The Influence of Elevation on a Location's Climate
Image courtesy of author.
When it comes to the climate characteristics of a specific location, latitude is a common and fundamental factor. In general, a location's proximity to the equator (0° latitude) can offer a basic sense of what type of climate one might expect simply due to geometry. The lower the latitude, the greater the annual solar exposure. More solar radiation means more thermal energy (i.e., heat). Think of this way: would you rather take a summer beach vacation at 15°N or 80°N latitude?
But this is only one of three coordinates. Any location on Earth entails both latitude and longitude coordinates. Though, the proximity from the prime meridian (0° longitude) is largely inconsequential regarding solar exposure.
The third coordinate regards height relative to sea level—this is called the elevation. If latitude is the x-coordinate and longitude is the y-coordinate, then elevation represents the z-coordinate. As such, the implications of elevation on a location's climate have less to do with geometry and more to do with physics. Elevation can play a crucial role in shaping a location's climate through the following influences:
Higher elevation, less atmospheric pressure
Air pressure diminishes at higher elevations due to the thinning of the atmosphere. Atmospheric pressure, also known as air pressure or barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. At sea level, standard air pressure is 1013.25 millibars. Denver, Colorado, which is nicknamed the "Mile High City", is located at an elevation of around 5,300 feet above sea level (1 mile = 5,280 feet), leading to a lower atmospheric pressure at around 850 millibars. Mt. Denali, Alaska, at 20,310 feet (the highest peak in North America) may have an atmospheric pressure around 450 millibars.
For reference, at an altitude of 30,000 feet, the air pressure outside of an airplane may be around 300 millibars. It is also worth distinguishing between elevation and altitude. Elevation can be defined as the vertical distance of a location on Earth relative to sea level. Altitude can be defined as the vertical distance between an object and the Earth's surface.
Higher elevation, less humidity
The thinning of the atmosphere at higher elevations means less air molecules. The air is less dense. This will result in proportionately less oxygen (which is why it is more taxing on the lungs to do heavy cardiovascular exercise at higher elevations). Higher elevations also result in less humidity as cooler temperatures reduce the air's capacity to hold moisture, leading to generally drier conditions.
Higher elevation, lower temperature
As elevation increases, air expands and atmospheric pressure decreases, which also results in lower air temperatures. This phenomenon is referred to as the adiabatic lapse rate, which has been approximated at a decrease of about 5.4 degrees Fahrenheit per 1,000 feet above sea level.
Be sure to consider the geographic context
Of course, a dynamic interplay of these factors and myriad other influences will cultivate the specific conditions at any given time and location. For instance, consider the role that the elevations of surrounding landforms can have on a given location. Geographic context can affect precipitation through orographic lift, a phenomenon by which moist air masses are forced upward by mountain ranges; then, as the air rises, it cools and condenses. As a result, the windward size of a mountain will receive more precipitation and the leeward side will experience drier conditions—referred to as a rain shadow effect.
The unique mix of factors for any given location warrants a careful consideration of context in order to more accurately understand the general climate characteristics of any given location.
Cities may feature a wide range elevations, choose climate data wisely
In many instances, it may seem obvious that the closest weather station to a given location is the most representative for a climate data analysis. This is not necessarily the case. Some cities exhibit a vast range in elevations. Latitude and longitude only tell part of the story. A more complete evaluation should consider elevation—both of the specific location and its geographic context.
Elevations of various U.S. cities. Figure by Daniel Overbey. |
