Workshop of Working Group F on Floods Vienna.04.06 Flood Risk Assessment in a Changing Environment H.P. Nachtnebel Dept. of Water-Atmosphere-Environment Univ. of Natural Resources and Applied Life Sciences hans_peter.nachtnebel@boku.ac.at
Objectives Discussion of a framework to assess flood risk in a changing environment Role and importance of uncertainties inherent to the assessment process Strategies to avoid (reduce) emerging risks
Layout of the presentation Some definitions and terms What do we observe with respect to flood risk? What are the changes and what are the reasons? What can we conclude? What kind of options do we have?
Speaking about flood risk Risk assessment and management is discussed by using a variety of terms, such as risk hazard exposure susceptibility vulnerability coping capacity resistance resilience adaptive capacity
Definition of risk flood risk combines the probability of a flood event and of the potential adverse consequences for human health, the environment, cultural heritage and economic activity (Directive 00/60/EC). Is frequently expressed as the expected annual damage (Merz et al. 00) R( X * ) X * f ( Q) D( Q) dq Q X i * f ( Q ) D( Q ) i i f(q) flood frequency D(Q) damage (losses) X* resistance
Flood risk management The main objectives are: Reduce efficiently economic losses ( ): properties, infrastructure, production, transportation.. minimize casualties and social impacts Protect cultural heritage Minimize ecological losses
What is the basis of risk assessment? Observations of flood series to estimate f(q) observations of flood damages to estmate D(Q) Annual mamixa at gauging station Korneuburg/Reichsbrücke (BMLFUW, 04) Annual major flood losses in Europe (Barredo, 009) today future
Observations: Flood damages are the most frequent and costly natural hazard (Jongman et al., 0; UNISDR, 0). the respective economic damages are about $9 billion/a (Kundzewicz, 00) and more than 5 million people/a are affected globally have increased in most regions of the world during the last decades (de Moel et al., 009, Barredo, 009; Bouwer et al., 00; Kreft, 0; UNISDR, 0). This fact is surprising because many countries, especially in Europe, have annually invested substantial amounts in physical flood protection measures, such as levees, dykes and flood detention reservoirs.
Observations: flood damages are the most frequent and costly natural hazard (Jongman et al., 0; UNISDR, 0). the respective economic damages are about $9 billion/a (Kundzewicz, 00) and more than 5 million people/a are affected globally have increased in most regions of the world during the last decades (de Moel et al., 009, Barredo, 009; Bouwer et al., 00; Kreft, 0; UNISDR, 0). This fact is surprising because many countries, especially in Europe, have annually invested substantial amounts in physical flood protection measures, such as levees, dykes and flood detention reservoirs. (Munich Re, 03)
Changes in flood frequency? (estimation of a HQ 00 by a moving window Gauging station Stein/Krems Danube) Peak discharge (m 3 /s) Moving window 50 years Peak
Changes in flood frequency Elbe river at Decin Time Series of winter and summer floods at Decin (Elbe) (Yiou, P. et al, 00) Water Resources Planning and Decision making Unit H.P. Nachtnebel
96 96 963 964 965 966 967 968 969 970 97 97 973 974 975 976 977 978 979 980 98 98 983 984 985 986 987 988 989 990 99 99 993 994 995 996 997 998 999 000 00 Tage Do heavy rainfall events become more frequent? 6 5 Zahl der Tage mit mehr als 30 mm Niederschlag in Wien Reihe 96-00 Number of days per year with more than 30 mm/day (Vienna) 5 4 4 YES!!!! 4 4 3 3 3 3 0 0 0 0 0 0 0 0 0 0 0 0 Jahr (after Rudel, ZAMG 00)
903 905 907 909 9 93 95 97 99 9 93 95 97 99 93 933 935 937 939 94 943 945 947 949 95 953 955 957 959 96 963 965 967 969 97 973 975 977 979 98 983 985 987 989 99 993 995 997 999 00 Tage Do heavy rainfall events become more frequent? Zahl der Tage mit mehr als 30 mm Niederschlag in Wien Reihe 903-00 6 5 5 Number of days per year with more than 30 mm/day (Vienna) 5 5 5 4 3 3 3 3 3 44 33 4 4 3 3 4 3 NO 44!!!! 3 4 3 3 4 3 4 00 0 0 0 00 0 0 0 0 0 0 0 00 0 0 0 0 0 Jahr (after Rudel, ZAMG 00)
Future changes in flood frequency The IPCC report on extreme events (IPCC, 0): there is limited to medium evidence available to assess climate driven observed changes in the magnitude and frequency of floods at regional scales. low confidence at the global scale regarding even the sign of the changes. The AR5 (Hartmann et al., 03) report: there is currently no clear and widespread evidence for observed changes in flooding except for the earlier spring flow in snow-dominated regions, at least in Europe and Asia. Arnell & Gosling (04): Under one climate model (HadCM3 and SRES Ab) in 050 the current 00-year flood would occur at least twice as frequently across 40 % of the globe
