Orography is the study of the topographic relief of

mountains A mountain is an elevated portion of the Earth's crust, generally with steep sides that show significant exposed bedrock. Although definitions vary, a mountain may differ from a plateau in having a limited summit area, and is usually higher th ...

, and can more broadly include hills, and any part of a region's elevated terrain. Orography (also known as ''oreography'', ''orology'' or ''oreology'') falls within the broader discipline of

geomorphology Geomorphology (from Ancient Greek: , ', "earth"; , ', "form"; and , ', "study") is the scientific study of the origin and evolution of topographic and bathymetric features created by physical, chemical or biological processes operating at or ...

. The term orography comes from the Greek: , hill, , to write.

Uses

Mountain ranges and elevated land masses have a major impact on global climate. For instance, the elevated areas of East Africa substantially determine the strength of the Indian monsoon.Srinivasan, J., Nanjundiah, Ravi S. and Chakraborty, Arindam (2005
Impact of Orography on the Simulation of Monsoon Climate in a General Circulation Model
''Indian Institute of Science'' In scientific models, such as

general circulation model A general circulation model (GCM) is a type of climate model. It employs a mathematical model of the general circulation of a planetary atmosphere or ocean. It uses the Navier–Stokes equations on a rotating sphere with thermodynamic ter ...

s, orography defines the lower boundary of the model over land. When a river's

tributaries A tributary, or affluent, is a stream or river that flows into a larger stream or main stem (or parent) river or a lake. A tributary does not flow directly into a sea or ocean. Tributaries and the main stem river drain the surrounding drain ...

or settlements by the river are listed in 'orographic sequence', they are in order from the highest (nearest the source of the river) to the lowest or mainstem (nearest the mouth). This method of listing tributaries is similar to the

Strahler Stream Order In mathematics, the Strahler number or Horton–Strahler number of a mathematical tree is a numerical measure of its branching complexity. These numbers were first developed in hydrology by and ; in this application, they are referred to as t ...

, where the headwater tributaries are listed as category 1.

Orographic precipitation

Orographic precipitation, also known as relief precipitation, is

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...

generated by a forced upward movement of air upon encountering a physiographic upland (see

anabatic wind An anabatic wind, from the Greek '' anabatos'', verbal of ''anabainein'' meaning moving upward, is a warm wind which blows up a steep slope or mountain side, driven by heating of the slope through insolation.adiabatic cooling of a rising moist air parcel may lower its temperature to its

dew point The dew point is the temperature to which air must be cooled to become saturated with water vapor, assuming constant air pressure and water content. When cooled below the dew point, moisture capacity is reduced and airborne water vapor will ...

, thus allowing for condensation of the water vapor contained within it, and hence the formation of a

cloud In meteorology, a cloud is an aerosol consisting of a visible mass of miniature liquid droplets, frozen crystals, or other particles suspended in the atmosphere of a planetary body or similar space. Water or various other chemicals may ...

. If enough water vapor condenses into cloud droplets, these droplets may become large enough to fall to the ground as precipitation. Terrain-induced precipitation is a major factor for meteorologists as they forecast the local weather. Orography can play a major role in the type, amount, intensity and duration of precipitation events. Researchers have discovered that barrier width, slope steepness and

updraft In meteorology, an updraft is a small-scale current of rising air, often within a cloud. Overview Localized regions of warm or cool air will exhibit vertical movement. A mass of warm air will typically be less dense than the surrounding regi ...

speed are major contributors for the optimal amount and intensity of orographic precipitation. Computer model simulations for these factors showed that narrow barriers and steeper slopes produced stronger updraft speeds which, in turn, enhanced orographic precipitation. Orographic precipitation is well known on oceanic

island An island (or isle) is an isolated piece of habitat that is surrounded by a dramatically different habitat, such as water. Very small islands such as emergent land features on atolls can be called islets, skerries, cays or keys. An isla ...

s, such as the

Hawaiian Islands The Hawaiian Islands ( haw, Nā Mokupuni o Hawai‘i) are an archipelago of eight major islands, several atolls, and numerous smaller islets in the North Pacific Ocean, extending some from the island of Hawaii in the south to northernmost ...

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island coun ...

, where much of the rainfall received on an island is on the windward side, and the

leeward Windward () and leeward () are terms used to describe the direction of the wind. Windward is ''upwind'' from the point of reference, i.e. towards the direction from which the wind is coming; leeward is ''downwind'' from the point of reference ...

side tends to be quite dry, almost

desert A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to denudation. About on ...

-like, by comparison. This phenomenon results in substantial local gradients of average rainfall, with coastal areas receiving on the order of per year, and interior uplands receiving over per year. Leeward coastal areas are especially dry—less than per year at

Waikiki Waikiki (; haw, Waikīkī; ; also known as Waikiki Beach) is a neighborhood of Honolulu on the south shore of the island of Oahu in the U.S. state of Hawaii. Waikiki is most famous for Waikiki Beach, which is one of six beaches in the distri ...

—and the tops of moderately high uplands are especially wet—about per year at Wai'ale'ale on Kaua'i. Another well known area for orographic precipitation is the

Pennines The Pennines (), also known as the Pennine Chain or Pennine Hills, are a range of uplands running between three regions of Northern England: North West England on the west, North East England and Yorkshire and the Humber on the east. Common ...

in the north of England where the west side of the Pennines receives more rain than the east because the clouds (generally arriving from the west) are forced up and over the hills and cause the rain to fall preferentially on the western slopes. This is particularly noticeable between

Manchester Manchester () is a city in Greater Manchester, England. It had a population of 552,000 in 2021. It is bordered by the Cheshire Plain to the south, the Pennines to the north and east, and the neighbouring city of Salford to the west. The ...

(West) and

Leeds Leeds () is a city and the administrative centre of the City of Leeds district in West Yorkshire, England. It is built around the River Aire and is in the eastern foothills of the Pennines. It is also the third-largest settlement (by popul ...

(East) where Leeds receives less rain due to a rain shadow of from the Pennines.

References

Sources

* * {{cite book, author=Whiteman, C. David, title=Mountain Meteorology: Fundamentals and Applications , publisher=Oxford University Press, year=2000, isbn=0-19-513271-8

External links

Map of the Orography of Europe
from Euratlas.com Geomorphology

Uses

Orographic precipitation

See also

References

Sources

External links