i think the climatologists definition is the more accurate because temperature and rainfall are responsible to generate all the other aspects, for instance saltlakes, sabkhas and many other desert sub-enevironments are developed only under certain climatic conditions.

The following article comes from the southwestern region of the USA, and discusses at length exactly the issue you're dealing with, and offers different concepts to apply to find more useful information about the system. 

http://www.esajournals.org/doi/abs/10.1890/140276

Definitions are context-dependent. Deserts are not necessarily resource-poor; depends on what definition of a 'resource' is. Biodiversity is a resource--the raw material of ecosystem adaptability to changing conditions, and deserts are biodiversity-rich. 

Are you interested in a definition of a 'desert' so you can talk about desertification?

I think that definition of desert belong to temprature and precipitation but you know that there are glacial desert and tropical deserts, any way in desert  basic factors  of life do not exist, so man and animals and plants can be hardly, dreeting

Dear Dr. Kosroshahi:

Here is the definition of this technical term used in morpho-climatic studies and during investigaton of vegetation geography:

- A region with a mean annual precipitation of 250 mm or less,

- devoid of vegetation as to be incapable of supporting any

considerable population.

Four kinds of deserts may be distinguished:

polar or high-latitude deserts, marked by perpetual snow cover and

intense cold;

(2) middle-latitude deserts, in the basinlike interiors of the continents,

(e.g, Gobi) characterized by scant rainfall and high summer

temperatures;

(3) trade-wind deserts, notably the Sahara, with negligible

precipitation and a large daily temperature range

(4) coastal deserts, as in Peru and Chile, where there is a cold current on the western coast of a large land mass.

Best regards

Harald G. Dill

There are various technical definitions of desert depending a bit on which branch of science somebody follows. However one single characteristic common to ALL type of deserts is their vast "empty" space because of absence of any visible biological life. So any area with these attributes is a desert : from latin "desertus": abandoned by life 

Dear Julius Jara-Muñoz:

There are areas with rainfall higher than 400-500 mm, but because of land inappropriate formations(like gypsum and salt), the plants can not grow there. so, although these areas are not desert in point of climatology but the geological aspects, are desert.

ِdear prof, Harald G. Dill

In order to recognize and mapping domains of the real deserts, it is needed to gather a tremendous data and information regarding environmental parameters such as Geology, Geomorphology, Climatology, Hydrology, Pedology and Vegetation cover. In fact these environmental parameters and their interaction effects lead to form and develop the real deserts.

Types of the desert you introduce, are only climatic deserts. Because all these definitions is mentioned only rainfall and temperature. Certainly you know in some deserts, There are areas with rainfall higher than 400-500 mm, but because of land inappropriate formations(like gypsum and salt and so on), the plants cannot grow there.  So, In this deserts the role of Geology is important no Climatology.

Dear Mr. Michael Reynolds Chang

When I saw your photo, I thought it is belongs to George Bush, the former President of America. It is very look like him .OK, i will be grateful to you for introduce website for article. In this question we discuss about desert and no Desertification. Because definition of Desertification is clear and accepted by the international community, but we do not have a comprehensive definition for desert that accepted in the world

ِDear prof, Abdul Atheem Mushtaha

I think if we should accept a general definition for the desert, The last part of your offer is more suitable. Although in many desert areas, the life is exist for example in many African countries.

Dear Dr.  Kosroshahi,

duricrust like gypcretes, dolcretes or any other encrustation near surface result from evaporation and have to be considered as part of desertification . Geology can never be a criterion for a desert. Geology only responds in a different way to morpho-climatic changes at the interface between atmosphere, pedosphere, hydrosphere and lithosphere. If we expand the technical term "desert" in an way like that we have to follow up peodology where even soil formation on a waste dump is given a name of its own, called "technosol". Deserts have evolved through the geological past until the Recent following the above classification scheme and the constraints reported.

Let me know the region where you have an average rainfall of 400 to 500 mm (on an annual basis) and a desert comes into existence and persists.

