Online Geography Resources


Agriculture in Hot, Arid Environments

IB DP Geography
Next page
Base Knowledge and Understanding

Base knowledge and understanding


[Watch from 2:28 to 12:49]

Drâa Valley Precipitation, Morocco
Video Clip
Data Visualization
Definition aridity
flood irrigation
sprinkler irrigation
drip irrigation
News Article
Words to be defined
Base Level



Lesson Aim

  • To be able to examine the opportunities for agriculture in hot, arid environments
  • To be able to examine the distinction between aridity and infertility.
  • To examine the importance of irrigation.
  • To examine the risk of salinization.
  Syllabus linkage: Freshwater - Irrigation and agriculture

Option 1

Take notes by hand
Answer the questions by hand - no note-taking frame

Option 2

Google Documents note-taking frame
Answer the questions using this Google Documents note-taking frame
Geography Activities
Geography Activities

Aridity and/or Soil Fertility

Aridity is usually expressed as a function of rainfall and temperature. A useful "representation" of aridity is the following climatic aridity index:


where: P = precipitation ETP = potential evapotranspiration taking into account atmospheric humidity, solar radiation, and wind.

Three arid zones can be delineated by this index: namely, hyper-arid, arid and semi-arid. Of the total land area of the world, the hyper-arid zone covers 4.2 percent, the arid zone 14.6 percent, and the semiarid zone 12.2 percent. Therefore, almost one-third of the total area of the world is arid land.

The hyper-arid zone comprises dryland areas without vegetation, with the exception of a few scattered shrubs. True nomadic pastoralism is frequently practiced. Annual rainfall is low, rarely exceeding 100 millimetres. The rains are infrequent and irregular, sometimes with no rain during long periods of several years.

The arid zone is characterized by pastoralism and no farming except with irrigation. For the most part, the native vegetation is sparse, being comprised of annual and perennial grasses and other herbaceous vegetation, and shrubs and small trees. There is high rainfall variability, with annual amounts ranging between 100 and 300 millimetres.

The semi-arid zone can support rain-fed agriculture with more or less sustained levels of production. Sedentary livestock production also occurs. Native vegetation is represented by a variety of species, such as grasses and grass-like plants, fortes and half-shrubs, and shrubs and trees. Annual precipitation varies from 300-600 to 700-800 millimetres, with summer rains, and from 200-250 to 450-500 millimetres with winter rains.

Soil fertility is the ability of a soil to provide nutrients for plant growth. Not all soils in arid environments lack the necessary nutrients to be productive but the lack of available water limits plant growth and agricultural potential.

Geography Activities
Geography Activities



Flood Irrigation

Agriculture in Extreme Environments - Flood Irrigation
Results in a large surface area of water since furrows between crops will be filled with water. It is simple, relatively cheap, requires little energy and can use lower quality water than other systems. Conventional furrow systems are only 60% efficient in water absorption by the plants.

Sprinkler Irrigation

Sprinkler systems use spray nozzles and pressurized water and can either be movable (such as center-pivot) or fixed. The most efficient systems are Low Energy Precision Application (95%) and Low Elevation Spray Application (88%) sprinklers. They are an adaptation of center-pivot irrigation in which the nozzles extend right down to the ground so the water is supplied only and exactly where it is needed and can be applied at low pressure. This saves water as less is lost to wind or evaporation from the foliage and energy as well as preventing soil erosion caused by runoff of excess water. On the down side sprinkler systems are expensive to install and may become less efficient when it is dry or windy, and they may damage crops by frequently wetting non-root areas.

Drip Irrigation

Drip irrigation
This is where water is supplied at very low pressure, very slowly, directly to a plant's roots from plastic tubing. It is the most efficient form of irrigation at 97%, results in very little erosion. However it is also the most expensive form of irrigation. Adapted from Source
Geography Activities
Geography Activities

Risk of salinization

Evidence of salinization in flood irrigation channels, Morocco

Soil salinization is one of the major threats in irrigation agriculture. Soil salinity causes yield losses and can lead to structural instability of the soil if the sodium percentage is high. Salinization is reducing the world's irrigated area by 1-2 percent every year, hitting hardest in the arid and semi-arid regions.

Primary salinization occurs naturally where the soil parent material is rich in soluble salts, or in the presence of a shallow saline groundwater table. In arid and semi-arid regions, where rainfall is insufficient to leach soluble salts from the soil, or where drainage is restricted, soils with high concentrations of salts may be formed.

Secondary salinization occurs when significant amounts of water are provided by irrigation, with no adequate provision of drainage for the leaching and removal of salts, resulting in the soils becoming salty and unproductive. Salt-affected soils reduce both the ability of crops to take up water and the availability of micronutrients. They also concentrate ions toxic to plants and may degrade the soil structure.

The salt balance of soils can be significantly affected through improper soil and water management, for example through: improper irrigation schemes management, including: 

  • insufficient water application; 
  • insufficient drainage; 
  • irrigation at low efficiency (where most of the water leaks into the groundwater) and/or over-irrigation contribute to a high water table, increasing drainage requirements and causing waterlogging and salinity build-up; 
  • irrigation with saline or marginal quality water, which may be caused by intrusion of saline water into fresh water aquifers in coastal zones due to overpumping.
Geography Activities


Geography Activities
Geography Activities

Opportunities for agriculture in hot, arid environments - The Drâa Valley, Morocco

The Draa Valley from Agdz, Morocco
Cash crops and irrigation - growing Pastèque [Water Melons] in the desert, nr Zagora, Morocco
Desert agriculture - outside Zagora, Morocco
Roadside desert agriculture, Zagora, Morocco
Conceptual model of the effects of temperature and precipitation on the difficulty of developing sustainable agro-ecosystems in semi-arid regions
IMPETUS Atlas Morocco
Invest in Morocco
Geography Review



Exam style question:

“Agriculture in hot, arid areas is difficult.” Discuss this statement. [10 marks]

The markbands can be found here - you need to look at Paper 2.

Essay Graphic Organiser on facebook
Follow @gatwUpdates on twitter
© 2006-2021 - All Rights Reserved - Author: Richard Allaway | Logout