Hazards Concepts - University of Colorado Boulder · PDF fileenvironmental systems. ......
Transcript of Hazards Concepts - University of Colorado Boulder · PDF fileenvironmental systems. ......
1
Hazards Concepts:
Explanatory Paradigm
• Behavioral: choices made by individuals and governments.
– Aka: Decision-making or choice paradigm
– (mis) Perception
– Technical solutions
• Development: the political-economic context, especially:– LDC vs. MDCs
– Often a critique of, colonization and development models.
– Reform of development and development institutions (e.g., World Bank) as solution
Hazards Concepts
• Natural Hazards: the interaction of human exposure and vulnerability and natural extremes
that creates loss and disruption in social and
environmental systems. (We include Smith’s “super
hazards” like asteroids, in this category).
• Disasters: hazard events causing large loss of life and severe property / economic loss. (Chap. 2)
We’ll deal mostly with natural disasters. [Smith and
Petley: actualization of a hazard].
• Risk: a measure of likelihood of an event and its
consequence (Chap. 4)
Hazards Concepts
• Exposure: physical and geographical coincidence of human occupancy and
investment and spatial extent of natural
extremes.
– Population and Property “at risk”
– Hazard zone occupance
• Vulnerability: tendency of place, group, or society to incur losses to hazards (“given
hazard”).
Hazards Concepts
• Factors in Vulnerability (pp. 15-20)tendency of place, group, or society to incur
losses to hazards.
– Economic: poverty = vulnerability (lacking of
capital, land, tools, options, information) Also:
higher proportionate loss
– Social: Age, gender, disability, health
– Political: bad government, war, political minority
– Environmental: unsustainable resources and
degraded environments
Hazards ConceptsTogether, trends in Exposure and Vulnerability must yield loss trends. BUT: how defined and measured?
– Simple total loss or loss trend?
– Distribution of loss across society?
– Proportionate loss of population or property at risk?
Impact / Loss trends:• Total (gross)---but should be de-trended for inflation (=constant dollars)
• Uncompensated or mitigated (net; also insured and un-insured)
• Benefit/Cost accounting (net)
• Marginal Benefit/Cost (additional value minus additional loss)
• Per unit of exposure (= vulnerability) Re-analyzed versions of this NOAA flood damage data set, similar to graph in the
textbook. Here is deflated (or constant) dollar losses.
BUT---how should we “normalize” to measure loss
per unit of exposure? First, constant dollars (1995):
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THEN: ratio of some logical measure of exposure:
e.g., per population:
Or unit of wealth, development (buildings, homes),
investment, etc.:
Hazards Concepts
Resilience: the capacity to absorb and recover from a hazard event: rate of recovery
– Individual
–Collective
– Varies with wealth, preparedness, and other factors
Reliability: frequency with which systems (including hazard protection systems) fail (or don’t fail!)
Hazard Concepts
• Smith, Ch. 1
• Burton, Kates, and White, Ch. 2, pp. 19-31
Smith and Petley offer a bit
of a challenging illustration,
in which natural vs. man-
made (I would say
“technological”) and
voluntary vs. involuntary
make sense, but intense vs.
diffuse makes less sense (at
least to me).
As discussed in class,
certainly the middle natural
hazards like flood, drought,
and wildfire can have their
basic processes altered by
human action (as opposed
say to (EQ and volcano) like
land development, forest
management, and the
spread of irrigated
agriculture.
3
Societies range from
those that are
“secure” (e.g., high
absorptive capacity
and lots of
adjustments
available) to those
less so (poorer
societies with fewer
options), and these
can be in risky places
(Bangladesh, New
Orleans) or in relative
safe places (Colorado
or Dubai).
Ian Burton, Gilbert White, and Robert Kates
The Environment as Hazard (Oxford UP) pp. 19-31:
Defining and Measuring
Hazards
We’ll focus on Geophysical events
as hazards.
Measuring Hazards• Magnitude (or intensity): speed of wind, height of flood,
depth of snow, ground motions of earthquake.
• Frequency:
– Simple frequency: how often event occurs in given time frame,
– probability: chance in % or fraction of one of occurrence in some time frame (coming in Ch. 4)
– return period: average time between occurrences (of given magnitude). (coming in Ch. 4)
• Temporal spacing random vs. cyclical, clumpy, etc.
