Great Basin Desert
The Great Basin Desert is part of the Great Basin between the Sierra Nevada and the Wasatch Range in the western United States. The desert is a geographical region that largely overlaps the Great Basin shrub steppe defined by the World Wildlife Fund, and the Central Basin and Range ecoregion defined by the U.S. Environmental Protection Agency and United States Geological Survey. It is a temperate desert with hot, dry summers and snowy winters. The desert spans large portions of Nevada and Utah, and extends into eastern California. The desert is one of the four biologically defined deserts in North America, in addition to the Mojave, Sonoran, and Chihuahuan Deserts.
Basin and range topography characterizes the desert: wide valleys bordered by parallel mountain ranges generally oriented north–south. There are more than 33 peaks within the desert with summits higher than, but valleys in the region are also high, most with elevations above. The biological communities of the Great Basin Desert vary according to altitude: from low salty dry lakes, up through rolling sagebrush valleys, to pinyon-juniper forests. The significant variation between valleys and peaks has created a variety of habitat niches which has in turn led to many small, isolated populations of genetically unique plant and animal species throughout the region. According to Grayson, more than 600 species of vertebrates live in the floristic Great Basin, which has a similar areal footprint to the ecoregion. Sixty-three of these species have been identified as species of conservation concern due to contracting natural habitats.
The ecology of the desert varies across geography also. The desert's high elevation and location between mountain ranges influences regional climate: the desert formed by the rain shadow of the Sierra Nevada that blocks moisture from the Pacific Ocean, while the Rocky Mountains create a barrier effect that restricts moisture from the Gulf of Mexico. Different locations in the desert have different amounts of precipitation depending on the strength of these rain shadows. The environment is influenced by Pleistocene lakes that dried after the last ice age: Lake Lahontan and Lake Bonneville. Each of these lakes left different amounts of salinity and alkalinity.
Definition and boundaries
The Great Basin Desert is defined by its animals and plants, yet the boundaries are unclear.Scientists have different definitions of the Great Basin Desert, which are often defined by negatives. J. Robert Macey defines the "Great Basin scrub desert as lacking creosote bush." The Great Basin Desert includes several arid basins lacking Larrea tridentata such as the "Chalfant, Hammil, Benton, and Queen valleys," as well as all but the southeast portion of the Owens Valley. Conversely, the "Panamint, Saline, and Eureka valleys" have creosote bush, unlike the Deep Springs Valley which includes part of the Great Basin scrub desert.
The study and definition of ecoregions can also indicate the boundaries of the Great Basin Desert. In 1987 J.M. Omernik defined a desert ecoregion between the Sierra Nevada and Wasatch Range, naming it the "Northern Basin and Range" ecoregion. In 1999, the U.S. EPA renamed the "Northern Basin and Range" the "Central Basin and Range" and the " High Desert" the "Northern Basin and Range". The World Wildlife Fund adopted the Basin and Range ecoregions from Omernik, but excised a small region of high-altitude areas which contain Holocene refugia, from the former "Northern Basin and Range" ecoregion and renamed it the "Great Basin Shrub Steppe". Although the EPA had refined the boundaries of the Central Basin and Range ecoregion by 2003, when USGS geographer Christopher Soulard wrote his reports on the region, his maps used the 1999 boundary for the "Central Basin and Range", which is essentially the same as the "Great Basin Shrub Steppe". He states that the Great Basin Desert is "encompassed within" that area.
This article describes the general ecology of the region, including the high-elevation areas, and does not rely on minor differences in the definitions of the ecoregion or desert. See Great Basin montane forests for more specific details on the high-elevation ecoregion.
Climate
The climate of the Great Basin desert is characterized by extremes: hot, dry summers and cold, snowy winters; frigid alpine ridges and warm, windy valleys; days over followed by nights near. This is the climate of the high desert.The Great Basin desert climate begins with the Sierra Nevada in eastern California. Rising above sea level, this mountain range casts a large rain shadow over the desert. Weather coming in from the Pacific Ocean quickly loses its moisture as rain and snow as it is forced up and over the steep mountains. By the time it reaches the east side of the mountains, little moisture is left to bring to the desert. The rain shadow effect is more pronounced closer to the Sierra Nevada, with yearly precipitation in the Great Basin desert averaging in the west and inches in the east. Moisture that manages to reach the ecoregion tends to precipitate as rain and snow in higher elevations, primarily over the region's long, parallel mountains. Ultimately, any precipitation that falls within the desert fails to drain either to the Atlantic Ocean or to the Pacific Ocean. Instead, precipitation drains to ephemeral or saline lakes via streams, or disappears via evaporation or absorption into the soil. The desert is the coldest of the deserts in North America.
File:Rainshadow.gif|thumb|upright=1.35|Orographic uplift resulting in a rain shadow as air descends and compresses, resulting in arid warming on the leeward side of a mountain
On any given day, the weather across the Great Basin desert is variable. The region is extremely mountainous, and the temperatures vary depending on the elevation. In general, temperature decreases 3.6 degrees F for every 1000 feet gained in elevation. This translates to as much as a difference between mountaintops and valley floors on the same day at the same time. In the heat of summer this difference can be even more pronounced. With some exceptions wind generally increases with elevation or altitude and thus strong winds are often encountered on mountain tops and ridges.
This dry climate and rugged topography proves too harsh for many plant and animal species; however, genetic adaptations to these conditions have led to reasonably high species richness within the ecoregion.
The Great Basin National Park, located in a central part of the Great Basin desert, provides perhaps the best example of a typical climate for the region.
Fallon's climate is typical of lower elevations in the western part of the Great Basin desert. Located in the Forty Mile Desert, precipitation is rare, and summers are hot, though temperatures are more moderate than those in deserts like the Mojave and Sonoran, due to the region's higher elevation and latitude. Winters in this section of the basin are still cold, however.
The Great Salt Lake Desert, located near the northeast corner of the Great Basin desert, is an excellent example of a cold desert climate. Although still arid, it is worthy to note that this portion of the desert receives more precipitation than the similar playas and salt pans on the western edge of the Great Basin desert.