Dottorato Internazionale Congiunto / Europ . Graduiertenkolleg

1. UNIVERSITÀ DI FIRENZETUC.-W. ZU BRAUNSCHWEIG Dottorato Internazionale Congiunto  /Europ. Graduiertenkolleg IS EOLIAN RISK AS SIGNIFICANT AS OTHER ENVIRONMENTAL RISKS? G. Augusti, C. Borri & G. Bartoli CRIACIV Firenze/Prato, March 2nd, 2002

2. INTRODUCTION -1- • One estimates 15 Mio casualties in the last 1,000 year in at least 100,000 natural catastrophes (droughts & famines excluded) • Steep increase in number of natural catastrophes and in the induced losses (due to higher concentration of people and values) • Gradually declining number of casualties (due to improved early warning systems and protection techniques) • Economic losses due to natural hazards (1) • Earthquakes: 35% Floods: 30% Windstorms: 28% • Insurer’s total claim burden from natural catastrophes (1) • Windstorms: 70% Earthquakes: 18% Floods: 6% Others: 6% • Main causes in term of fatalities: • Earthquakes: 47% Windstorms: 45% Floods 7% (1) Figures according Munich-Re, GeoRisk Research Group (1998-2001); G. Berz & E. Rauch, WTG 1998 & 2001, Braunschweig

3. INTRODUCTION -2- • Windstorm catastrophes have, in recent year, produced enormous human and economic losses and hit financial operators particularly hard: in December 1999 two storms, Lothar and Martin, causes the loss of over 100 human lives with approximately 14 billion € overall loss estimated • Which are the main causes of such dramatic increase of losses? • Migration of population into wind-hazardous areas • Changes in environmental conditions (increase of OCCURRENCE) • Gradually declining number of casualties (improved early warning systems and protection techniques) 2 Berz G., Rauch E. (1998) WTG Colloquium, Braunschweig

4. INTRODUCTION -3- • Too many “informal housings” are still in use, whose VULNERABILITY is too high • Modern, lightweight buildings & structures are also becoming more VULNERABLE • Correct identification of wind loads in Design Rules is still not yet completed in many “critical” situationspre-normative research • Lack of more stringent countermeasures, like: radical land use restrictions, prevention of secondary losses, improved windstorm forecast and emergency plans, reduction of greenhouse-gas release, lack of finalised research (both in quantity and in quality)

5. WHAT’S EOLIAN RISK? - 1- • Risk (= presence of danger) as a counterpart of Safety ( = absence of danger) • No “yes-or-no” definitions can be applied in actual conditions; never to engineering facilities • Possibility of unwanted events (& consequent losses) cannot be excluded altogetherSafety shall therefore be referred to as acceptable risk or reliability • In probabilistic terms, the Eolian Risk associated with physical damage to build facilities (damage risk) is given, in analogy with the terminology most commonly accepted in civil engineering, by R = Poc · Pex · Pda

6. WHAT’S EOLIAN RISK?-2- R = Poc · Pex · Pda where • Poc is the “Wind hazard” (i.e., the probability of occurrence of a dangerous event, “the action”) • Pex is the “Eolian exposure” (i.e., the probability that the action finds something that can be damaged) • Pda is the “Eolian vulnerability” (i.e., the conditional probability that the facility is damaged when hit by the action) Poc , Pex and Pda are often no yes-or-no quantitiesrefined definition of the 3 quantitiesthe product becomes a “convolution integral” of quantitatively-defined vulnerability, exposition & site hazard

7. WHAT’S EOLIAN RISK? -3- R = Poc · Pex · Pda • Site hazard (sometimes improperly indicated as risk): is the probability of occurrence of the dangerous event in the relevant site intensity - Poc curves (for given time spans) • Exposition (exposure): is related to the presence of vulnerable facilities in the site: • population & wealth tend to increase in wind prone areas • increase of “exposition” is thought to be the main cause of increase of wind damages in recent decades  • Vulnerability: is the sensitivity of the facility to the damage (rigorously: the ensemble of conditional (*) probabilities of attaining or exceeding each “degree of damage”) • preventive “measure” of the degree of damage (from no. damage to complete failure) (*) upon the occurence of the event of each given intensity