• Duration
• Areal extent
• Speed of onset
• Spatial dispersion
Intensity or magnitude
is measured and expressed in various ways (wind speed, central pressure,
ground movement as % of g---the acceleration of gravity, etc.).
But some analysts create simpler, categorical measures or scales, so they
create simple scales like the Safir-Simpson hurricane scale, Fujita tornado
intensity scale, Mercalli earthquake scale, and volcano explosivity index. In my
view, intelligent people can deal with more direct measures, and these scales
lack specificity, and some, the Snowstorm scale (below), just seem a bit silly.
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Sample Scales of Hazard Intensity
We’ll take these and other measures up in
detail in the hazard-specific lectures and
chapters----here we use these as
examples to introduce the various ways
we measure intensity.
The Mercalli scale was developed to categorize the surface effects of an
earthquake as experienced by people and buildings, all affected by magnitude of
waves, type of surface, and type of human use.
“Drivers of autos disturbed”
“Waves seen on ground, line
of sight distorted”
“Many frightened and run
outdoors”
“Everyone runs outdoors”
10% chance in 50 years
Here’s example ground motion risk map---we go over steps in
EQ risk assessment in EQ lectures.
Ground motions for known magnitudes and relationship b/w ML and shaking
can be established, and then linked to frequency of seismic activity. Here are
peak velocity contours for the magnitude 6.7 1994 Northridge earthquake.
Contours of velocity are in cm/sec, measured by accelerometers. Red star is
epicenter, note peak motions off-set to north along foothills.
Another step in risk assessment is to map actual damage, here expressed
by the Modified Mercalli eq intensity scale, and link it to ground shaking, and
thus be able to project damage into the future.
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Frequency is measured and analyzed in other ways. A typical starting
point is a histogram of events that plots frequency (number of
occurrences) against magnitude, with magnitude arrayed into classes
(aka “class intervals” or “bins”---in Excel).
Here is histogram of annual average temps for Boulder, 1948-2005.
Ann vbg Temp 1948-2005
024681012141618
46 47 48 49 50 51 52 53 54 55 56 57 58
More
Avg. Temp
Freq
You will create a histogram of
snowfalls in exercise 1, so be
sure you know what they how
and how to construct one.
This is straightforward
descriptive statistics, can be
done in Excel, and you can
count on the voracity of
Wikipedia entry on it.
Same data with different
intervals.
Mean (average) often is most frequent (mode), but not
always!
We’ll also use: Probability and Return Period to define
frequency, but won’t get to those until in Chap. 4.
The previous graph was a histogram of intensity plotted against frequency, this is
a time series of intensity (snow depth) over a period of years. Note it is plotted as
% of average (so 100% = mean; this method, also called “departure from normal”
or average, is often used for meteorological variables). A time series reveals the
temporal pattern & trend—in this case seemingly random over time (e.g., not
clumped with no obvious trend).
Mean
The times series
of rainfall in
Switzerland
(top) appears
relatively
random over
time, but the
rainfall in the
Sub-Saharan
Africa (the
“Sahel”--
bottom) does
show strong
clumping of
extremes over
time, especially
in the second
half of the
record.
Measuring Hazards• Magnitude (or intensity): speed of wind, height of flood,
depth of snow, ground motions of earthquake.
• Frequency:
– Simple frequency: how often event occurs in given time frame,
– probability: chance in % or fraction of one of occurrence in some time frame
– return period: average time between occurrences (of given magnitude).
• Temporal spacing random vs. cyclical, clumpy, etc.
• Duration
• Areal extent
• Speed of onset
• Spatial dispersion
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Comparative
Measures:
Characteristic profiles
for hazards can
illustrate differences in
monitoring (e.g.,
immediate for
earthquakes, long-term
for droughts) and
warning systems.
Smith and Petley offer a bit
of a challenging illustration,
in which natural vs. man-
made (I would say
“technological”) and
voluntary vs. involuntary
make sense, but intense vs.
diffuse makes less sense (at
least to me).
Certainly the middle natural
hazards like flood, drought,
and wildfire can have their
basic processes altered by
human action (as opposed
say to (EQ and volcano) like
land development, forest
management, and the
spread of irrigated
agriculture.
Societies range from
those that are
“secure” (e.g., high
absorptive capacity
and lots of
adjustments
available) to those
less so (poorer
societies with fewer
options), and these
can be in risky places
(Bangladesh, New
Orleans) or in relative
safe places (Colorado
or Dubai).