Geography Reference
In-Depth Information
Figure 4.1
A classification of
extreme weather and
weather-related events.
Source:
Based in part on Smith
1997.
local climate; what constitutes an unusual drought,
for example, will therefore vary with location.
Extreme events, whether relative or absolute, are
viewed as
climatic hazards
if they impose negative
stress on human activities and are considered
disasters
if they cause either considerable loss of life
or major economic losses
(ibid.)
.
Extreme weather events present several distinct
problems in their analysis. First, since by definition
many of the events are rare, sample sizes upon
which to base calculations and maps of hazard risk
are small and become progressively smaller the
more extreme the event. This reduces the statistical
significance and hence the reliability and utility
for planning purposes of hazard analysis and
hinders the detection and prediction of changes
in the extreme event magnitude-frequency with
climatic change. Second, many extreme weather
events tend to be (1) spatially localised in nature
and impact and (2) variable in size and severity,
thus complicating generalisations about their
impacts. Third, some present great problems in
forecasting either their occurrence and location
(as with tornadoes and hailstorms) or their precise
track (as with tropical cyclones). Fourth, impacts
on landscapes and societies vary not only with
event characteristics but also with numerous
human variables, such as land use, the level of
income and degree of organisation of societies and
individuals, the nature of the society, the accuracy
and timeliness of forecasting, warning and
evacuation systems, and the time since a previous
event (and hence the society's preparedness). The
design and appropriateness of hazard impact
reduction and mitigation strategies will also vary
considerably with the nature of the society.
Geographers have provided spatial and
temporal perspectives and analytical techniques in
quantifying and mapping weather hazards and in
assessing changes in risk through time, with
increasing use being made of GIS and remote-
sensing techniques. For example, in relation to
avalanches in the Alps, Gruber and Haefner (1995)
used Landsat Thematic Mapper remote-sensing
data and a digital elevation model to develop a
methodology to produce more reliable avalanche
hazard maps for planning purposes and to provide
an improved insight into the interactions of forest,
snow and avalanche risk in the Alpine landscape.
The findings of Graves and Bresnock (1985)
question the wisdom of the traditional return
period/probability approach to assessment of
extreme events, in which weather hazards are
often assumed to be randomly distributed in time
