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Is there available information on how much of Earth surface is arid climate?

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  • $\begingroup$ I'm glad you liked the answer. However, I wonder How the question you mention would be answering your question? $\endgroup$ – Camilo Rada Mar 22 '18 at 17:33
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    $\begingroup$ May be I wronly assumed that by "dry land" he meant "arid" ? Did he just mean "land"? $\endgroup$ – Pablo Mar 22 '18 at 17:38
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    $\begingroup$ I see. Yes, I think that question refers just to land, or in other words: Earth's surface not covered by water. $\endgroup$ – Camilo Rada Mar 22 '18 at 17:46
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    $\begingroup$ It would be desirable if you edit your question accordingly, to do not mislead others that might end up here looking for the same answer. $\endgroup$ – Camilo Rada Mar 22 '18 at 17:49
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It will depend on the exact definition of "arid" and the period of time. But using the widely used and accepted Köppen climate classification, "arid" would correspond to the four climates in climatic group B: "Dry (desert and semi-arid) climates". Using the most up-to-date present climate data (2006) provided by the WORLD MAPS OF KÖPPEN-GEIGER CLIMATE CLASSIFICATION at 0.5° of resolution, that looks like this (in an equal area projection):

enter image description here

We get that the four arid climates (group B), add up to $4.401 \times 10^7 {km}^2$ of a total of $1.527 \times 10^8 {km}^2$ inventoried in the dataset (A good match for the figure of of global land area of $1.489 \times 10^8 km^2$ listed by wikipedia), leading to a grand total of 28.8% of Earth's land surface corresponding to arid climates.

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    $\begingroup$ I'd think perhaps that number is a bit high, owing to the coarse resolution. E.g. the northeastern part of Africa has the non-arid Nile valley & delta, which is too small to show up on the map. $\endgroup$ – jamesqf Mar 22 '18 at 19:12
  • $\begingroup$ @jamesqf I guess ~50 km resolution is more than enough to identify climates, anything smaller would be most likely a microclimate. And in any case. Why coarser resolution would bias to higher values for arid areas? Arguable, also small arid areas would be missing. $\endgroup$ – Camilo Rada Mar 22 '18 at 19:28
  • $\begingroup$ I think it depends on exactly what the OP is asking for. There are areas (I live in one) which are arid if considered from a climate perspective - that is, very little rainfall - but which have non-arid climate vegetation due to water from streams and/or aquifers. Those zones are often long & narrow, like the Nile valley or the areas on the leeward sides of mountain ranges, so averaging over a coarse grid misses them. $\endgroup$ – jamesqf Mar 23 '18 at 17:54
  • $\begingroup$ @jamesqf Well, that's what I meant by "It will depend on the exact definition of arid", I took common definition of arid as given by the Köppen classification, which doesn't consider vegetation type. Of course, with a different classification the answer would be different. But, as the OP didn't pointed any specifics I guessed he did not care on those subtleties. And instead of specifying a definition of arid he went on to accept the answer, so I guess it was OK. But you are right in the sense that the answer depends on the climate classification used (as I stated at the start of the answer). $\endgroup$ – Camilo Rada Mar 23 '18 at 19:14
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ARID LANDS: CHALLENGES AND HOPES by EARTH SYSTEM: HISTORY AND NATURAL VARIABILITY – Vol. III - Arid Lands: Challenges and Hopes - Barakat H.N.

Hyperarid zones cover 7.5% of Earth's land surface, arid zones cover 12.1%, while semiarid zones are more extensive, occur in all continents, and cover 17.7% of Earth's land surface. The dry subhumid category covers 9.9% of Earth's land surface.

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