Decades of drought, interspersed with intense monsoon rains, may have helped bring about the fall of Cambodia's ancient Khmer civilization at Angkor nearly 600 years ago, according to an analysis of tree rings, archeological remains and other evidence. The study, published this week in the journal Proceedings of the National Academy of Sciences, may also shed light on what drives—and disrupts—the rainy season across much of Asia, which waters crops for nearly half the world's population.
Scientists led by Buckley were able to reconstruct 759 years of past climate in the region surrounding Angkor by studying the annual growth rings of a cypress tree, Fokienia hodginsii, growing in the highlands of Vietnam's Bidoup Nui Ba National Park, about 700 kilometers away. By hiking high into the mountain cloud forests, the researchers were able to find rare specimens over 1,000 years old that had not been touched by loggers. After extracting tiny cores of wood showing the trees' annual growth rings, researchers reconstructed year-to-year moisture levels in this part of Southeast Asia from 1250 to 2008. The tree rings revealed evidence of a mega-drought lasting three decades—from the 1330s to 1360s-- followed by a more severe but shorter drought from the 1400s to 1420s. Written records corroborate the latter drought, which may have been felt as far away as Sri Lanka and central China.
The droughts may have been devastating for a civilization dependent on farming and an irrigation system of reservoirs, canals and embankments sprawling across more than a thousand square kilometers. The droughts could have led to crop failure and a rise in infectious disease, and both problems would have been exacerbated by the density of the population, Buckley says.
The study also finds that the droughts were punctuated by several extraordinarily intense rainy seasons that may have damaged Angkor's hydraulic system. During a normal monsoon season, Angkor's hydraulic network could have handled heavy downpours, but after extended droughts, the system may have been vulnerable to massive siltation and clogging, the study suggests. Layers of coarse debris and other sediments found blocking some canals appear to have been laid down suddenly. In other spots, apparently sudden erosion cut canals as much as 8 meters below the surrounding landscape, potentially destabilizing the hydraulic system. Archeologists have found additional evidence that canals were rebuilt and rerouted to cope with water shortages.
In compiling the longest tropical tree ring record to date, researchers found that the third-driest, and the driest, years in the last 760 years occurred back to back in 1402 and 1403, about three decades before Angkor's fall. The second driest was 1888, which coincided with the 1888-1889 El Niño, a cyclical warming of the tropical Pacific Ocean. By correlating known El Niño cycles measured with modern instruments, researchers have documented how the cyclical warming and cooling of the tropical Pacific Ocean brings rain to some places and drought to others. The authors of the current study and other researchers suggest that El Niño, possibly abetted by longer, decades-long cycles across the Pacific basin, may have played an important role in shutting down the monsoon rains in this region, creating withering droughts in the past. Some scientists suspect that warming of the global climate may intensify these cycles in the future, raising the possibility of alternating Angkor-like droughts and destructive floods that could affect billions of people.
Similar studies suggest that abrupt environmental changes may have pushed other ancient civilizations over the edge, including the Anasazi people of the southwestern United States; the Maya people of Central America, and the Akkadian people of Mesopotamia. There is some evidence that other once-powerful kingdoms in what is now Vietnam and Myanmar may have fallen during the late 1700s, following extreme dry and wet periods.
"Both human society and the erth's climate system are complex systems capable of unexpected behavior. Through the long-term perspective offered by climate and archaeological records, we can start to identify and understand the myriad ways they may interact," said study coauthor Kevin Anchukaitis, a tree ring scientist at Lamont. "The evidence from monsoon Asia should remind us that complex civilizations are still quite vulnerable to climate variability and change."Related link: An audio slideshow follows the researchers in their search for ancient trees to unlock the workings of the Asian monsoon.
Kim Martineau | EurekAlert!
Diagnoses: When Are Several Opinions Better Than One?
19.07.2016 | Max-Planck-Institut für Bildungsforschung
High in calories and low in nutrients when adolescents share pictures of food online
07.04.2016 | University of Gothenburg
Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.
"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...
In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.
A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...
By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.
"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...
COMPAMED has become the leading international marketplace for suppliers of medical manufacturing. The trade fair, which takes place every November and is co-located to MEDICA in Dusseldorf, has been steadily growing over the past years and shows that medical technology remains a rapidly growing market.
In 2016, the joint pavilion by the IVAM Microtechnology Network, the Product Market “High-tech for Medical Devices”, will be located in Hall 8a again and will...
'Ferroelectric' materials can switch between different states of electrical polarization in response to an external electric field. This flexibility means they show promise for many applications, for example in electronic devices and computer memory. Current ferroelectric materials are highly valued for their thermal and chemical stability and rapid electro-mechanical responses, but creating a material that is scalable down to the tiny sizes needed for technologies like silicon-based semiconductors (Si-based CMOS) has proven challenging.
Now, Hiroshi Funakubo and co-workers at the Tokyo Institute of Technology, in collaboration with researchers across Japan, have conducted experiments to...
14.10.2016 | Event News
14.10.2016 | Event News
12.10.2016 | Event News
21.10.2016 | Health and Medicine
21.10.2016 | Information Technology
21.10.2016 | Materials Sciences