Best regards

Harald G. Dill

A desert is a region devoid of vegetation or sparsely covered by xerophilic plants (e.g., Artemisia spp., cacti). The common geographic definition of a desert is a region with less than 100-125 mm (desert) or 100-125 to 250mm annual precipitation (subdesert or semi-desert). Of course, temperatures play a role: high temperatures enhance evaporation and by consequence, aridity.

Tropical deserts are to be found on western sides of continental masses (Sahara-Arabia, Western Australia, Kalahari, Atacama desert in Peru and Chile) because of the atmospheric circulation (high atmospheric pressures). The Atacama desert is the driest place on Earth (mean annual precipitation is only 1 mm).

Other deserts are located in interior plateaus "protected" by mountains. In fact, the relative humidity of the air increases when it descends from the surrounding mountains, which impedes condensation and precipitation (e.g. the interior plateaus of the Western U.S., Patagonia; in both cases the prevailing winds are westerlies).

The tundra of the Arctic North is a special case: precipitation is low, but evaporation is too. The major factor preventing trees and shrubs from growing is not the lack of precipitation but the shortness of the warm season.

Salt and sand dunes seem to be a factor, but without evaporation, salt wouldn't have accumulated at the surface (e.g. in the Saharan sebkhas) and sand dunes wouldn't have been formed by eolian processes without the absence of vegetation. In a more humid environment, vegetation would have grown, humus would have formed, and eolian processes stopped.

So the absence of soil, as in the sandy Saharan ergs or the rocky Saharan regs, is a not a factor of the lack of vegetation, but a result of the lack of precipitation.

Sorry for the lapse: I should have said: the relative humidity of the air DECREASES when it descends from the surrounding mountains

Professor Kosroshahi:

It IS former president George W. Bush. The picture makes me laugh, so I keep it. The world is dark and heavy. Laughing at Bush makes me feel light.

I believe that in the article I attached discusses precisely what you're getting at: many complex factors intersect to create desert. Climactic determinism is an insufficient criterion for defining desert. Desert as a state of being and Desertification as a state of becoming are like position 'x' and velocity 'dx/dt' in newtonian motion. I question the 'internationally accepted' definition of desertification because there is no accepted definition of desert. How can you know dx/dt lacking knowledge of x?

Do you see the dilemma? Definitions lack intrinsic value. They are valuable based on the question you want to ask. What is your question? The article examines different ways to address whatever question you may have, and may allow you to circumnavigate the difficult question of defining a desert. 

Best,

Michael Chang

Dear prof.Harald G. Dill.,  thank you so much for your attention.

In my country, There are thick layers of gypsum and salt and evaporate rocks in the mountains of central and coastal areas. also there are many salt domes in some of southern and central plains. these formations are belong to thousands centuries ago that have been an effective role in the formation of desert areas. Such geological formations which have restrictions for vegetation growth were named “Primary deserts” .

The biggest problem is the presence of evaporate deposits geological formations such as gypsum and salt content, which are in most parts of Iran. These structures act as a center for spreading salt by surface water and possibly wind and the deep penetration. These areas that formed from thousands years ago, are named "secondary deserts". Of course may be you say this part is desertification. it is true but it happened many centuries ago and there is not any vegetation and life there.

Related to second question, in Iran there are some areas in Zanjan and Azarbeyejan province and other, that have high precipitation(more than 400 mm), but they are desert because there are Marl formation and vegetation can not grow there.These formations are often seen as Badland .

with best regards

Desert is a climatic notion with consequences on pedology, geomorphology, life, etc. It can not be reduced to an amount of rain but, in my opinion, it is defined by an hydric budget : cold climate as Antarctica for instance, receive may be less than 50 mm/year but are not deserts because there is not a lack of water. The desert begin where the water deficit is too important, that includes temperature, capacity of evaporation, etc. So, I think the best way is to compare ETP (Potential Evapotranspiration) and ETR (Real Evapotranspiration) which depends both on ETP (capacity) and available water.

Desert; simply is an area where the annual rain fall is less than 150 mm, not necessarily to be covered by sand !!, both Iraqi Western and Southern Deserts are covered by limestone and residual soil, no even a single sand grain, as sand dunes.

