Coastal flooding is a significant and increasing risk for some coastlines

On many populated coastlines, the risk caused by flooding far outweighs the risk caused by erosion (mainly because majority of people who live in coastal areas are only a few m above sea level)

Why People Inhabit Coastal Areas

The reasons are mainly economically based:

• Coastlines attract tourists due to access to beaches & sea ∴ meaning businesses tend to thrive here
• Deltas & estuaries are ideal locations for trade between upriver places and places along the coast
• Deltas are especially fertile & ∴ ideal for farming

Factors Causing High Flood Risk

Local

• Height → Flood risks ↑ for low lying coastal areas
  • Coastal plains, estuaries and river deltas
• Degree of subsidence → Areas that are experienced isostatic sinking
  • The Essex coast
• Vegetation removal → Ecosystems such as salt marshes and help to ↓ flood risk

Mangroves

• Mangroves ↓ flood risk in 3 ways:
  • They reduce the height of waves ∴ reducing the wave erosion of the coast
  • Their roots trap sediments ∴ raising the height of the coast
  • They reduce storm surge levels

By 0.5m every 1km of forest seawater has to pass through

• Artificial adjustments → Rivers straightening can lead to ↑ in speed w/ regards to river flow
• Topography → Some topographies result in seawater almost being funnelled (eg. Bay of Bengal)

Global

Climate warming is likely to significantly increase the risk of flooding to coasts

• Sea level rise increases the risk of flooding for low-lying coastal areas
• Increases in storm frequency and energy

Storm Surges

↳ A short-term change in sea level caused by low air pressure (particularly tropical cyclones and depressions) Most short-term coastal flooding is a result of storm surges

• Low air pressure over the sea allows the water to bulge upwards in a dome
  • Lower pressure = higher dome
• Storm surges are exacerbated by winds on top of the dome as they ↑ the height of the water at the coast ∴ increasing the risk of flooding
• When the low pressure system moves towards the coast, the dome of seawater surges ashore
• The shape of the coastline can also increase storm surges if it acts to funnel the storm surge towards an area of shallow offshore water

Climate Change

Impacts of Climate Change

• Change in Precipitation Patterns
  • Increase in the frequency and intensity of precipitation events
  • Increased frequency and intensity of storms
• River Discharge
  • Heavier & more intense rainfall = flashier hydrographs (higher discharge and shorter lag time)
  • Alteration of river regimes
• Freshwater Stores
  • Lakes ↓ in size in drier areas (subtropical dry regions have less surface water. Surface water ↑ in higher latitudes due to more runoff
  • Cryosphere Melting of large ice sheets and permafrost
• Soil and groundwater Higher evaporation rates ∴ more moisture removed from soil. ↑ in runoff in wetter areas reduces amount of runoff and ∴ infiltration & percolation = groundwater not replaced

But

• Higher temperatures
  • Atmosphere (1880-2012) → ↑ by 85C
  • Oceans top 75m (1971-2010) → ↑ by 44C
• Higher evaporation rates
  • Greatest ↑ in tundra and boreal areas in N Hemisphere
• Higher humidity

2014 IPCC AR5 report summary

Sea level	Rise between 28-98cm by 2100 Most likely 55cm
Delta flooding	Areas of world's major deltas at risk of coastal flooding likely to ↑ by 50%
Wind & waves	Some evidence of ↑ in wind speed and larger waves
Coastal erosion	Erosion will generally ↑ due to combined effects of changes to weather systems (↑ in storm events) & sea level
Tropical cyclones	Frequency likely to remain the same but intensity projected to significantly increase
Storm surges	Storm surges linked to depressions are likely to become more common

Statement: 'The impacts of climate change are difficult to tease apart from human-related drivers eg. land-use change, coastal development, pollution'

↳ Acknowledges that coasts are complex systems affected by many factors

Uncertain future

Tipping points

↳ A sudden large-scale change within a few decades, probably irreversible The IPCC in 2014 identified 7 tipping points, including:

• Long-term droughts
• Collapse of monsoon climate system
• Arctic Ocean becoming ice free

Human factors causing uncertainty

Economic growth

More developing countries have emerged economically in last 30 yrs ∴ use of energy & higher emissions (China)

↳ Still many countries to develop so global emissions may continue to increase

Population

More people, w/ higher levels of wealth use more energy & ∴ cause more emissions BUT education makes people more aware of issues (Kuznets curve)

Energy Sources

Global agreements (eg. Paris, 2016) on emissions reductions make countries review their energy mixes

↳ ∴ renewable technologies are being developed & used more, but fossil fuel resources are still being exploited

Adaptation Strategies

Strategy	Positives	Negatives
Water conservation & management	Low-cost appropriate tech possibilities exist	• Only works when everyone participates • In extreme areas, expensive large-scale schemes may be required which are hard to get internal agreement for and can result in tensions & conflict
Resilient agricultural systems	• Changing farming cycles/crops to match a new climate may secure food production	• The process takes time and may not be effective if climate change is severe • Diversification only works if targeted & backed by policy makers, markets & farms
Land-use planning	• Keeps vulnerable human activity away from risky areas (eg. coasts or floodplains) • Building changes can allow structures to resist changes eg. more intense storms	• Require strong local admin, enforcement & wealth (not always possible in developing nations) • Hard to move existing land-uses in risky areas due to land ownership & level of compensation required
Flood risk management	• Identifies areas w/ increased flood risks & adapting the structures within them • Rivers and floodplains can be managed w/ afforestation & wetlands to control river discharges/mangroves at coasts to impede storm surges	• Costs may be too high • Requires a lot of people to move (especially afforestation) • Local people may object to moving • Prediction of actual flood levels in uncertain ∴ adaptation methods may be ineffective
Solar radiation management	• Involves reducing amount of heat energy reaching the Earth's surface	• Most geo-engineering is expensive, requires unproven tech & needs international agreement

Mitigation Strategies

Strategy	Positives/what is it	Negatives
Renewable switching	• Would greatly reduce carbon emissions	• Such technology not always available in developing countries
Carbon capture & storage	• Power stations and large factories that use fossil fuels can be made to capture & store emissions by laws	• Suitable geologic sites may not be available • Technologies involved may be too expensive • Reduces profits of the companies & economic priorities may be out first
Energy efficiency	• All types of machinery/appliances have become more energy efficient (mainly due to gov regs) • People have the ability to change their lifestyles to use less energy	• As avg global wealth increases, more energy used
Carbon taxation	• Govs can encourage businesses and industries to change to low-carbon alternatives by imposing taxes on carbon emissions	• Alternatives & new technologies are expensive • Businesses and people may be slow to adopt these mitigation strategies/willing to accept extra tax cost
Afforestation	• Planting more forests increases storage and reduces atmospheric concentrations of carbon	• Many countries are deforesting for commercial/subsistence purposes • Difficult to get international agreement as forest resources are economically important