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Severe weather and flood events (UK severe weather (Heat waves, Fog,…
Severe weather and flood events
UK severe weather
Heat waves
Fog
Rainfall
Wind
Snow/ ice
Poor air quality
Types of flooding
Fluvial (river)
Excessive rainfall causes a river to exceed capacity
Water rises over river banks onto flood plains
Pluvial (surface)
Run-off from hill slides unable to absorb water
Floods before the water enters a watercourse/ sewer
Coastal
Sea water floods coastal land areas
Storm surge=
extreme tidal condition, high winds push water onshore
Flood risk defined by 1 in 100 year event (1% chance of flooding in a given year)
Weather
Weather fronts mark the boundary between two air masses (warm/ cold, moist/dry)
Most of UK rainfall due to frontal weather systems
Isobars=
Lines of constant mean sea level pressure (hPa)- close together means strong winds
Cumulonimbus clouds are a sign of convective weather- common in summer
Jet streams
Strong upper air current that circumnavigates the globe
Strong winds guide the track of low pressure systems across Europe
Wet weather during Storm Desmond and storm Eva (sept 2015-Dec 2015) influenced by jet stream- directly over the UK in Dec 2015
Possile that cold sea surface temps in N.Atlantic associated w/ El Nino influenced position of jet stream- not known
Found 9-16km above the surface and reach v high speeds
El Niño
Warm phase of ENSO- measured through Southern Oscillation Index
Conditions
Sea surface temps in East become warmer
Atm pressure falls and convection increases in East
Atm pressure rises and convection decreases in the West
Band of warm ocean water in equatorial Pacific
Difference in pressure between Darwin, Australia and Hawaii
Rainfall & Climate change
Theories: precipitaiton intensity will increase -> more flooding
Extra moisture provides more energy to the storm- intensifying it & allowing it to draw even more moisture
More moisture evaporated from surface
Air is able to hold 7-8% more moisture per 1 degree C increase
Global mean temps are increasing
Atmospheric rivers projected to increase in frequency
Atmospheric rivers=
regions in atm in which water vapour is transported in v high concs
Coastal flooding- storm surges
1953 storm surge
Tide was 5.6m above annual average
32,00 people evacuated
2126 people died
from England, Scotland & Netherlands
Storm surge protection
Thames barrier: operational since 1982 to protect against 1 in 100 flood till 2030
Expected to be used 2-3x/ year -> being used 6-7/ year
Better flood defences, weather forecasts, tidal forecasts, energy plans
Highest impact during:
Intense storms- v low surface pressure
High tides
Strong winds
Spring tides (just after new or full moon)- greatest difference between high and low water
Severe weather/ flood warnings
Environmental Agency:
detailed flood forecasts and action taken
Flood Forecasting centre:
flood forecasts
Met office:
forecasts and weather warnings
Risk matrix-
likelihood of severe weather vs potential impact
UK storms (2015)
Storm Eva
Rain a month before caused ground to be saturated
Mean rainfall in Lancashire for Dec- 100mm
Stationary fronts over N. England- transported warm moist air from South
Storm Desmond
Carlise flooded completely
Pooley Bridge and A591 road collapsed
Flood defences built in Keswick 1009- £6 million to protect from 1 in 100 year event