, with the highest yearly rainfall occurring in january, at 4.5 mm of rain across the entire month. may and june usually have particularly low rainfall levels, at 0-2 mm of rainfall.

Question 4

how does the Hadley cell influence where hot deserts occur?

Answer 4

• the sun is overhead at the equator and water evaporates. it heats the air, which rises and carries moisture up. it then cools and condenses to form rain. this forms a tropical rainforest.
• the air continues to the north and south, and the dry air begins to sink at the two tropics, creating clear skies and desert conditions. this is where deserts occur, at about 30 degrees north and south of the equator.
• the air then travels back to the equator, and the cycle starts again.

Question 5

what are the physical characteristics of the desert ecosystem?

Answer 5

• lack of vegetation
• poor, dry soil
• clear skies (due to high pressure)
• mountains/flat plains
• hot, has little rain
• extreme temperatures: over 45 degrees celsius during the day, drops to 0 degrees celsius at night.
• less than 250mm of rainfall per year.

Question 6

describe the desert climate:

Answer 6

• a daily diurnal range: hot in the day, cold at night. this is because clear skies during the day mean the sun can heat the surface temperature to over 40 degrees celsius. at night, however, there are no clouds to act like a blanket to keep the heat in, so heat is lost. temperatures drop very low, to even 0 degrees celsius.
• windy with frequent sandstorms as air moves from high to low pressure.
• unreliable rainfall: flash floods can happen as sometimes, the whole year’s rainfall falls in one very heavy storm.
• dry with overall very low rainfall all year: the definition of desert is a place which receives under 250mm of precipitation/per year.

Question 7

how is water accessed in desert areas?

Answer 7

• the Hoover Dam helps store the water of the Colorado River in Lake Mead behind.
• in many desert areas, water is stored in underground rocks called aquifers. it can then be pumped to the surface for use.
• large canals and aqueducts then distribute water to desert areas in Arizona and California.
  > this does mean that water is subject to
  evaporation, however, but the process is
  relatively easier and less expensive.

Question 8

describe desert soil:

Answer 8

• can be either rocky/sandy.
• the soil is exposed to extreme temperatures, and is often partially formed because of the lack of water.
• high evaporation rates mean that salts are drawn to the surface, leaving a white crust. this is called SALINISATION.
• the lack of plants means there’s little organic matter in the soil, so it’s not very fertile.

Question 9

describe some common animal adaptations:

Answer 9

• nocturnal: it’s cooler to hunt at night than during the day.
• live underground: provides shade from the hot midday sun.
• large ears: (e.g. fennec fox). blood flow through the ears will be cooled by the wind through the stretched, taut skin. this blood then re-enters the body and cools the animal internally.
• bushy tails: (e.g. desert ground squirrel). when animals hunt, the tail can act as a parasol, when positioned correctly. this prevents the animal from overheating.

Question 10

describe the adaptations of a camel:

Answer 10

• stretchy nostrils that open and close to keep out the sand.
• a leathery mouth, allowing camels to eat spiky plants (e.g. cacti).
• long eyelashes with multiple layers to keep sand out of their eyes.
• hump on the back to store fats and minerals, which can be broken down into essential nutrients (e.g. water) during droughts, which are common in the desert. water is stored under the belly to keep it cool.
• padded feet protect the feet from sinking into the ground, and to protect it from the heat of the ground.

Question 11

describe the adaptations of meerkats:

Answer 11

• dark patches around the eyes help cut down on the sun’s glare.
• long, horizontal pupils give them a wide range of vision to spot predators more easily.
• thin fur and dark stomach skin help to regulate body temperature.
• a special membrane can cover and protect the eye while burrowing, and close-able ears to prevent sand-intake.

Question 12

describe the adaptations of the desert holly:

Answer 12

• takes salt from the soil and creates a thin white surface coating to reflect the sunlight.
• it’s leaves grow at a 70 degree angle, so that the plant doesn’t receive direct sunlight at midday.
• some have long, shallow roots, which collect water over large areas.

Question 13

describe the adaptations of the saguaro cactus:

Answer 13

• many long but shallow roots to soak up as must water as possible after rainfall.
• thick, waxy skin reflects some of the sun’s heat and reduces moisture loss through transpiration. it also takes up the job of photosynthesis, because of its chlorophyll presence.
• spikes instead of leaves reduce moisture loss (more efficient in heat) and prevent many animals from eating the plant.