8. WHAT’S EOLIAN RISK? -4- • Reliability: is the complement of risk (1 - risk), sometimes unproperly used to indicate the complement of vulnerability • Each Damage is associated to its consequences Losses • economic losses (measurable in monetary terms), direct or indirect (long term) economic risk • losses of life and limb (casualties)  referred to as “intangibles” casualty risk • Losses as measure of damage itself   exp. cost of damage = cost of damage  probability of damage (i.e. risk) (convolution integral)

9. THE EOLIAN HAZARD -1- 3 • 3 categories of wind storms, in ascending damage potential: • 45 m/s synoptic storms (or winter storms) of mid latitudes • –lasting several hours • 70 m/stropical cyclones (like hurricanes of typhoons) • – lasting a few hours • 120 m/stornadoes (thunderstorms) • – lasting a few seconds at each site • Occurrence: some recent data & new findings on the Eolian hazard and induced damage are available in Europe after December 1999 series of storms: Anatol, Lothar, Martin 3rd, 26th & 27th December 1999

10. THE EOLIAN HAZARD -2- 4-5 WINTER STORMS 1999: BEAUFORT –12 (HURRICANE) Anatol: 3.12.1999 • Mainly hit regions: Denmark, Germany, UK, Sweden, Lithuania, Lettland, Russia, Poland • Casualties: > 20 • Socio-economic losses: 2,5 Bill. € (estimated) • insured single damages: 600,000 € • Main damages: roofs, façades, vehicles, boats, temporary structures (like scaffolding) • Infrastructures: 165,000 houses without power supply (major damages occurred to overhead lines in Denmark & Sweden)

11. THE EOLIAN HAZARD -3- 6-8 WINTER STORM 1999: BEAUFORT –12 (HURRICANE) Lothar: 26.12.1999 • Mainly hit regions: France, Germany, Switzerland, Belgium, Austria, Italy • Casualties: 110 • Socio-economic losses: 11,0 Bill. € (estimated) • Insured single damages: 2,4 Bill. € • Main damages: roofs, temporary structures, cranes, overhead lines, forests, • Infrastructures : 4 Mio families without power supply for several weeks(South-West France); EDF reported (non-insured) losses of some billions € (supply lines & power plants) public transport interrupted for some days (Paris area); closed airports; telecomm. networks highly disturbed for several days

12. THE EOLIAN HAZARD -4- 9-10 WINTER STORM 1999: BEAUFORT –12 (HURRICANE) MARTIN: 27.12.1999 • Mainly hit countries: France, Spain, Italy, Switzerland • Casualties: > 30 • Socio-econimic losses: 4,0 bill. € (estimated) • Insured single damages: 1,0 bill. € • Main damages: see Lothar • Other damages: Historical Buildings (castles, abbeys)

13. THE EOLIAN HAZARD -5- 11 WINTER STORM 1999: BEAUFORT –12 (HURRICANE) • COMPARISON with the storm-series 1990: • Insured losses in 1990-storms (re-valued) / insured lossed in 1999-storms = 1.5 • In Denmark and France new extreme values (records) were reached as cumulative damage in a single storm: • Denmark: Anatol’s (1999) damage / Daria’s (1990) damage:  20 • France: Lothar’s (1999) damage / Herta’s (1990) damage:  4 • Germany: Lothar’s (1999) damage / Vivian’s (1999) damage:  2/3 (concentrated in South West)

