Impacts of Flooding and Flood Risk 1)To study the impacts of flooding 2)To understand how hydrologists try to forecast the likelihood of future floods using Magnitude-Frequency Flood Risk Analysis 1)To practice our numeracy skills by constructing a flood recurrence interval graph 13 GEOG1: Magnitude-frequency analysis of flood risk; Impact of flooding GEOG2: Logarithmic scatter graphs

Can you remember the definition for flooding?

The impact of flooding In the last century flooding has been one of the most costly disasters in terms of both property damage and human casualties. e.g. Floods in China killed nearly 4 million in 1931, and about 1 million in 1938 The 1993 Mississippi flood killed only 47 people, but the U.S. Army Corps of Engineers estimates the total economic loss at $15-20 billion

The impact of flooding  Primary hazards that occur due to direct contact with water  Secondary effects that occur because of the primary effects, such as disruption of services, health impacts such as famine and disease  Tertiary effects are long term changes such as an increase in insurance rates. According to the World Meteorological Organization (WMO), sea levels have been rising about 3 mm per year since 1993 Totaling a 200 mm increase (7.87 inches) in global averaged sea level since Flooding only looks set to increase as our climate changes, and with it will come more impacts on humans. These can be looked at at 3 times scales:

The impact of flooding  Primary hazards that occur due to direct contact with water  Secondary effects that occur because of the primary effects, such as disruption of services, health impacts such as famine and disease  Tertiary effects are long term changes such as an increase in insurance rates. Task 1)Sort the impacts out into primary, secondary and tertiary effects 2)Colour code them in three difference colours for ‘economic’, ‘social’ and ‘environmental’ (there may be more than one type on each card so you can highlight individual words etc) 3)Make notes about them

Flood Risk Risk is affected by: The frequency of flooding; how often floods can be expected. The magnitude of the flood; how severe or large each occurrence will be. The number and density of people living in the affected area. The amount of flood protection and prediction systems. The level of economic development; this affects an areas ability to afford management strategies and preparedness, and it’s ability to cope in an emergency.

Global Flood Risk in the next 30 years Figure 4: Humanitarian risk hotspots for flooding. The map shows ‘flood risk hotspots’ based on the interaction of extreme and significant flood hazard and high overall human vulnerability. Also shown are areas with significant or extreme flood hazard but lower human vulnerability and areas where climate models predict an increase in extreme precipitation, as an indicator of possible future increases of flood risk.

Flood Risk in the UK Describe the distribution of flood risk in England using your outline map.

Magnitude-Frequency Flood Risk Analysis By keeping records over many years hydrologists can predict how often a flood of a certain magnitude may occur This is called the flood recurrence interval (RI) Floods of a very large size (magnitude) don’t happen very often (they’re not very frequent) Floods of a small magnitude are more frequent Large floods usually occur due to unusually heavy or prolonged rainfall There is one exception to this rule! Large floods can still happen in places where there is annual snowmelt or monsoon rains, e.g. Bangladesh Even in areas where this does not happen it is still possible for very large floods to occur more frequently than expected.

Magnitude-Frequency Flood Risk Analysis This information can be used to decide what sort of flood protection is needed and where. A small flood may have a RI of 2 years A huge flood may have a RI of 100 years

Magnitude-Frequency Flood Risk Analysis TASK Complete the Flood Frequency worksheet for Fema Creek

Impacts in 2012 TASK Research the impact of flooding during 2012 around the world e.g. Hurricane Sandy, Egremont, Somerset and Devon, Newcastle.

Have we achieved our aims? 1)To study the impacts of flooding 2)To understand how hydrologists try to forecast the likelihood of future floods using Magnitude-Frequency Flood Risk Analysis 1)To practice our numeracy skills by constructing a flood recurrence interval graph

RECURRENCE INTERVALS In order to minimise the damage from floods it is useful to know how often a flood of a certain size might occur. The time between flood events of the same size is called the recurrence interval. This can allow planners to zone the flood plain and plan land use. They can also be used to predict the occurrence of low flow. In the UK, the Environment Agency recommends that flood defences be built to withstand a 1 in 50 year event, and builds defences to withstand a minimum 1 in 100 year event.

Work out the discharge for… years 2.5 years 3.20 years

1. Define the term flood recurrence interval. [2] 2. Explain the relationship between the flood recurrence interval and the severity of flooding [2] 3. Suggest how flood recurrence could influence land use planning and building regulations in flood plain areas. You can annotate a diagram if you wish [6] Grazing land, arable farmland, road and settlement