Question 14

how can a thick, fleshy body aid some plants?

Answer 14

thick, fleshy bodies (called succulents) allow the water to be stored inside the plant and to be used during long periods of no rainfall (droughts).

Question 15

describe interdependence in a hot desert:

Answer 15

• the growth of plants is limited due to the extremes of temperature and lack of water
• therefore the nutrient cycle is very slow
• due to a lack of organic matter, the soils are coarse, sandy, and low in nutrients

Question 16

describe biodiversity issues in the desert:

Answer 16

• low levels of precipitation and high temperatures lead to low biodiversity
• therefore where water is available there are higher levels of biodiversity, and this can lead to a ‘desert bloom’, leading to over 200 species of flowers blooming, also attracting insects and lizards.
• human activities also threat biodiversity, such as mining, climate change and fuelwood gathering.

Question 17

describe how farming is an opportunity in the Mojave desert:

Answer 17

• farming: soils are poor but adding water and fertiliser can still grow crops. it’s perfect conditions for plants - sunny and hot.
  > e.g. cotton farming in Arizona, USA

Question 18

describe how tourism is an opportunity in the Mojave desert:

Answer 18

hot, sunny weather provides ideal holiday conditions. the unique and interesting wildlife and vegetation attracts many people. and barren, empty landscapes are great to explore.

• death valley national park
• las vegas
• grand canyon

Question 19

describe how mining is an opportunity in the Mojave desert:

Answer 19

• copper, uranium, lead, coal, gold
• lithium creates rechargeable batteries for cars. it’s controversial - the process spoils the landscape, but it helps combat global warming.

Question 20

describe how energy production is an opportunity in the Mojave desert:

Answer 20

wind:
- wide open spaces means wind moves more freely.
- lots of land is available.
- low population means fewer people are affected or object.

HEP (hydro-electric power):
- the Hoover Dam and Lake Mead provide hydro-electric power, and attract over 1 million tourists each year.

Question 21

describe the Ivanpah Solar Energy Farm:

Answer 21

• a solar energy farm in the Mojave desert.
• largest desert power plant in the world.
• on average 279 sunny days/year in the Mojave desert, as it’s constantly high pressure, cloudless skies.
• covers 5 square miles, powers 140,000 homes.

Question 22

why are deserts challenging places?

Answer 22

• large diurnal range. temperatures are so hot (over 40 degrees celsius) during the day but are freezing at night.
• few plants and animals can survive there.
• agriculture is hard due to the harsh climate and poor soils.
• water and rainfall are in short supply.

Question 23

how are extreme temperatures a challenge in deserts?

Answer 23

• daily temperatures can reach 45 in the day, and fall below freezing in the night.
• exposure to these temperatures can be dangerous for humans.
• during the hot season, tourists won’t want to visit, so work in the tourist industry is only seasonal.
• physical work is difficult in high temperatures, which can slow productivity.

Question 24

how is the limited water supply a challenge in hot deserts?

Answer 24

• providing enough water for workers, industry and irrigation is challenging and unsustainable.
• some areas of the Sahara only receive 70mm of rainfall every year; however, rainfall is unpredictable, and they could receive even less than that.

Question 25

how is inaccessibility a challenge in hot deserts?

Answer 25

• providing services, such as healthcare, is difficult in isolated and remote communities. (people aren’t receiving proper human rights, shortening their life expectancy and stability).
• in Mali, it takes 5 days to transport salt from the salt mines out of the desert. other minerals are taken out by air, which is expensive.

Question 26

define ‘desertification’:

Answer 26

the process of the degradation of land so that it’s more desert like. it becomes, drier, damaged and less productive.

Question 27

describe the city of Las Vegas:

Answer 27

• city in the Mojave desert - one of the fastest growing cities in the USA.
• home to 600,000 people and growing.
• relies on water from Lake Mead - 90% of its water comes from there. the other 10% is groundwater.
• attracts 37 million visitors to casinos and hotels.