14. THE EOLIAN HAZARD -6- • EFFECTS OF CLIMATE CHANGES • Warming up of the atmosphere is going on after the 1st world war (main sources are man made) • Change in time of mean temperature clearly shows a new trend with a dominating virulent effect in the Northern Hemisphere:  • +0.7 °K in last 80 years • -0.2°K in last 1000 years • More probable is an aggravation of the wind conditions with regard to storm intensity and frequency in Europe. Some recent findings (1) definitely show: • warming up of the atmosphere  warming up of ocean  raise of sea level and water vapour content of atmosphere  more energy for building up intensive low pressures vortices over tropic & extra-tropical oceans + more vehement thunderstorms overland. (1)Berz G., Rauch E. (1998) WTG Colloquium, Braunschweig

15. THE EOLIAN HAZARD -7- • EFFECTS OF CLIMATE CHANGES • the number of strong low-pressure system over north Atlantic and Europe has risen by  40% since the 30’s, No. Of extreme events even more – As an example, lowest central pressure ever observed in the area (920 hPa) was recorded in recent years. • the usual cold winter high pressure system that builds up in central/eastern Europe (over snow surfaces) was much weaker in the last 10 years (unusually mild with little snow)  The “Barrier Effect” to Atlantic low pressure system was less pronounced Atlantic low pressure were able to penetrate much further into central and eastern Europe • by continuos raise of winter temperatures in Europe, windstorm clusters like Jan.-Febr. 1990, Jan. 1993 & Dec. 1999 may gradually become the norm

16. THE EOLIAN HAZARD -8- 12-13 • EFFECTS OF CLIMATE CHANGES • As an example : base on wind data from the Düsseldorf area(1), the No. of large storms (mean wind speed >17.2 m/s, Beaufort 8) increased as follows : • 105 events in 5 years (at beginning of 60’s) • 182 events in 5 years (1990-94) • storm intensity : the trend is less evident, but the probability of extreme events increases as the total No. of events grows (1) Kasperski, M. (1998), Wind & Structures, 1, no. 2

17. THE EOLIAN HAZARD -9- • EFFECTS OF CLIMATE CHANGES • FUTURE SCENARIO • Should design wind speed “depend on year of construction”, extrapolating the observed trend in the storm frequency in the future? • The basic design wind speed of Eurocode 1 is set (in absence of any trends) at 24 m/s : due to the observed trend, the analogous value for the year 2028 would rise to 29 m/s  46% increase of the design load (as this is proportional to the square of the velocity)??? • Alarming result: does this imply that wind storm occurrence may not be longer considered as a stationary process? • If yes  shall design wind speed become depended on the year of construction (taking into account the expected life)?

18. THE EOLIAN HAZARD -10- 14 • EFFECTS OF CLIMATE CHANGES • Storm scenarios with cumulative damage return period of 100 years

19. EOLIAN VULNERABILITY OF ENGRG. FACILITIES -1- 15-19 • Vulnerability to wind storms of built-up environment is drastically increasing • There are several different aspects of “vulnerability” all of them contributing to the increase of “eolian risk” : • “non-engineered” buildings (concentration of people in poor buildings, often built without any construction rule) • the challenges of the modern engineering facility, i.e. carrying ext. loads while ensuring a certain level of safety, minimising the material employed, and optimising the constr. process & time; main facilities concerned are: • large structures • tall buildings • long-span bridges • wide-span enclosures & roofs • light-weight structures (with high-resistance material) • telecommunication facilities, like masts & towers • life-lines (overhead electricity lines, power plants)

20. EOLIAN VULNERABILITY OF ENGRG. FACILITIES -2- 20-24 • Temporary structures and secondary elements (often neither planned nor designed to withstand wind loads); major sources of economic losses have been identified by : • large cladding facades (glass wall) • road – signs • urban fittings, also referred as street-architectures (lamps, placards, free standing objects) • scaffoldings, temporary stands, • sun screens, noise barriers

