Environmental Engineering Reference
In-Depth Information
10 1-4 m thick, unlike turbulent flow in the nearshore zone and rivers, where it is restricted
by much shallower water depths, and air flow is not confined to narrow channels. Aeolian
bed forms can develop on a massive scale if the sediment source is sufficient.
Temperature also varies over a wider range in air than in water, which increases its
influence on air viscosity. Threshold velocities for sand particles decrease as temperature
falls and density rises, enhancing entrainment in cold climates.
STORMINESS AND GLOBAL CLIMATIC CHANGE
new developments
Climate disturbance triggers atmospheric circulatory and synoptic instability and the
public are already aware of more extreme and heavier precipitation events. Scientists now
firmly predict increases in tropical storm frequency and intensity and the reasonable
likelihood of similar increases in extratropical storms. It is instructive to compare links
between temperature change and storminess reconstructed for the later medieval period,
from AD 1300 to 1500, with forecast changes in these parameters for the twenty-first
century (Figure 1). This raises the question of how far 'the past is the key to the future'.
The rate of change is more significant than the direction (warming or cooling).
More frequent, higher wind velocities in the form of gales, hurricanes and tornadoes
will increase meteorological hazards to human life, property and economic activity. They
do not translate so easily into aeolian proceses and geomorphic 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. 353). However, global warming will promote
other changes in Earth's land surface and land-use practices. Effective wind speeds will
be enhanced, as drylands experience already with desertification (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.
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