Aeolian systems - Fundamentals of the Physical Environment - page 394

Storminess and global climate change

NEW DEVELOPMENTS

Climate disturbance triggers atmospheric circulatory and synoptic instability and the public are already aware of more
extreme and heavier precipitation events. The IPCC 2007 assessment firmly predicts increases in tropical storm
frequency and intensity and the probability of similar increases in extratropical storms. Increased storminess appears
to be one signature of rapid climate change and can be reconstructed for the later medieval period, from AD 1300
to 1500, and forecast for the twenty-first century ( Figure 16.6 ). The rate of climate change appears to be more
significant than its direction (warming or cooling). More frequent, higher wind velocities in the form of mid-latitude
cyclonic gales, tropical storms, hurricanes and tornadoes will increase meteorological hazards to human life, property
and economic activity. They do not translate so easily into aeolian geomorphic processes and impacts on their own,
especially in humid tropical and mid-latitude stormy belts, but it is probable that they will exploit specific environmental
susceptibilities. These occur most obviously in large expanses of sediments exposed at the coastline, which carries
the imprint of historic periods of increased storminess (see box, p. 397). However, climate change promotes other
changes in Earth's land surface and land use practices. Effective wind speeds will be enhanced, as drylands expand
and desertification increases (see Chapter 27). Intensive agricultural practices, crop yields and machinery use in humid
areas likely to experience warmer or drier climates will now come under scrutiny, on sandy/silty soils which already
experience some wind erosion.

would become dispersed as a thin amorphous layer across
the hinterland in the absence of plants and active plant
succession.
The dune landsystem is mobile until wholly stabilized
by woodland or the cessation of sand supply but various
forms and degrees of stability characterize different zones
( Plate 16.5 ). A psammosere or pioneer community arrests
sand movement along a line of embryonic fore-dunes. It
is tolerant of physiological drought, nutrient-poor and
saline-rich embryonic soils, and wind shear. Ammophila
arenaria (marram grass) and Agropyron spp. (couch grass)
are common in northern hemisphere mid-latitude fore-
dunes and have the additional ability to grow through and
anchor frequent sand burial. Progressive enlargement
and colonization establish a fore- or yellow dune barrier
which modifies the air stream and allows a more diverse
succession to develop in its lee. Shell fragments deflated
from the backshore add calcareous nutrients. The dune is
not yet stable, and parabolic blow-outs occur which
advance the dune inland by 1-20 m yr -1 . In the progres-
sively sheltered conditions of the dune slack and meadow ,
soil develops and succession advances towards shrubs
and woodland. Hind or grey dunes are more stable,
although still vulnerable to climatic change and human
disturbance ( Figure 16.7 ). Coastal dunes may individu-
ally reach over 100 m high and dune landsystems extend
for 10 1-3 km inland.

Plate 16.4 Barchanoid dunes derived from sand deflated
from a bajada and playa system, eastern Mojave desert,
south-east California.
Photo: Ken Addison