Geoscience Reference
In-Depth Information
Sharon Nicholson attributes the precipitation
fluctuations to contraction and expansion of the
Saharan arid core rather than to north-south
shifts of the desert margin. In Australia, rainfall
changes have been related to changes in the
location and intensity of subtropical anticyclones
and associated changes in atmospheric circula-
tion. Winter rainfall decreased in southwestern
Australia while summer rainfall increased in the
southeast, particularly after 1950. Northeastern
Australia shows decadal oscillations and large
inter-annual variability.
Figure 13.12
illustrates winter and summer
fluctuations in precipitation for England and
Wales. There is wide interannual variability and
some large decadal shifts are evident. There are
also longer term changes. For example, winters
have been wetter from about 1860 onward
compared with the earlier part of the record.
Changes also depend on season - while winter
rainfall increased from 1960 to the end of the
record, summer precipitation generally decreased
over the same time. Records for individual
stations show that even over relatively short
distances there may be considerable differences
in the magnitude of anomalies, especially in an
east-west direction across the British Isles.
Winter
400
300
200
100
0
Summer
400
300
200
100
0
1750
1800
1850
1900
1950
2000
Year
Figure 13.12
Time series of winter and summer precipitation (mm) for England and Wales, 1767-1995. The
smooth line is a filter that suppresses variations of
10 yr. length.
Source: From P. Jones, D. Conway and K. Briffa (1997, p. 2004, fig. 10.5). By permission of Routledge, London.
