Preprints
https://doi.org/10.5194/egusphere-2026-3062
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/egusphere-2026-3062
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
02 Sep 2026
| 02 Sep 2026
Status: this preprint is open for discussion and under review for Geoscience Communication (GC).
GC Insights: On The Definition of Aridity in Geoscience Research
Abstract. Aridity is a fundamental concept used across geoscience to describe water-limited environments, yet the scientific community currently uses multiple contradictory approaches to communicate aridity science. Here, we present the scope of aridity definition divergence, showing that out of 1000+ assessed studies aridity, A, is commonly defined as both the ratio of precipitation, P, to evaporative potential, EP, as A = P/EP (32 % of papers) and as its mathematical reciprocal A = EP/P (23 % of papers), or is not defined at all (29 % of papers). Based on this split between opposing definitions, we suggest standardization of the meaning of aridity for more effective interdisciplinary communication, accurate modeling, and metanalyses pertaining to water scarce regions.
How to cite. Good, S., Haagsma, M., Avila, C., Bulter, Z., Barinas, G., Chen, H., and Huang, T.: GC Insights: On The Definition of Aridity in Geoscience Research, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2026-3062, 2026.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
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Latest update: 14 Oct 2026
Stephen Good
CORRESPONDING AUTHOR
Department of Biological and Ecological Engineering, Oregon State University, Corvallis OR, USA
Water Resources Graduate Program, Oregon State University, Corvallis OR, USA
Marja Haagsma
Department of Biological and Ecological Engineering, Oregon State University, Corvallis OR, USA
Colton Avila
Department of Biological and Ecological Engineering, Oregon State University, Corvallis OR, USA
Zachariah Bulter
Department of Biological and Ecological Engineering, Oregon State University, Corvallis OR, USA
Water Resources Graduate Program, Oregon State University, Corvallis OR, USA
Civil and Construction Engineering, Oregon State University, Corvallis OR, USA
Garbriel Barinas
Department of Biological and Ecological Engineering, Oregon State University, Corvallis OR, USA
Water Resources Graduate Program, Oregon State University, Corvallis OR, USA
Han Chen
Department of Biological and Ecological Engineering, Oregon State University, Corvallis OR, USA
Tingting Huang
Department of Biological and Ecological Engineering, Oregon State University, Corvallis OR, USA
Water Resources Graduate Program, Oregon State University, Corvallis OR, USA
Short summary
Geoscience research exploring how study subjects are influenced by how much water is available on the earth’s surface often uses the word ‘aridity’. This work reviews the history of aridity and how geoscientist define it, including the two most common and opposite definitions. We advise researchers to use the more intuitive meaning of aridity, where a high aridity is used to describe a dry place, in order to clearly communicate research findings.
Geoscience research exploring how study subjects are influenced by how much water is available...
In the manuscript “On The Definition of Aridity in Geoscience Research”, the authors assess how aridity is defined across more than 1,000 studies indexed in Web of Science. They show that aridity is commonly defined as both Ep/P and its inverse P/Ep, while a substantial fraction of studies does not provide an explicit quantitative definition. They further highlight how the use of these definitions developed through time and among research areas and argue that EpP should become the common definition.
It is my assessment that the topic is relevant and well suited for Geoscience Communication. The manuscript is concise and generally well written and addresses a genuine problem in interdisciplinary geoscience. I agree with the authors that clearer and more consistent communication would be beneficial. However, I believe that the interpretation of the observed differences between disciplines and the resulting recommendation require further discussion. In addition, some aspects of the literature assessment need clarification. However, I think this a worthwhile and timely short communication, and I recommend publication after addressing my comments below.
Major comments
My first main point is that the disciplinary differences shown in Figure 1 deserve more discussion. The manuscript currently frames the coexistence of Ep/P and P/Ep mainly as an inconsistency (partly due to historical reasons) that should be resolved by agreeing on a single definition. However, both formulations may have advantages and disadvantages depending on the scientific perspective. I find it particularly interesting that Ep/P is more common in water-resources studies, whereas atmospheric-science studies tend to use P/Ep. I think this, at least partly, reflects also contrasting perspectives. Water-resources research often focuses on atmospheric evaporative demand relative to atmospheric water supply to the land surface, for which Ep/P is more intuitive. Atmospheric research may more commonly consider precipitation relative to the ability of the atmosphere to draw water from the surface. I therefore suggest discussing whether the disciplinary differences identified in Fig 1 partly also reflect different perspectives rather than only inconsistencies. I agree that Ep/P has the intuitive advantage that aridity increases with increasing values (I am hydrologist, so I may be biased as well). However, this does not necessarily make the inverse formulation less relevant, especially in disciplines where P/Ep may have an established physical interpretation. I suggest the authors still recommend Ep/P as a common definition, but this recommendation should acknowledge the reasons why other communities may use P/Ep. I guess a practical recommendation to always state the underlying equation and indicate the direction of increasing aridity may be at least as important as defining a common ratio.
My second point concerns the methodology of the literature assessment. The manuscript provides the search terms and the total number of publications, but some essential additional information is missing: When was the Web of Science search performed? Which publication types were considered? Have you applied any language or location restrictions? Did you check the classifications independently and manually (or at least a sample of it)? I do not think you need to provide a very detailed protocol for this short communication, but one or two additional sentences may be helpful.
My third point concerns the use of citation rates as an argument for Ep/P. The statement that this definition "leads to more impactful geoscience" is not really supported by the numbers. Citation rates differ between research fields, publication year, journal, etc. and may also be impacted by individual highly cited studies. I suggest removing that argument.
Minor comments
Line 54: What do you mean by "Man in the Biosphere Program"?
Line 80: I don't really get the meaning of that sentence. Consider revising it.
Line 100: I suggest replacing "leads to more impactful geoscience" with a neutral framing (see my comment above).
Line 119: In my opinion, the wording "severe errors" may be too strong. Consider using more cautious wording.
Line 136: "Preformed" should "be performed"