Geoscience Reference
In-Depth Information
3 Key Findings
The calibration of the regression model within the full 1876 AD to 2004 AD and
two split periods, the number of living oak trees, RBar and the EPS is shown in
Fig. 1 a, b. The corresponding patterns of TRW and measured seasonal precipitation
sum for the calibration period is displayed. The reconstruction of Holocene summer
precipitation variability between 3250 BC and 2250 BC is displayed in Fig. 2 .
The raw TRW (Fig. 2 a) of the MR dropped between 2750 BC and 2731 BC and
shows a strong increase later on. This period is framed by a strong decrease in
replication stretching from around 2800 BC to 2650 BC (Fig. 2 b). The precipitation
reconstruction (Fig. 2 c) shows a drop for the period from 2746 BC to 2727 BC
which did not occur at another time during the researched period. Prior to this
period an elevated number of severe wet (>2
) summers occurred which was
followed by roughly 170 years where severely dry (<
) summers had been
reconstructed. These
findings might indicate a changing hydrodynamic activity
around 2750 BC. In addition a period of high
flood frequency from 2991 BC to
2693 BC can be identi
flood events coincided with years where the
reconstruction shows high precipitation (>1
ed. 10 of 30
); see Fig. 2 a.
The increase in raw TRW (Fig. 2 a), which is uncommon in the HOC until that
time (Friedrich et al. 2004 ), can be interpreted as a signal for changing forest
dynamics (Spurk et al. 2002 ). Spurk et al. ( 2002 ) explain the raw TRW increase as
phase of succession which might follow a period of wetter than normal climate
which suppressed germination due to a change in climate to more suitable growing
Fig. 1 Relation between TRW index and seasonal precipitation for the MR. a Synchronicity
between TRW index (black) and precipitation sum of April 1st to July 10th (blue) for the MR over
the full period (1876 AD to 2004 AD) and two split periods. Year to year precipitation variability
finds good expression in TRW index. From historical data there is only one medium winter ood
event known (blue bar, 1909 AD), however no WAA had been found for this event (see text
below). b Number of living oak trees used to develop the TRW index (grey filled area), RBar
(grey) and EPS (black). Values for RBar and EPS indicate high common signal strength
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