Lower Colorado River Basin

Below, you can follow a raindrop through the Colorado River, including the Lower Colorado River Basin, on its way from White Hills, Arizona to the Golfo de California (the Gulf of California).

Level I Ecoregions are the 15 broad ecological classifications across North America (US EPA, 2015). These broad classifications allow for determining the intercontinental ecological patterns and are labeled as: Arctic Cordillera, Tundra, Taiga, Hudson Plains, Northern Forests, Northwestern Forested Mountains, Marine West Coast Forests, Eastern Temperate Forests, Great Plains, North American Deserts, Mediterranean California, Southern Semi-Arid Highlands, Temperate Sierras, Tropical Dry Forests and Tropical Wet Forests (US EPA, 2015). The Level I Ecoregions are easily distinguished from each other yet contain a high level of variability within them (Omernik & Griffith, 2014).

 _{US EPA, O. (2015). Ecoregions of North America.  https://www.epa.gov/eco-research/ecoregions-north-america    Omernik, J. M. & Griffith, G. E. (2014). Ecoregions of the Conterminous United States:   Evolution of a Hierarchical Spatial Framework. Environmental Management. DOI: 10.1007/s00267-014-0364-1}  

• The Lower Colorado River Basin lies in the North American Desert classification of the Level I Ecoregions, which is characterized by its unique aridity, low-lying shrub, grass and cactus vegetation, lack of trees, and generally lower elevation compared to the surrounding ecoregions (Commission for Environmental Cooperation, 1997).
  • According to the Commission for Environmental Cooperation (1997), North American Deserts' general physical characterizations are plains with hills, plains with mountains, and tablelands of high relief; the southern mountain ranges are smaller than the northern ones; wind and water erosion of sedimentary rock has left behind vast canyons, cliffs, buttes, and mesas; the soil is dry and lacks in organic matter and distinct soil profiles, and sand dunes are common (Commission for Environmental Cooperation, 1997).
  • Concerning the climate zone of the Lower Colorado River Basin, which is a subtropical desert, the Level I Ecoregion designation closely resembles the climate zone with 130mm - 380mm (5.1in - 15in) of precipitation with extreme temperatures (Commission for Environmental Cooperation, 1997). This is in the character of the subtropical desert climates, which experience very high temperatures in the summer months with only 2-8 inches of precipitation annually.
  • As for the biological factors of the area, most of the northern low-lying vegetation has been converted into agricultural areas, with a low presence of large mammals (the large mammals in the area include mule deer, pronghorn antelope, coyotes, bobcats, and badgers) (Commission for Environmental Cooperation, 1997).

 _{Commission for Environmental Cooperation. (1997). Ecological Regions of North America Toward}  a Common  _{Perspective. Communications and Public Outreach Department.    http://www.cec.org/files/documents/publications/1701-ecological-regions-north-america-toward-common-perspective-en.pdf}  

An anthropogenic biome, or anthromes (also known as human biomes), as described by NASA's Socioeconomic Data and Applications Center (n.d.), are the terrestrial ecological regions in their human-altered form and are defined by consistent human interaction. There are 21 specific anthromes which are differentiated by population density, land use, and vegetation and are grouped into distinct six categories, which are dense settlements, villages, croplands, rangeland, forested, and wildlands (Socioeconomic Data and Applications Center, n.d.).

 _{Socioeconomic Data and Applications Center. (n.d.). Anthropogenic Biomes. NASA.  https://sedac.ciesin.columbia.edu/data/collection/anthromes}  

• Within the Lower Colorado River Basin, there are nine distinct anthromes, which, in order of most present to least, are:
  • Remote Rangeland: Areas with livestock grazing, minimal crops and forests, and inconsequential human populations (Ellis and Ramankutty, 2008).
  • Populated Rangeland: Areas with livestock grazing, minimal crops and forests, and minor human populations (Ellis and Ramankutty, 2008).
  • Residential Rangeland: Areas with livestock grazing, minimal crops and forests, and substantial human populations (Ellis and Ramankutty, 2008).
  • Populated Irrigated Cropland: Areas with annual crops mixed with other land uses and land covers that are irrigated with minor human populations (Ellis and Ramankutty, 2008).
  • Residential Irrigated Cropland: Areas with annual crops mixed with other land uses and land covers that are irrigated with substantial human populations (Ellis and Ramankutty, 2008).
  • Cropped and Pastoral Villages: Dense agricultural settlements with a mix of crops and pasture (Ellis and Ramankutty, 2008).
  • Remote Cropland: Areas with annual crops mixed with other land uses and land covers with inconsequential human populations (Ellis and Ramankutty, 2008).
  • Barren: Land without human populations or agriculture with no tree cover and are mostly deserts and frozen land (Ellis and Ramankutty, 2008).
  • Urban: Dense settlements with a substantial urban area and densely built environments with very high human populations (Ellis and Ramankutty, 2008).

 _{Erle C Ellis and Navin Ramankutty. (2008). Putting people in the map: anthropogenic biomes of the world. The Ecological Society of America. 10.1890/070062}