Arizona

The last of the contiguous states admitted to the Union, Arizona is part of both the southwest and [Page 75]the mountain west, with a hot, dry desert climate in much of the state—Phoenix, the capital and largest city, is the hottest metropolitan area in the country—but cooler weather dominates in the mountain ranges and forests of the north. Only about 15 percent of the state is privately owned. More than a quarter of the state is federal land occupied by numerous Native American tribes, including the home of the Navajo Nation and the Hopi tribe. The remainder is state trust land, parkland, and public forest.

Only 364 sq. mi. (942 sq. km) of the state's 113,998 sq. mi. (295,253 sq. km) is covered with water, and precipitation comes mainly in the form of moist winds from the Gulf of Mexico and the Gulf of California, which bring summer rains from July to September, with infrequent flash floods. Annual precipitation is about 10 in. (25 cm) in the Colorado Plateau in the northeast, less in the desert. The mountains sometimes see heavy snowfall when cold air masses come in from Canada, and the Colorado Plateau has much cooler summers than the rest of the state. Temperature swings can be extreme, and a 50 degree F (27 degree C) difference between day and night in rural areas is not uncommon in the summer.

Arizona originally possessed more arable land and received more rainfall. It has desertified over time, in part because of human land use and climate change. The original settlement of the area was prompted by the vast agricultural potential of the land. The warm climate continues to assist the state's agricultural sector, allowing it to produce crops long after it has become too cold in much of the rest of the country, but water crises and wildfires are perennial problems.

The 1992 Colorado River Compact requires that 8.23 million acre-ft. of water are released from the Colorado River every year to Nevada, California, and Mexico, which in 2002 led to a conflict between the owners of the Colorado River water rights and the California cities downriver. The federal government eventually ruled that the water provided for in the compact was only excess water that the owners didn't require, and that California was required to equitably divide the water it received.

The future of Arizona's climate is unclear, but higher temperatures are predicted by most models, increasing by more than 6 degrees F (3.3 degrees C) over the course of the 21st century in some models. Decreased snow accumulation in the mountains both in Arizona and further north could lead to water shortages and reduce the flow to streams and creeks, drying them up in the warm months. Already, significant increases in wildfires have been seen, much as in California and Texas. The state's largest wildfire in history raged over half a million acres from Memorial Day weekend 2011 through the summer, spreading into New Mexico and greatly increasing the chances of flash floods in the fall. The Wallow Fire started in a campground and expanded through numerous Arizona mountain towns, at the same time that another 100,000-acre wildfire was already burning elsewhere in the state.

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