Lecture 9: Understanding and managing flood risk 3

Question 1

Climate impacts I

Answer 1

GCMs indicate increasing frequency of wetter winters and higher intensity storms

Return periods for extreme events set to reduce in some areas (blue) but increase (floods less common) in others

May lead to increase in runoff especially in N and S Europe and elsewhere in the

Question 2

The Netherlands

Answer 2

Winter precipitation projected to increase

Low-lying and vulnerable to sea level rise (60cm+)
Floodplain of major European rivers (Meuse, Rhine)

Good flood defences but also need to adapt now

Question 3

Climate impacts II

Answer 3

Observational data for Europe shows no change in flood frequency

Despite some notable recent events

Seriousness of recent events down to increasing socio-economic exposure and media saturation

Question 4

Climate change impacts on flooding

Answer 4

Climate change and land management practices could either exacerbate or help mitigate local flooding

Most evidence is for local scale effects and for non-urban cases

Emerging mismatch between:

(a) modelled increases in future flood risk (inferred largely from precipitation - difficult for GCMs to model)

(b) trends in observed peak river flows worldwide
Huge uncertainties. Difficult to quantify. Complex.

Not just increases in total precipitation - future changes in the timing of precipitation or intensity of extremes could modify regional flood frequency behaviour.

Future changes in the inter-dependence between extreme sea surge, river flow and precipitation could affect flood risk in estuaries

Question 5

Return periods

Answer 5

Also known as recurrence interval

Estimated time period between events of a given magnitude

Statistical measurement of mean recurrence interval over long period

The higher the discharge the longer the return period

But, ‘two hundred year’ floods could occur in successive years, just very unlikely.

Question 6

Consequences of flooding

Answer 6

Fertilisation of soils

Destruction of infrastructure

Loss of life

Disruption of economic activity

Depends on exposure

Question 7

Climate extremes vs. increased vulnerability

Answer 7

Many water related issues down to increased population more than climate change

Resilience to climate change may be higher with fewer people

Infrastructure more complex and thus sensitive to increasing storminess into the future

Question 8

Mitigation: flood defence

Answer 8

Embankments, sluices, pumps, barriers. Green vs grey.

SUDS - sust. urb. drainage

Natural defences (ES, green infrastructure) cheaper than engineered ones (grey infrastructure)