Dear Patrick Mangou

if you see my question reply in this option, you will understand why we can not have an integrated definition for desert. because everyone introduce desert on the basis of it's specialty. Even those introduce desert only on the basis of climatic parameters say different amounts of the rain. I've seen a lot of resources which have introduce desert, with rainfall of 50, 100, 125, 150, 200, 250 and even higher.

best regards

Dear Pierre Carrega

As may be inferred from the difficulties in defining and delimiting deserts, they do not present a homogeneous landscape. Long-term differences in climatic, tectonic, biological, and geologic history cause deserts to be individually distinct. Each tends to have a unique assemblage of landscape elements and processes. Geomorphologically, the North American deserts are dominated by the erosional and depositional effects of surface water; the eastern Sahara by aeolian processes; and the Atacama by extreme aridity, barren landscapes, saline deposits, and mass wasting that is enhanced by earthquake activity (Oberlander 1994). Deserts also vary tremendously in their tectonic settings. The stability and age of Australian deserts contrasts sharply with the youth and tectonic instability of arid North America. Furthermore, unique landscape assemblages bear the imprint of climatic change over long time periods.

regards

Dear Dr. Khosroshahi

The term desertification seems to mean different things to different people. Broadly defined as reduction of the biological potential of land in arid and semi-arid areas, there are three main effects: change in aridity, vegetation species change, and change in soil properties.

Can one tell if a desert exists from a photograph?  If so, what indicates a desert exists?  If not, what indicates a desert does not exist?

Dear Dr. Khosroshahi

in the introduction section of this paper we made a review of the topic. Hope it is useful for you.

Conference Paper Numerical model to evaluate the mitigation strategies to com...

Sorry this is the full version of the paper.

Article Numerical model to assess the impact of the strategies to mi...

Dear Carla Ximena Salinas

Thank you very much for your cooperation and your article. in this article you have discussed about desertification. i ask for about desert no desertification. in your mind, what or where is desert. there is no comprehensive definition for desert that is accepted by most of the experts and Different Sciences Scientists.

thanks again

Dr. khosroshahi 

Hi Mr. Mohammad Khosroshahi,

According to Wikipedia the desert is defined as " A desert is a barren area of land where little precipitation occurs and consequently living conditions are hostile for plant and animal life". The little precipitation is the matter of debit, I mean how much is the "Little". But, as far as I know not more 150 mm per year, this amount is considered in Iraq for long time ago, and I guess majority of Iranian desert has almost the same characters of the Iraqi Southern and Western Deserts.

Varoujan Sissakian

Private Consultant Geologist

Iraq

Hi James, thank you for your comment, I would like to add that no sand dunes occur in the Iraqi Deserts. the clayey soil is very fertile and in rainy years, amazing amount of green cover with beautiful colored flowers can be seen every where in the Iraqi Desert. Moreover, seasonally the valleys are flooded with enormous damaging ability. Some of the large valleys has length of few hundred kilometers, yes few hundred, with width ranging from 100 m to about 1 Km, the depth ranges from few meters up to 120 m, so you can imagine the erosion ability.

Dear colleague , 

Good question but difficult response. In reality, there are common elements ; Low plant biomass and vegetation cover, Scarce rainfall and landscape type "desertic" made of glazes and Hamada, paved by regs and sandy accumulations. But precipitation thresholds , plant cover proportions change slightly from landscapes of desert to another. In addition, as you know there is hot and cold deserts.

This is an interesting question. There are cold deserts (in Cananada, parts of the Oltenia Plain in Romania, and many other) and hot deserts. I would recommend Piers Blaikie's book on the Soil Erosion - it is a debatable subject. I have written an essay on this 20 years ago and started with Piers Blaikie's book the political ecology of soil erosion. If I can find it I will up-load it. My Professor at the time encouraged me to publish it as an article. I will one day.  Royal Holloway College (Univ of London), the Geology and Geography Dept have avery good course on soil erosion and desertification. Check their web-site. Prof. David Simon as well.

