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Ecohydrology in Semi-arid and Arid Environments.

May 7, 2012

Growing up as a desert child in eastern Oregon I was raised to appreciate water as a scarce and extremely valuable resource needed for all life to flourish.  Much of the land appears desolate and lacking life to those that have not spent much time in these regions.  In the desert, plants are generally much more sparse and under much more stress for water and nutrients than more moist environments. To me this area is full of hardened, specifically adapted plants and animals that are found in hidden microenvironments. The diversity and abundance of life in these environments highly depends on water availability and the hydrologic cycle.  This blog will attempt to focus on ecohydrology in the arid regions of the western United States.

Ecohydrology has many definitions that are all based around the interaction between organisms and water in their environment.  Some of these definitions include:

  • “The study of the functional interrelations between hydrology and biota at catchment scale” and refer to the study as “a new approach to achieve sustainable management of water”  (Zalewski 1997)
  • “The sub-discipline shared by the ecological and hydrologic sciences that is concerned with the effects of hydrological processes on the distribution, structure and functioning of ecosystems, and on the effects of biotic processes on elements of the water cycle”. Nuttle (2002)
  • “Eco-hydrology implies that this science is about relationships of organisms and the hydrological component of their environment. A study should concentrate on ecology and hydrology as well as the interaction between both to deserve the adjective ‘eco-hydrologic’”. (Witte et. al. 2002)

I will be using the definition proposed by Witte et. al. throughout this blog.

photo taken summer 2010


My desert home only received about 10 inches of precipitation every year, mainly in the form of snow.  This lack of moisture created a beautiful region dominated by the presence of sagebrush and juniper trees adapted to the arid environments seen east of the Cascade Mountain Range all the way to the Rocky Mountains. This includes states such as Montana, Wyoming, Colorado, Utah, Arizona, New Mexico, Idaho, California and the eastern two thirds of Oregon and Washington. Human impacts on ecohydrology in these areas include ranching, agriculture, tourism and a bit of the technology industry (Schumann USGS).

Arid environments cover approximately one third of all land area.  The main classifications used for deserts are generally classified by the total annual amount of precipitation, annual temperature and humidity. Since the 1950’s, desert regions have mainly been divided into 3 regions based on the amount of precipitation they receive.

  1. Extremely arid lands have at least 12 consecutive months without rainfall
  2. Arid lands receive less than 250 millimeters (9.8in) of annual rainfall
  3. Semiarid lands have a mean annual precipitation between 250 (9.8in) and 500 (19.69in) millimeters. (USGS 2001).

    Photo courtesy of Oregon Climate Service

In my opinion, the best geologic part of these deserts is the mountains. The mountains appear to have more plant and animal diversity while at the same time being the cause for the surrounding arid environment. Much of the desert environment in the western United States is caused by a dual rain shadow effect and assisted by cold air pushing down from Canada. The rain shadow effect causes clouds to be pushed over mountains by orographic lifting.  This process is very similar to wringing out a sponge.  As clouds rise over mountain tops the moisture they are holding is squeezed out and without an ocean or other large water source the sponge of the cloud is left to dry. The air then continues travelling eastward down and away from the mountains to be warmed.  This warm, dry air sucks up what little moisture may be available from the land below to be deposited on the next mountains or collected until a storm builds. (USGS InfoBank). The region I grew up in, including Oregon and Washington, is special because it is subject to a dual rain shadow effect via the Coast Range and Cascade Mountain range.

Photo from Wiki Commons

This is the first post in a blog on the topic of ecohydrology in semi-arid and arid environments.   I will soon post on beetle infestation on trees and riparian area restoration in arid environments.


Bond, B. 2003. Hydrology and ecology meet and the meeting is good, Hydrological Processes, 17, 2087-2089.

Hannah, D.M., Wood, P.J. and Sadler, J.P. 2004. Ecohydrology and hydroecology: a new paradigm? Hydrological Processes. 18, 3439-3445.

Nuttle, W.K., 2002. Eco-hydrology’s past and future in focus. Eos, Transactions AGU, 83 (19), 205-212.

Porporato, A., P. D’Odorico, F. Laio, L. Ridolfi, and I. Rodriguez-Iturbe. “Ecohydrology of Water-controlled Ecosystems.” Advances in Water Resources 25.8-12 (2002): 1335-348. Web.

Schumann, Randy. “The Arid and Semi-Arid Western United States.” USGS: National Climate Change Assessment. USGS, February 2007. Web. 06 May 2012. <;.

“USGS CMG InfoBank: Rain Shadows.” Coastal & Marine Geology InfoBank. USGS, 22 Mar. 2012. Web. 06 May 2012. < moviepage/20.01.05.html>.

Walker, A. S. “What Is a Desert?” Deserts:Geology and Resources. USGS Publications Service Center, 18 Dec. 2001. Web. 06 May 2012. <;.

Witte, J.P.M., 2002. “The descriptive capacity of ecological plant species groups.” Plant Ecology, 162 (2), 199-213.

Zalewski, M., Janauer, G.A. and Jolankai, G., 1997. Ecohydrology: a new paradigm for the sustainable use of aquatic resources. Unesco, Paris. IHP-V Technical Documents in Hydrology no. 7.


3 Comments leave one →
  1. May 11, 2012 9:26 am

    I really enjoyed the “wringing out a sponge” analogy – it made that process suddenly make sense to me, despite having heard many descriptions before now that have gone over my head. Looking forward to the next article.

  2. aquilegia15 permalink
    May 12, 2012 9:17 am

    Glad I could help!

  3. February 17, 2016 1:54 am

    hi this is a great site that you have, thank u 4 sharing it with us.

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