Geoscience Reference
In-Depth Information
200
African Sahel
1.0
100
0.5
0
0
-0.5
-100
-1.0
-200
SW USA
1.0
100
0.5
0
0
-0.5
-100
-1.0
-200
Southern
Africa
1.0
100
0.5
0
0
-0.5
-100
-1.0
-200
Australia
1.0
100
0.5
0
0
-0.5
-100
-1.0
-200
Patagonia
1.0
100
0.5
0
0
-0.5
-100
-1.0
-200
1900
1920
1940
1980
1990
2000
Figure 1.3
Climate variability for selected dryland areas during the twentieth century. Temperature anomalies and precipitation
departures are shown as normalised data. Dashed lines are temperature data, histograms are annual rainfall and the solid line is
the five-year rainfall running mean. The data show clearly how interannual variability is a 'normal' component of dryland climates,
and that longer runs of wetter/drier warmer/cooler conditions can also occur (data adapted from Hulme, 1996).
nature of many savanna plant communities in semi-arid
regions.
When droughts occur, plant communities that die back
to escape moisture shortages have perhaps the greatest
geomorphic significance, and changes in ground cover re-
sult. Such plants form part of what are known as nonequi-
contrast to plant communities in more temperate zones,
climax plant communities are not achieved over time be-
cause of dieback during dry periods. 'Boom and bust' cy-
cles in cover follow temporal and spatial changes in mois-
ture availability, resulting in a patchy mosaic of ground
cover. This occurs at the seasonal timescale, with, for ex-