Dear Mr. Sissakian‎, Ewart Bowkett, Azziz Hirche and Cristina Posner ·

Thank you for your interest and your participation in this discussion.Your talking about the desert, are right. But as you see, each of you has a different view in this issue. Some of you have pointed more to the climate and some geomorphology and some erosion and so on. This is one reason that we cannot have a comprehensive definition for desert. So, In order to recognize and mapping domains of the real deserts, it is needed to gather a fermendous data and information regarding environmental parameters such as Geology, Geomorphology, Climatology, Hydrology, Pedology and Vegetation cover. In fact these environmental parameters and their interaction effects lead to form and develop the real deserts. Thus in this subject we must try to study the most specification of desert to seek these processes based on related sciences.

and thank you Dear Mr. Mohammad for your excellent contribution

Regards

Varoujan

I am going to include an answer about Natural and Man-made deserts.

LOW RAINFALL is the beginning of my answer, so that could be 50 cm. of annul rainfall or less.  The next question, is this a man-made or natural desert?  And one answer could be--Were domesticated animals there at any time over the last 6,000 years? If so, it is probably a man-made desert.

MAN-MADE deserts were created hundreds or thousands of years ago, when we put domesticated animals there and killed their preditors. North America 100-200 years ago, Middle East 2,000-2,500 years ago, Indus Valley and Western India 3,500 years ago, or North Africa 5,500 years ago. 

The Indus Valley man-made desert was created when the trees were chopped down for firewood or to bake bricks, and the perennial grasslands were are grazed to dust. Once they turned their forests into firewood for their bricks, five million people had to abandon their 1,000 cities forever.

Once a man-made desert is established, we still maintain these former natural arid grasslands as “deserts” with our domesticated animals, not allowing the local perennial grasses to recover.

In California this year, the Federal BLM is letting 300 head of private cattle, to try and find enough feed on 200 square miles (52,000 hectares), and this pattern is copied each year on what looks like natural “deserts” but is actually continually being maintained as “man-made” deserts by our domesticated animals. (See Ord Mountain allotment on the web).

SOIL NUTRIENTS--Then, when we look deep into the top 10 cm of the soil surface, we see what the domesticated animals walked away--Not only with the perennial native grasses and wildflowers in their bellies, but also with the soil organic matter and the soil nutrients that the grass seedlings needed to survive.

Each species of native grass has a soil organic matter and soil nutrient threshold level they need to survive as seedlings.  Without it, the perennial native grasses cannot recover, as you can see from the paired photos at http://www.ecoseeds.com/good.example.html.

That webpage shows taking soil from around existing mature native grass plants and put it into two boxes, the box on the left no organic matter or fertilizer, and on the right, the organic matter and fertilizer the seedlings needed for survival.  On the left, the seeds sprouted and died, on the right thrived. 

This conversion from a solid perennial grassland, to what looks like a desert, can occur in less than 100 years, as you can see in Dr. Humphrey’s paired photos at http://www.ecoseeds.com/desertgrass.html.

Another test you can do is an age-pyramid on a stand of perennial grasses. Measure the basal diameters of 100 plants of the same species, and see how the diameters sort out--do you have mostly old plants, or do you see a lot of young seedlings?

Removal of the soil nutrients is one issue, but did you also remove the Pseudomonas host plants as well, then, that is double-trouble for your man-made desert, because you have now permanently lowered the annual rainfall for the area as well. 

You can see the contrast from the mountains above Salalah Oman where the Pseudomonas host plants still live, and the rest of Arabia that is man-made desert, like the paired photos at http://www.ecoseeds.com/cool.html or http://www.ecoseeds.com/salalah.html.

I have many questions posted about the “Pseudomonas” and “clouds” when you put those two words and search in the “questions” box on Research Gate.

And if you check my Megatransect page at http://www.ecoseeds.com/mega.html for Oman and Saudi Arabia, you will see where I have rated the potential of each site for ecological restoration of the native grasslands.

So the bottom line on “deserts” --are they NATURAL (in that domesticated animals were never there) or MAN-MADE--at one time or another the perennial native grasslands and/or savannahs were converted by domesticated animals to what today looks like a “desert”. 

