Geoscience Reference
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nine
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e Great “Medieval Drought”
When we move beyond Europe and the North Atlantic into
drier environments and lands with unpredictable rainfall, we
enter a Medieval world where drought cycles and even a few
inches of rain could make all the dif erence between life and
death. While Europe basked in summer warmth and the Norse
sailed far west, much of humanity suf ered through heat and
prolonged droughts. Archaeology and climatology tell us that
drought was the silent killer of the Medieval Warm Period, a
harsh reality that challenged human ingenuity to the limit.
Brian Fagan, h
e Great Warming
The cool, moist conditions of the Neoglacial period ended in the
late Holocene, with the climate becoming drier and warmer beginning about
1,850 years ago and continuing for more than 1,000 years. Although the gen-
eral trend in climate in the modern-day western United States was toward
dryness, conditions also became more variable: prolonged droughts were
interspersed with sudden excursions of extreme wetness. h e paleoclimate
record of the past 1,800 years contains many examples of such climate swings,
and, though both ends of the climate spectrum are of concern, it is the pros-
pect of extended drought that most worries water planners in the West today.
A period that included episodes of extended and severe dryness began in
about AD 900 and lasted until about AD 1400. Sometimes referred to as the
“Medieval drought” in the western United States, this period was marked (in
some regions of the West) by two prolonged “megadroughts” separated by a
wet interval around AD 1100-1200. h ese droughts are considered by many
paleoclimate investigators as possible analogs of the protracted droughts the
West could face in the future and, as such, they provide an important impe-
tus for water sustainability planning.
We begin this chapter by looking at the demise of the Ancestral Pueblo
civilization in the Southwest, which occurred near the end of the Medieval
drought period. h
is example shows how the megadroughts af ected early
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