The Influence of The Intertropical Convergence Zone
Many factors influenced the Maya climate throughout the Holocene period, however one of the most significant components we use in examining the Maya collapse is the Intertropical Convergence Zone and its' patterns of change over time.
Throughout history, the Intertropical Convergence Zone, or the ITCZ, has put great environmental stress on not only the early Maya civilization, but also on other regions in similar latitudes around the world. The ITCZ is a region encircling the globe near the equator where the southeastern and northeastern trade winds meet, creating bands of clouds and tropical storms. This meeting zone generates low-pressure pockets and high levels of precipitation that accounts for most of the annual rainfall for the various regions affected by this zone.( Paterson, Haug, 2013) Climate variability in this region was undoubtedly driven by the annual southern shifts of the ITCZ's position, drying out the environment and bringing intense trade winds.
The Annual Pattern of the ITCZ
During the summer and fall months, usually beginning around June or July when the ITCZ is at its' northern most latitudinal position over the Cariaco Basin, the region receives almost all of its' annual rainfall. These are crucial months for the Maya in collecting and storing water to be used for agricultural purposes and for the growing Maya population. As the seasons change brings the winter and spring months, the ITCZ makes its' annual southern shift below the equator, bringing strong trade winds that quickly dry out the region.
This dependency on the ITCZ for the majority of the region's rainfall made the Maya very vulnerable to periods of drought brought on by the dry winter months, and even more vulnerable to the ITCZ's long-term patterns of change. Scientists draw conclusions and gather data of the ITCZ and its' patterns of change using ancient sediment, paleo-climate, and historical records, and as many note, there is a clear record of the seasonal migration of the ITCZ preserved in the elemental composition of the sediment in the Cariaco Basin. ( Haug, Hughen, Sigman, Peterson, Rohl, 2013 ) It is through these results that it becomes clear that a gradual decrease in rainfall and a gradual increasing of periods of intense drought began to take not only an environmental toll, but also a social toll on the Maya people.
This dependency on the ITCZ for the majority of the region's rainfall made the Maya very vulnerable to periods of drought brought on by the dry winter months, and even more vulnerable to the ITCZ's long-term patterns of change. Scientists draw conclusions and gather data of the ITCZ and its' patterns of change using ancient sediment, paleo-climate, and historical records, and as many note, there is a clear record of the seasonal migration of the ITCZ preserved in the elemental composition of the sediment in the Cariaco Basin. ( Haug, Hughen, Sigman, Peterson, Rohl, 2013 ) It is through these results that it becomes clear that a gradual decrease in rainfall and a gradual increasing of periods of intense drought began to take not only an environmental toll, but also a social toll on the Maya people.
What Changed?
Throughout their history, the Maya people had made cultural adaptions to this annual shifting of the ITZC, however what they could not adapt to was the gradual southern shift in the average position of the ITCZ over time.
During the late Holocene, "after about 5ka, decreasing summer isolation in the Northern Hemisphere and resulting southward movement of the average position of the ITCZ causes a decline in southeasterly winds."(Poore, Quinn, Verardo, 2004) This decrease of southeasterly winds led to a decline in the northern latitudinal range of the ITCZ, and over time, the average position failed to reach its' former northern position over the Maya lowlands. To the Maya, this climatic change had harsh consequences on rainfall patterns during the crucial summer and fall months that brought about almost all of the region's annual rainfall. Without the traditional pattern of the ITCZ, the Maya began to receive less amounts of rainfall each year. As periods of extensive drought intensified, the people were left very vulnerable to water shortages.
Without the consistent amounts of annual rainfall their society once thrived on, they Maya became heavily reliant on other natural water resources. Eventually the growing Maya populations began to surpass their sustainability thresholds, forcing the mass depopulation of major Maya cities.
Without the consistent amounts of annual rainfall their society once thrived on, they Maya became heavily reliant on other natural water resources. Eventually the growing Maya populations began to surpass their sustainability thresholds, forcing the mass depopulation of major Maya cities.
IMAGE SOURCE: http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=4028;
http://en.wikipedia.org/wiki/Intertropical_Convergence_Zone,
http://en.wikipedia.org/wiki/File:Vindhya.jpg
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