=======

Hello M.K.: A recent book, THE ARID LANDS: HISTORY, POWER, KNOWLEDGE (2016, MIT Press) by Diana K. Davis really altered my thinking on deserts, most of which was out-dated since my university days half a century ago. Currently, I simply view deserts as: places where man equipped with only simple technology still struggles to survive but where man equipped with modern civilization's technology can flourish. The key is mankind's harnessed energy and its manipulation in powerful machines. Obviously, deserts can be cold (Antarctica), hot (Sahara) with varying kinds of terrain and terrane. So, it really only matters, if we speak from a purely human perspective, whether such places are amenable to our transformation into something we desire as a species.

Richard.

Agreed with Dr. Mohammad. For a comprehensive definition of desert from identification and further mapping of features, there is a need of datasets reg. various parameters/ themes viz. Geomorphology, Physical Geology, Geology, Hydrology, Climatology, Pedology, Vegetation etc., as desert itself refers to an ecosystem formed by variables or themes stated above and like ones.

Dear Dr. Atul Kohli

thank you for your attention about desert and it's comprehensive definition.

Atul Kohli fails to recognize a very pertinent fact: "desert" is a human-contrived description of an apparently singular Earthly landscape. All the verbal means we employ to specify its natural characteristics are also human contrivances--literally, figments of our imaginations. His answer, therefore, is circular and not particularly useful.

Dear Prof.Richard B. Cathcart

Thank you very much for your participation in the desert discussion. our discussion here is about deserts caused by natural factors, not human deserts. Humans can make a difference in any environment, just as desertification is influenced by humans and natural factors. Also, in my question, I have written detail different definitions of the desert, especially deserts caused by natural factors.

You wrote that all deserts are man-made. Can we say the subtropical deserts on the Earth are also man-made? Certainly not ( Please see the attached image). I would be grateful to you if write a definition of the desert. I'm sure you can not give a complete definition of the desert without environmental factors.

This is Cart before the Horse thinking: I was speaking of human definitions of deserts because we are the ones apply that word to a certain region, which is of course natural. Although, there are regions which have become desert-like because of anthropogenic actions. Besides, what is "desert" to urbanized peoples may not be considered so by those born, bred and reared in dryland places.

I agree with Dr Cathcart that all of those descriptions are human creations. They look at only specific elements of the environment but do not generally describe the common elements of all deserts, which is arid conditions. Deserts, cold or hot, have a basic lack of water. Hot deserts tend to be low lying and cold deserts may be low or high (mountaintops), but all tend to be on the western side of continents, and all have limited available water resources. Soil types, flora, and fauna all vary widely, so none of those descriptions are applicable to deserts in general, only to specific deserts.

Dear Monty Watson: Thanks for apprehending my meaning. People, perhaps solely plied by sensationalistic even child-like media reports of Science's factual findings, are all too willing to sign-on to "the Anthropocene". Yet, they do not seem to realize that by doing so, they make it clear that people--no matter how hazy their thinking or their inexperience of geophysical event-processes--really do define their surroundings (the actual world) with self-serving assumed ease. ODD, unrealistic mumbo-jumbo. In recent years, I have noticed that more and more scientific reports and, thus, the summarizations in popular media, seem utterly reliant on dictionary-style definitions as a BASIS. Of course, we do need common terms of reference such as those you are seeking, but what is all-too-common today are regurgitations, not sound thinking. Egoists who fill their reports with "I", "We" etc. are really pursuing publicity, publicity to generate more funding to continue their work in sloppy Science creation. SAD. The ultimate in Anthropogenic reaction would be to move the Solar System, but to leave Earth behind when we do so since it is verging on complete breakdown, all caused by Homo sapiens sapiens. I wonder, has anyone yet considered the possibility of a Cosmic Junkyard?

