 | The examples and perspective in this article deal primarily with North America and do not represent a worldwide view of the subject.(February 2023) |
A megadrought is an exceptionally severe drought, lasting for many years and covering a wide area.
| The examples and perspective in this article deal primarily with North America and do not represent a worldwide view of the subject.(February 2023) |
A megadrought is an exceptionally severe drought, lasting for many years and covering a wide area.
There is no exact definition of a megadrought. [2] The term was first used by Connie Woodhouse and Jonathan Overpeck in their 1998 paper, 2000 Years of Drought Variability in the Central United States. [2] [3] In this, it referred to two periods of severe drought in the US – one at the end of the 13th century and the other in the middle of the 16th century. [3] The term was then popularised as a similar severe drought affected the Southwestern US from the year 2000. [2]
Benjamin Cook suggested that the definition be a drought which is exceptionally severe compared to the weather during the previous 2,000 years. [2] This was still quite imprecise and so research has suggested quantitative measures based on a Standard Precipitation Index. [4]
Past megadroughts in North America have been associated with persistent multiyear La Niña conditions (cooler than normal water temperatures in the tropical eastern Pacific Ocean). [5]
Megadroughts have historically led to the mass migration of humans away from drought affected lands, resulting in a significant population decline from pre-drought levels. They are suspected of playing a primary role in the collapse of several pre-industrial civilizations, including the Ancestral Puebloans of the North American Southwest, [6] the Khmer Empire of Cambodia, [7] the Maya of Mesoamerica, [8] the Tiwanaku of Bolivia, [9] and the Yuan Dynasty of China. [10]
The African Sahel region in particular has suffered multiple megadroughts throughout history, with the most recent lasting from approximately 1400 AD to 1750 AD. [11] North America experienced at least four megadroughts during the Medieval Warm Period. [12]
There are several sources for establishing the past occurrence and frequency of megadroughts, including:
The Little Ice Age (LIA) was a period of regional cooling, particularly pronounced in the North Atlantic region. It was not a true ice age of global extent. The term was introduced into scientific literature by François E. Matthes in 1939. The period has been conventionally defined as extending from the 16th to the 19th centuries, but some experts prefer an alternative time-span from about 1300 to about 1850.
In the study of past climates ("paleoclimatology"), climate proxies are preserved physical characteristics of the past that stand in for direct meteorological measurements and enable scientists to reconstruct the climatic conditions over a longer fraction of the Earth's history. Reliable global records of climate only began in the 1880s, and proxies provide the only means for scientists to determine climatic patterns before record-keeping began.
The Sahel region of Africa has long experienced a series of historic droughts, dating back to at least the 17th century. The Sahel region is a climate zone sandwiched between the Sudanian Savanna to the south and the Sahara desert to the north, across West and Central Africa. While the frequency of drought in the region is thought to have increased from the end of the 19th century, three long droughts have had dramatic environmental and societal effects upon the Sahel nations. Famine followed severe droughts in the 1910s, the 1940s, and the 1960s, 1970s and 1980s, although a partial recovery occurred from 1975-80. The most recent drought occurred in 2012.
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Climate change in California has resulted in higher than average temperatures, leading to increased occurrences of droughts and wildfires. Over the next few decades in California, climate change is likely to further reduce water availability, increase wildfire risk, decrease agricultural productivity, and threaten coastal ecosystems. The state will also be impacted economically due to the rising cost of providing water to its residents along with revenue and job loss in the agricultural sector. Economic impacts also include inflation from rising insurance premiums, energy costs and food prices. California has taken a number of steps to mitigate impacts of climate change in the state.
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The historical and ongoing droughts in California result from various complex meteorological phenomena, some of which are not fully understood by scientists.
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The southwestern North American megadrought is an ongoing megadrought in the southwestern region of North America that began in 2000. At least 24 years in length, the drought is the driest multi-decade period the region has seen since at least 800 CE. The megadrought has prompted the declaration of a water shortage at Lake Mead, the largest reservoir in the United States. Climate change models project drier conditions in the region through the end of the 21st century, though climate change mitigation may avoid the most extreme impacts.
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Connie A. Woodhouse is a regents professor at the University of Arizona who is known for her use of tree rings to reconstruct the hydroclimate of the past, especially in western North America. In 2022 she was elected a fellow of the American Geophysical Union
Consequently, despite considerable limitations of the proxy evidence, to date it does support the idea that, during medieval times, the global hydroclimate tended towards what we would now call a La Niña-like state.
New findings suggest that a decades-long drought at about the time the kingdom began fading away in the 14th century may have been a major culprit. Evidence for a megadrought comes from centuries-old conifers that survived the Angkor era.
This far-reaching rainfall chronology also provides the first independent confirmation of the so-called Terminal Classic drought, a megadrought some anthropologists relate to the collapse of the Mayan civilization.
In medieval times the California droughts coincided roughly with a warmer climate in Europe, which allowed the Vikings to colonize Greenland and vineyards to grow in England, and with a severe dry period in South America, which caused the collapse of that continent's most advanced pre-Inca empire, the rich and powerful state of Tiwanaku, other recent studies have found.
Although the relationship between climate and societal change is complex and not necessarily deterministic, the widespread societal changes across monsoon Asia between the mid 13th to 15th centuries, which include famines and significant political reorganization within India ([Dando, 1980], [Pant et al., 1993] and [Maharatna, 1996]), the collapse of the Yuan dynasty in China (Zhang et al., 2008); Rajarata civilization in Sri Lanka (Indrapala, 1971), and the Khmer civilization of Angkor Wat fame in Cambodia (Buckley et al., 2010), strongly suggest that the MMDs may have played a major contributing role in shaping these societal changes.
As well as the periodic droughts lasting decades, there was evidence that the Sahel region has undergone several droughts lasting a century or more....The most recent mega-drought was just 500 years ago, spanning 1400 to 1750 and coinciding with Europe's Little Ice Age.
The new record sheds light on a drought-prone 400-year period between A.D. 900 and 1300. It is punctuated by four decades-long, regionwide megadroughts centered on the years 936, 1034, 1150 and 1253.
The evidence for the big droughts comes from an analysis of the trunks of trees that grew in the dry beds of lakes, swamps and rivers in and adjacent to the Sierra Nevada, but died when the droughts ended and the water levels rose. Immersion in water has preserved the trunks over the centuries.
Marine coral records from the core ENSO region of the tropical Pacific also support the concept of decadal and longer ENSO variability during the last millennium (Cobb et al., 2003), with some indication that the MCA period experienced persistent La Niña-like SST conditions that would be drought-inducing over North America.
a historic atmospheric river storm slams Southern California […] the city's wettest day since December 2004
