Droughts - Extreme Events: A Physical Reconstruction and Risk Assessment - page 34

Calendar year AD

900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000

Atmospheric CO

14 2

Maunder

Wolf Sporer 20

10
0

− 10

− 20

Wamara
drought

Nyarubanga
drought

Lapanarat -Mahlatule
drought

Political history

Colonial
history

14th C
prosperity

1st age of
prosperity

2nd age of
prosperity

40
30
20
10
0

Lithology-inferred lake depth

Diatom-inferred conductivity

30
10
3
1
0.3
0.1

900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000
Calendar year AD

Figure 2.6. Drought and rainfall history of tropical east Africa over the past
1100 years based on lake-level and salinity fluctuations of Lake Naivasha (Kenya)
(from Verschuren et al ., 2000 ).

dominated the region. After this time, few severe droughts are apparent in the
record.

Charcoal layers

Charcoal layers found in sediments are often a reflection of severe bush-
fires. If humans can be eliminated as the cause of these fires then it is likely
that they occurred in response to drier than normal conditions. If the environ-
ment is one that is normally quite moist and rainforest or other humid climate
vegetation usually exists, then the charcoal layers may be indicative of episodes
of severe climatic drying and hence droughts. This could especially be the case
where the environment is not normally prone to bushfires and it takes a severe