Future trends? Lack of evidence and thus low confidence regarding the sign of trend in the magnitude and/or frequency of floods on a global scale over the instrumental record. With high confidence, floods larger than recorded since the 0th century occurred during the past five centuries in northern and central Europe, the western Mediterranean region and eastern Asia. (5 th IPCC Assessment report)
What do we conclude? The reported flood damages show an increasing trend The reports about changes in flood frequency exhibit a large uncertainty and even opposite trends were found Consequences for risk assessment: Although we see (expect) trends, variabilities in the time series we estimate future risk from past observations Risk becomes time dependent
Redefinition of Risk Risk: R( X *, t) * X f ( Q, t) D( Q, t) dq f(q,t) flood frequency D(Q,t) damage (losses) X* resistance But then we have to trade-off future risk with todays risk (we have to discount the future)
What might be the reasons? Analysis of hydrological changes due to direct human impacts local measures (river channelisation) Regional measures (hydropower and flood protection) Large scale impacts (reservoirs and irrigation)
Local scale: Channelisation of rivers Frequently flooded
Impacts on floods Partial duration series of flood peaks Partial duration series of floods (96-99) River training works
Impacts on floods Partial duration series of flood peaks Partial duration series of floods (96-99) River training works
Climate change? No significant changes in the annual precipitation (rather a decrease) No significant change in intensive rainfall events Partial duration series of intensive rainfall events (Sajach) Intensive rainfall events in the catchment
Large scale: Upper Danube Basin hydropower schemes, levees and dams (Section of about 350 km)
Danube river: travel time of floods (From Miklanek et al., 000) (Miklanek et al. 003)
Analysing trends in flood losses Pielke & Downton (000): USA Barredo (009): Annual flood losses in Europe Original losses (US $) normalized data (inflation, population change, purchasing power)
Analysing flood damages The observed growth of flood damages is dominated by societal changes as changes in population density, and economic development (Hoppe & Pielke, 006; Mitchell, 003; Merz et al. 00) About 43 % of increase in flood damage can be attributed to population growth (Pielke and Downton, 000) No standardised approach for flood damage assessment Large uncertainties in flood damage assessment (Thieken et al., 008)
How to identify and assess emerging risks? Directive 007/60/EC requires repeated preparation of flood risk maps recognising the dynamic aspects in flood risk But still, mostly we look back when taking decisions for the future Whats about using scenarios? Assess recent damage potential for different flood events Assess trends in population density Assess future damage potential according to regional development plans for the same flood events Assess the sensitivity of the damage potential with respect to magnitude of the flood
Application to a province in Austria: Recent damage potential Recent damage potential obtained by overlay of cadastrial maps with inundation maps (HQ 30, HQ 00, HQ 00 sometimes HQ 300 ) Estimation of inundated residential areas and normalisation (% of building area) (Neuhold et al., 0) HQ 30 HQ 00 HQ 300
Recent qualitative flood risk
Emerging flood risk Analyse demographic changes Analyse regional development plans already designated but not utilized sensible land uses in the flood plain how strongly are development plans in conflict with (existing and future) inundation areas Estimate emerging damage potential
Demographic changes until 030
Changes in the damage potential Recent and emerging risks can be identified
Combining recent risk with emerging risk Hot spots: Area exhibiting already today high risk that will additionally increase in the future
Climate change driven flood risk Assess recent damage potential Consider regional development plans and demographic changes Sensitivity of changes of inundated (residential) areas with respect to DQ cc in HQ 30, HQ 00, HQ 300 (+ 0% in HQ 300 ) Identification of areas sensitive to climate change and regional development (sensitivity analysis by increasing flood peak by 0 %)
Conclusions: At the local scale land use changes may have impact on floods The climate signal in flood frequency may be regionally different and exhibits large uncertainties Increase in flood damages is correlated with economic development, migration etc. Increase in flood damages is mostly due to conflicting land uses with inundation maps Land development plans exibit often a stronger impact on the damage potential than changes due to climate A concept was presented which utilises available information layers to identify emerging risks with respect to land use changes and climate change Based on this information hots spots and a risk management strategy can be identified Tje approach is considered as robust as it tries to reduce regional land use conflicts reducing the vulnerability
Thank you for your attention hans_peter.nachtnebel@boku.ac.at