Dear Mr. Monty Watson

Thank you very much for your participation in this subject. you mentioned about cold and hot Deserts for its lack of water. OK, it is right. Why do you call these areas desert? Is not it because there is no plant there? In cold and polar deserts, there is a lot of snow and rain (unlike hot deserts), but it is in the form of ice and The root of the plant cannot use it. there are also other deserts near the seas, but for some reason (such as high salinity of soil and water) the roots of the plant cannot use it. it is, lack of water is known as a limiting factor in biological processes. this means, both areas are affected by drought but of the physiological drought type. so, in these areas, two main factors play a role in determining deserts. Two natural factors such as climate and vegetation (no human). although the excessive human intervention has also led to the emergence of man-made deserts. anyway, the investigation of the available sources on the concepts and characteristics of the desert shows that, there is not a comprehensive and unified definition for desert areas. In expressing the characteristics and concept of desert ecosystems, different sources have provided different definitions. In this case, each of the scientists of different sciences have introduced only the characteristics of desert areas from their expert point of view. for this reason, I have asked scientists and experts in related fields for a comprehensive definition of the desert that includes all the factors that contribute to desert formation. at the end, I would like you to tell me what is a desert? and also tell me what criteria we should use to identify and determine for desert areas?

with best regards

Since "deserts" seem to be hot or cold and the criterion is the liquidity or not of water, then might it not be that "deserts" are generally speaking just human-delimited, perhaps sometimes even demarcated, planetary landscapes wherein liquid water is unavailable to some/any/all life-forms?

What is an “integrated definition?”

In many cases, definitions are just “operational definitions."

What is light?

You may be interested in:

https://www.researchgate.net/publication/314933544_DESERT_ECOLOGY; and

https://www.researchgate.net/publication/302587271_Desertification .

Good Luck,

Jack

Dear Jack Kornfield

Thank you very much for the documents you sent. As mentioned in that article, some criteria such as climate, soil, plants, geomorphology, Geology and even animals are used to determine desert areas. but I say the definition of a desert is not easy, especially in quantitative terms, because there are differing disagreement and difference in opinion of scientist. Let me give you an example. Suppose you or I want to define and map the desert border in our country. I am just referring only the climate criterion here (no other criteria) and you see there are very different ideas for defining the boundaries of deserts. for example:

Fink has identified areas with an annual rainfall of less than 500 mm as arid and said if it is less than 250 mm, it is a desert area.

Ganssen considers lands with less than 350 mm of annual rainfall to be dry, and if this amount reaches less than 125 mm, the area will be completely arid and desert.

Silianov in Russia, has proposed a relation for the introduction of the desert based on the ratio of humidity and temperature. he introduced a coefficient of 0.5 for used to separate the border of desert areas.

FAO has also identified desert areas with an annual rainfall of less than 200 mm.

Monique Menge (1995) in her book (man and drought) called very dry (10 to 50 mm) rainfall, desert (50 to 100 mm), semi-arid (150 to 500 mm) and semi-humid arid (500 to 800 mm).

Dresch, Jean (1982) used a coefficient of rainfall variation to introduce the desert and determined its from 25 to 40%. While Singh introduces this amount from 30% to 70%. and so on.

Therefore and as I have told, there is no common opinion on the desert by experts and scientists. However, there are similar differences in other criteria such as soil, plant, geology and geomorphology. That is why it is not easy to define and separate the desert in an area.

M.K.: all you say is true. So, why not simply define deserts as you see fit in a way that serves your purposes, whatever they may be?

Dear prof. Richard B. Cathcrat

Thank you very much for your participation in this discussion.

I wanted to have the opinion of scientists and experts in this field and reach a complete conclusion of the desert.

with best regards

Dear Dr. Khosroshahi thank you for this nice topic about desert.

The main environmental factor controlling any chemical reaction can be water from living being to non-livings. Therefore, water in form of humidity or vapour (atmospheric and soil) could be a critical element that could allow Scientists to identify which area can be considered as forest, savannah, steppe or desert. It could be hard to speculate that both deserts hot and cold do not have living organisms; in any of these types of deserts, there are different types of organisms from microscopic to macroscopic. However, their respective physiology was adapted to each one these. Finally, desert could be defined as geographical zones where any environmental reaction is strongly controlled by water limitation (humidity and vapour).

Dear Mohammad , please take a look at this new paper. The concept of deserts was re-visited last year: Article Desertifying deserts

Dear Tsombou François Mitterand

Thank you very much for your participation in this discussion. In my opinion, it is a bit difficult to have a comprehensive and complete definition agreed upon by scientists in this field

Dear Arthur Prudêncio de Araujo Pereira

Thank you very much for the good introduced resources.