Question 28

describe the water shortage in the Colorado River and Lake Mead:

Answer 28

• global warming is changing rainfall patterns, and droughts are becoming more frequent.
• this will lead to a water deficit in a fast-growing city.
• the Colorado River supplies water to 25 million people, and irrigates 3.5 million acres of farmland. so much water is being extracted from the river that it’s running at an all-time low.
• Lake Mead holds the Colorado River’s discharge, but is at record low levels, and more water is leaving than going in.
• underground aquifers also supply some of the area’s water, by it being pumped to the surface. aquifer water levels are also being depleted (going down).

Question 29

there are 6 causes of desertification. describe deforestation:

Answer 29

• trees are cut down. in LICs, this is their only source of fuel.
• there are now no plant roots to hold the soil together. this leaves the soil exposed to wind and rain, and leads to soil erosion.
• cattle starve, farmers lose their income.

Question 30

there are 6 causes of desertification. describe over-cultivation:

Answer 30

• the soil is farmed badly, using the same soil over and over again. the soil becomes exhausted of all nutrients.
• the soil becomes infertile and farming cannot continue. this can cause famine and poverty for farmers, especially in LICs.

Question 31

there are 6 causes of desertification. describe population growth:

Answer 31

• the world population is rising rapidly. population growth is especially a problem in LICs.
• with more mouths to feed, more trees are cut down for fuel, and more land is farmed. both can lead to soil erosion.

Question 32

there are 6 causes of desertification. describe climate change:

Answer 32

• global warming could alter rainfall patterns, leading to more droughts.
• more droughts would mean that crops and plants would die, creating bare soil and desert.
• this can cause famine and poverty for farmers, especially for those in LICs.

Question 33

there are 6 causes of desertification. describe over-grazing:

Answer 33

• cattle feed on grass and vegetation, removing plants and leaving bare soil which can easily be eroded.
• there are no plant roots to hold the soil together, leaving the soil exposed to the elements (e.g. wind and rain), leading to soil erosion.

Question 34

there are 6 causes of desertification. describe soil erosion:

Answer 34

• when vegetation is removed, the bare soil can easily be washed away by rain, or removed by wind.
• soil erosion can cause layers of fertile soil to be stripped away, leaving infertile land, and desert-like areas. it takes hundreds of years for new soil to form.

Question 35

how can tree plating provide a solution to desertification?

Answer 35

• the leaves protect the soils from heavy rain and high winds.
• the roots bind the soil together and stabilise it, holding it in place.
• leaf littler decomposes and releases nutrients into the soil.

Question 36

what are stone bunds, and how are they a solution to desertification?

Answer 36

• in West Africa, people have built low stone walls, that are 0.5-1.5 metres high.
• this stops water from running down slopes and washing the soil away (soil erosion).
• the walls also trap water, forming puddles, allowing it to sink into the ground. this increases crop yield by 50%.

Question 37

how can soil management be a solution to desertification?

Answer 37

• leaving areas of land to rest in between grazing or planting crops, allowing the land to recover.
• compost can be used to replace nutrients in the soil, so plants can continue to grow and hold the soil together.

Question 38

how can water management be a solution to desertification?

Answer 38

• water management is needed to stop the process of salinisation which can happen in hot deserts due to irrigation and evaporation.
• we can grow crops which do not need much water such as millet or olives.
• we can use drip irrigation instead of surface irrigation for our crop, which stops soil from being washed away by adding lots of water in one go.

Question 39

define ‘salinisation’:

Answer 39

the increase of salt concentration in soils which is caused by dissolved salts in an excessive water supply.

Question 40

describe the Great Green Wall project:

Answer 40

a tree planting project which is being put in place along the Sahel region.
- act as windbreaks to protect the soil from soil erosion.
- tree roots can stabilise the sand to prevent the desert from encroaching on farm land.

Question 41

what is the issue with the Great Green Wall project?

Answer 41

it’s a good idea, but they’ve been doing it for 10 years and its still not complete. it’s too expensive, and there’s a lack of motivation to carry it out in the poorer countries that it passes through.

Question 42

describe fuel-efficient stoves:

Answer 42

• use less wood as the heat is held inside and not lost. this means that less trees are cut down around villages, slowing down desertification. also saves people time from cutting and collecting wood.
• they cook faster; are cheap and easy to buy and construct.
• give off much less smoke, better for people’s health.