Transcript Lecture 10: Impact: Extreme Weather

Impacts: Extreme Weather
Details for Today:
DATE:
BY:
14th April 2005
Mark Cresswell
FOLLOWED BY:
NOTHING
69EG3137 – Impacts & Models of Climate Change
Topics
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A Definition of Extreme Weather
Storm events
Fires
Floods and Drought
Oceans
Effects on ENSO
Societal Impacts
• Summary
A Definition
• Extreme weather may be regarded as an
anomalously high magnitude weather event
leading to deleterious effects upon natural or
human systems
• Extreme weather events are a potential
response to climate change
• These events, when they occur over land,
will often lead to damage to crops and
buildings or loss of life and economic
hardship
Storm Events
• Of all the extreme weather events – storm
events cause greatest loss of life and
damage to property
• Hurricanes – centres of intense low
pressure that feed of heat and moisture over
warm seas and land
• Tropical cyclones – primarily the result of
above normal SSTs
• Intense hailstorms and associated high
winds and rainfall
Storm Events
Storm Events
Storm Events
• Magnitude and frequency of large-scale
storms largely depends on SST anomalies
• Purely continental storm systems rely upon
intense surface heating from solar energy –
a process enhanced by deforestation and
subsequent changes to surface albedo
Fires
• During periods of prolonged drought natural
vegetation will begin to die back and dry
• Environments of this type will be highly
susceptible to either accidental or naturally
occurring fire events
• Some ecosystems rely upon fire events to
allow seeds to germinate and release
nutrients into the soil
• Climate change may enhance both the
magnitude and frequency of fire events
Fires
Floods and Drought
• Floods may be caused by excessive rainfall
or changes to the natural hydrology leading
to saturation of soils
• Apart from damage to property, crops and
loss of life, flood events may damage the
landscape – making it more vulnerable to
wind erosion
• Floods will become more common in areas
where climate change generates enhanced
precipitation
Floods and Drought
• Drought is caused both by diminished
precipitation due to climate change or
human activities
• Droughts can make environments more
vulnerable – affecting wind erosion, soil
moisture, crop/food security and human
health
• Prolonged droughts may lead to a higher
incidence of fires
Floods and Drought
Floods and Drought
Floods and Drought
Oceans
• One particular concern with climate change
is the effects on ocean surface water
temperatures
• Apart from the boundary forcing an SST has
on atmospheric characteristics, the
biological effects can be significant
• Algal blooms can form off warm water
coasts – depleting the waters of oxygen
• Changes to nutrient supply can affect fish
stocks (esp. in El Niño years)
Oceans
Effects on ENSO
• Climate simulations performed with AGCMs
using prescribed background SSTs and
ENSO-like SST anomalies indicate:
1) No change in the frequency of El Niños
2) Greater differences in precipitation and soil moisture between
El Niño and La Niña years
3) Very different patterns of change in sea-level and upper
tropospheric pressure outside the tropics in response to El
Niños – compared to the changes that occur under present
conditions
Harvey, 2000
Effects on ENSO
• Wet and dry extremes will tend to be
intensified as climate warms because:
1) Non-linearity of the Clausius-Clapeyron equation which
governs the relationship between the temperature of a liquid
and its vapor pressure
Effects on ENSO
• Wet and dry extremes will tend to be
intensified as climate warms because:
2) A given change in SST will have a larger effect on evaporation
the warmer the base climate
3) Enhanced evaporation over the eastern Pacific when an El
Niño occurs in a warmer climate will lead to a greater
increase in precipitation in this region, greater rising motion
and greater compensating subsidence in the western Pacific
4) Similar changes, but with the opposite geographical pattern
shown in (3) will occur in La Niña events
Societal Impacts
Level of agreement/consensus
From: IPCC 2001 – Impacts, adaptation and vulnerability
Established but incomplete
Well-Established
•Increased vulnerability of infrastructure to
urban flooding and landslides
•Tropical cyclones more destructive
•Fire danger to urban/rural fringe increased
•Sea-level rise increases cost/vulnerability
•Water supplies more vulnerable
•Sea-level rise increases cost/vulnerability of
coastal infrastructure
•Energy demand sensitive; parts of energy
supply vulnerable
•Local capacity critical to successful adaptation
•Infrastructure in permafrost regions vulnerable
Speculative
•Fire damage to key resources increased
•More hail and windstorm damage
Competing Explanations
•Agroindustry and fisheries vulnerable
•Heat-waves more serious for human health
•Heat island effects increase summer energy
demand and reduce winter energy demand
•Increased air and water quality problems
Amount of evidence (observations, model output and theory)
Summary
• Extreme weather events are likely to
become more serious under a warmer
climate
• Impacts on natural ecosystems with be
great – with events such as fires, floods,
drought and algal blooms
• Impacts on human society will induce
greater hardship, loss of life and economic
losses
• READ THE IPCC REPORTS!!