
Tree Rings Reveal Droughts El Malpais National Monument, in west central New Mexico, has pockets of vegetation that have been surrounded by lava fields for about 3,000 years, so they have escaped wildfires, grazing animals, agricultural activity, and logging. Henri Grissino-Mayer generated a 2,129-year annual precipitation record using tree ring data from living and dead trees in this park (FIGURE 27.22).
FIGURE 27.22 Annual precipitation record for 2,129 years, inferred from compiled tree ring data in El Malpais National Monument, New Mexico. Data were averaged over 10-year intervals; the graph correlates with other indicators of rainfall collected in all parts of North America. PDSI, Palmer Drought Severity Index: 0, normal rainfall; increasing numbers mean increasing excess of rainfall; decreasing numbers mean increasing severity of drought.
* A severe drougt contributed to a series of catastrophic dust storms that turned the midwestern United States into a "dust bowl" between 1933 and 1939.
Around a.d.770, the Mayan civilization began to suffer a massive population loss, particularly in the southern lowlands of Mesoamerica. The El Malpais tree ring data show a drought during that time. Was it more or less severe than the Dust Bowl drought in 1933–1939?

To determine: Whether the drought at A.D. 770 was more or less severe than the Dust Bowl drought in 1933-1939.
Concept introduction: Tree rings are the number of concentric rings in the cross section of the tree trunks that represent a single year growth. Tree ring dating is done to find the exact year of their formation. Tree ring dating helps to analyze the atmospheric condition during the different periods in history. The researchers have created the record of drought dating back hundreds to thousands of years by using tree rings.
Explanation of Solution
The Mayan civilization suffers a massive population loss in the 770 AD. Between 1933 and 1939, a severe drought contributed to the series of the catastrophic dust storms that turned the Midwestern Unites States into a dust bowl. From the data, there is a point that extends to about -1.5 PDSI at 770 A.D. It indicates a severe drought. The dust bowl drought which is indicated by a * on the graph has a PDSI of about -1. Comparing to the drought at 770 A.D. it was more severe than the dust bowl.
The drought in the 770 A.D. was more severe than the drought during the dust bowl.
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