1 Flood Risk Management Session 3 Dr. Heiko Apel Risk Analysis Flood Risk Management

2 Learning objectives Risk Analysis Flood Risk Management  Understand: The notion of “living with risks” The Flood Risk Management Cycle  Learn: To perform a flood risk analysis How to display and analyze risks Uncertainties in risk analysis procedures To implement flood risk reduction measures

3 Flood risk Flood risk = F(Flood hazard, Flood vulnerability) Risk Analysis Flood Risk Management Vulnerability  Exposure  Value  Susceptibility Hazard  Intensity  Probability Risk

4 Living with risks  Extreme natural events are part of our environment  Risks result from interaction of hazardous processes and vulnerability  Absolute safety is not possible, however, risks can be reduced Risk Analysis Flood Risk Management

5 Flood risk management cycle Risk Appraisal Risk Analysis Risk Mitigation Residual Risk Management Risk Identification Open Risk Dialogue Open Risk Dialogue Risk Analysis Flood Risk Management

6 Risk identification - Setting the stage  Definition of flood type, elements at risk, scale and aim  Quantitative risk analysis (Kaplan & Garrick, 1981): What can go wrong? How likely is it that it will happen? If it does happen, what are the consequences?  Scenario definition  Risk: R =  S i, P i, D i , i = 1,2,…,k S i : all relevant flood scenarios P i : associated probability D i : associated damage k : number of relevant scenarios  Scenario is the basis of risk analysis Risk Analysis Flood Risk Management

7 Flood risk analysis procedure Meteorological / Hydrological simulation Statistical analysis Watershed data (DEM, land use, soils, etc.) Precipitation data Discharge data Hydraulic simulation Damage model Elements at risk Susceptability Intersection of inundation areas Dikes, Retention areas Digital elevation model River geometry Bridges, Culverts, etc. Risk Analysis Flood Risk Management

8 Displaying and analyzing the results  Risk curves Cumulated results For tangible losses  Risk maps Map typeDescription Flood danger mapShows the spatial distribution of the flood danger without information about the exceedance probability Flood hazard mapShows the spatial distribution of the flood hazard, i.e. information on flood intensity and probability of occurrence for single or several flood scenarios Flood vulnerability map Shows the spatial distribution of the flood vulnerability, i.e. information about the exposure and/or the susceptibility of flood-prone elements (population, built environment, natural environment) Flood risk mapShows the spatial distribution of the flood risk, i.e. the expected loss for single or several events with a certain exceedance probability Grünthal et al Risk Analysis Flood Risk Management

9 Displaying and analyzing the results  Risk map examples (discrete and integral): Discrete: Distribution of the damage in €/m 2 to be expected for the 1000-year flood, differentiated in land use zones. Integral: Distribution of risk zones, expressed by the integral expected annual damage Risk Analysis Flood Risk Management

10 Uncertainties – the known unknowns  Hazard, vulnerability, and risk assessments contain numerous uncertainties, esp. in extreme scenarios  Uncertainty analysis can reduce error  Through quantitative uncertainty assessment Risk Analysis Flood Risk Management Example: Risk and uncertainty analysis Lower Rhine, Germany using a 35 year annual maximum discharge series Uncertainty bounds Quantile maps

11 Flood risk appraisal What is acceptable risk? Societal risk criteria for large dams proposed by ANCOLD (1994) Risk Analysis Flood Risk Management

12 Flood risk appraisal (cont.) Determining ALARP modified after Lind et al., 1991 Risk Analysis Flood Risk Management

13 Flood risk mitigation  Technical flood defense measures Reduce discharges and water levels Protect inundation prone areas  Planning Increase of (natural) retention in the catchment (structural) Spatial planning and land use restrictions (non-structural)  Increase resilience Flood adapted construction (type, materials) to reduce damage Flood adapted building use Behavioral risk prevention – learn how to react in and cope with flood situations  Flood forecasting and Early Warning Systems Risk Analysis Flood Risk Management

14 Flood risk mitigation Early Warning Example: Bangladesh  Storm surge 1970: Inadequate Early Warning system 300,000 lives lost  Storm surge 1997: Improved Early Warning system and emergency shelters 3,000 lives lost Risk Analysis Flood Risk Management

15 Residual flood risk management  Preparedness (What happens if … ? And what to do?)  Structural/non-structural measures  Transboundary/international coordination  Crisis earth observation services, e.g. structuralnon-structural Mobile flood defenses (target specific or general) Flood forecast/Early warning Reservoir/retention basin managementEvacuation Emergency control and temporary repair of weak dikes and dams Ensured communication channels and responsibilities Risk Analysis Flood Risk Management

16 Flood risk communication  Necessary at all levels (government to citizen)  Should involve all stakeholders (planning authorities, water management, disaster management, communes)  Should utilize media (print, online, TV, radio, telephone)  Contributes to: Public acceptance of structural mitigation measures Public participation Awareness raising Individual precaution measures Effective warning systems  Increased and sustainable societal resilience to floods Risk Analysis Flood Risk Management