March 19, 2012

A drought that began in Mexico in 2010 has turned into the worst that the country has experienced since official weather record keeping began in 1941, according to Mexican officials. At least two-thirds of Mexico’s 31 states are experiencing extremely dry conditions with below-normal rainfall. The north-central states of Coahuila, Durango, San Luis Potosi, and Zacatecas have been hardest hit. However, government officials are also concerned about drought in Guanajuato, one of the top food-producing states in the country. Mexican farmers produce large quantities of beans, corn, onions, and tomatoes, both for export and as food for their own people. Mexico is also the chief supplier of cattle to the United States. According to some estimates, food production across Mexico has fallen by 40 percent, raising food prices.

(World Book map; map data © MapQuest.com, Inc.)

Farmers who rely on rainfall to water their crops and livestock were the first to experience hardship. Rain has fallen in some states at only half the usual levels. As the dry conditions have continued, lakes and reservoirs have fallen to critically low levels. Many farmers are no longer able to irrigate their crops, and ranchers cannot supply their cattle with water. Several towns have run out of drinking water. The government has begun delivering emergency food and water supplies to thousands of people, and about 2 million others lack adequate food.

Some meteorologists expect the drought to continue for at least several more months. They believe the dry spell is the result of a La Nina. A La Nina is a weather phenomenon in which the waters of the eastern Pacific Ocean become colder and the climate becomes drier. A La Nina follows the better-known weather condition known as an El Nino. During an El Nino, waters of the eastern Pacific Ocean become warmer and the climate becomes wetter. One of the strongest La Nina’s in more than 10 years occurred from 2010 to 2011. Texas has also been experiencing a severe drought.

Additional World Book article:

• Food supply

March 16, 2012

Spring weather has come early to the United States, according to meteorologists at the National Oceanic and Atmospheric Administration (NOAA). On March 14, 400 locations around the United States reported record highs. Even the 68 °F (20 °C) temperature at Duluth, Minnesota, which was far below the 80 °F (27 °C) reported in Miami, Houston, and Chicago, was 35 Farhrenheit degrees (19 Centigrade degrees) above average.

Spring 2012 is following the fourth-warmest U.S. winter since record keeping began in 1895. Unseasonably warm temperatures have resulted in such welcome developments as lower natural gas heating costs for consumers, as well as concerns among farmers that spring frosts may damage crops that produce buds this early.

Because of the early arrival of spring in the United States, the famous cherry blossoms that tourists flock to the nation's capital to see are expected to bloom early. (Courtesy Dean Brown from Nancy Palmer)

The winter of 2012, which meteorologists define as the period from Dec. 1, 2011, to Feb. 29, 2012, brought no major snowstorms to the United States. Snow cover in early March, as photographed by NASA’s Terra Earth observing satellite, was much spottier and less thick than the snow cover recorded for the same time in 2011.

The less extensive snow cover, according to NOAA scientists, has lowered the risk of spring flooding. For the first time in four years, no area in the United States was expected to experience major spring flooding, according to an agency report released on March 15. At this time in 2011, half the country was at above-average risk of flooding.

According to meteorologists, the warm spring weather may be the result of two climate patterns in effect in 2012. One is a La Nina, during which cooler-than-normal water temperatures in the eastern Pacific Ocean produce warmer-than-normal temperatures and drier conditions in much of the United States. A strong La Nina has been in effect throughout 2011 and is just beginning to dissipate. Another weather pattern affecting U.S. climate is the Arctic Oscillation (AO). That phenomenon, in which changes in air pressure affect the circulation of warm and cold air masses in the upper atmosphere, has been bottling up cold Arctic air in regions around the North Pole.

Will the warm weather continue? NOAA forecasters indicate that temperatures for the rest of March, April, and May will probably be about one Fahrenheit degree (0.6 Centigrade degree) above normal. Nevertheless, one or two extreme temperature fluctuations during that period remain possible.

Additional World Book articles:

• Global warming
• Ocean (How the ocean moves)

March 9, 2012

Days of very heavy rain in Australia have caused flooding in parts of three states, New South Wales (NSW), Queensland, and Victoria. Thousands of residents have been forced to evacuate in NSW, where an enormous stretch–fully 75 percent–of Australia’s most populous state is under water. In what has been described as the state’s worst flooding in 150 years, scores of towns are inundated–from Forbes in central NSW to Griffith in the south and across the state line into northern Victoria. On March 7, the heaviest recorded rainfall in years triggered flash flooding across much of Sydney, Australia’s largest city.

World Book map; map data © MapQuest.com, Inc.

La Nina weather conditions, which typically bring higher-than-normal rainfall, are affecting Australia’s southeast. “Australia is in the throes of two consecutive La Nina events,” stated Aaron Coutts-Smith, NSW climate manager for Australia’s Bureau of Meteorology. “It is very rare to have such persistent, record-breaking rainfall over such large areas .  .  .”  Just weeks ago, in February, thousands were forced to evacuate in Queensland, where residents suffered through a third major flood in less than two years. From 2001 through 2009, the same area, Australia’s southeast, underwent the worst drought in the continent’s recorded history.

Additional World Book articles

• Australia 2006 (Back in Time article)
• Australia 2007 (Back in Time article)
• Australia 2008 (Back in Time article)
• Australia 2009 (Back in Time article)
• Australia 2010 (Back in Time article)
• Australia 2011 (Back in Time article)