Environmental Engineering Reference
In-Depth Information
SURFACE MODIFICATIONS OF PRECIPITATION
So far we have considered rainfall variability over essentially flat terrain. Few areas of
the world are extensively flat, however, and surface irregularities interfere with
atmospheric processes to give even more complex spatial patterns of variation in rainfall.
Even relatively small hills can have a marked effect. The importance of surface
topography on precipitation is indicated at a general scale for the British Isles in Figure
5.12. As can be seen, the general pattern of rainfall is appreciably modified by the Welsh
and Scottish mountains. They give rise to higher totals on the western slopes, and a
marked rain shadow on the east. The effect of altitude in the leeward areas is less
apparent. For example, the Cairngorms in north-east Scotland do not stand out as areas of
higher rainfall in Figure 5.12, despite their height, because the prevailing winds have lost
much of their moisture by the time the eastern side of the country is reached.
Within any climatic region, the relation between rainfall and altitude is generally quite
consistent. In most cases,
FLOODS
applications
Floods are the most common of all environmental hazards. Each year many thousands of
people die as a result of flooding and millions are affected by indirect consequences such
as damage to crops, housing, transport, etc. Although coastal floods do occur, often the
result of tropical cyclone surges as in Florida or Bangladesh, it is on riverine flood plains
where most flood problems are found. Floods can occur in both developed and
developing countries, though the impact is often greater in the latter, where high
populations are to be found on extensive and often relatively fertile flood plains such as
those of the Ganges and the Yangtse.
Figure 1
Causes of floods.