21. EOLIAN VULNERABILITY OF ENGRG. FACILITIES -3- • Countermeasures for mitigating eolian vulnerability: • suitable estimate of Design Wind Speed, taken as the basis of calculation (10-min-average velocity, with 2% yearly probability of exceedence, i.e. roughly the 50-year return period); surface roughness • accurate prediction/simulation of wind pressure field design loads  wind tunnel experimental tests • stricter compliance with some elementary construction rules & execution details • more attention to smaller but more frequently occurring wind intensities: preventing “fatigue” risk • recommended: introduction of several intensities of “design storms”, to define the total eolian hazard(1), in analogy to earthquake engineering (two levels: for ultimate limit state and for serviceability limit state, respectiv.) (1)EUROCODE 1 allows, in principle, this concept, by introducing the probability of exceedence as function of the wind velocity

22. OTHER TYPES OF (EOLIAN) RISK -1- • Atmospheric wind may be the source of several other kinds of risk, related to “quality of life”, hardly to evaluate and to be quantified, and each related to “vulnerability, exposure & hazard”, like: • discomfort risk • pollution risk dissatisfaction risk (long lasting effects) • …………… • wind, even of moderate intensity, can be a source of great discomfort to every day life (f.e., it influences the dispersion of gas and pollutants) • dissatisfaction risk may be sometimes very negative: urban wind climate of badly designed areas (plaza, streets, free surfaces around buildings does highly affect the socio-economic aspect of life • need of introducing appropriate definitions for “vulnerability, exposure and hazard” for each dissatisfaction risk, and consequently, for the whole wind climate (not only for strong winds)

23. OTHER TYPES OF (EOLIAN) RISK -2- • wind design” should not exclusively mean the design of “wind resistant structures” but also, f.e.,the design of building arrangements and urban plans to minimise discomfort & pollution. • quality of life and wind-born pollution: • moderate wind risk • wind flows around buildings, interference and flow disturbance • high pedestrian level wind speed areas  social-economic negative effects on the use of such spaces • transport of air pollutants: “vulnerability” refers in this regard to health and welfare of human life (s., f.e. release of poisonous chemical gases, high traffic induced pollution, particulate emission from industry) • negative effects of noise barriers at street borders

24. OTHER TYPES OF (EOLIAN) RISK -3- • need of developing means by which the risk of unacceptable or inconvenient concentrations of pollutants cane be predicted, and remedies can be designed. It is mandatory to consider the whole range of winds (from calm to storm) and to include wind directions in the statistic data • accurate knowledge of the flow field • suitable model of the diffusion process

25. THE USE OF EXPERIMENTAL PREDICTIONS • Wind flow effects can be investigated by using following (physical and numerical) experimental methods: • Wind tunnel experiments using a uniform flow • Wind tunnel experiments using a simulated natural wind (BLWT, Boundary-Layer-Wind Tunnel) • Full-scale tests • Numerical calculations through Computational Fluid Dynamics (CFD) • Numerical simulations of the relevant stochastic processes (wind velocity, pressures or forces), based upon information on statistical parameters of the process • Each one of the above mentioned approaches shows some disadvantages because of the “partial” reproduction of the complex phenomena involving fluid-structure interaction • More detailed results could be obtained by “combining” some of the techniques, in order to get more reliable predictions

26. MITIGATION OF EOLIAN RISK & INT. RESEARCH • Overall damage can be mitigated byminimizing the hazard (how is it possible?) and, of course, by: • minimizing the exposure (less engineering task), through: • urban planning policy improvement • socio-economic growth and awareness • …… •  minimizing the vulnerability • of engineering facilities (damage risk) • of “low wind” induced effects (dissatisfaction risk) •  improving internationalawareness & research • IAWE “Storm shelter project”, Europe-Africa task force • COST Action C14 (Impact of wind & storms…) • FP6 actions (in progress)

27. CONCLUSIONS • “Is eolian risk as significant.....?”: THE ANSWER IS: YES (AT LEAST: IT SHALL BECOME SO!) • Even if Europe is a continent immune from the great tropical catastrophes, socio-economic losses & problems caused by winds cannot be neglected in a rational planning of our environment • For a number of different reasons, each one of the 3 factors of eolian risk (vulnerability, exposure and hazard) issteadily increasing • Increasing emission of harmful gases and new sensitivities as to standard of “quality of life” associate wind climate to new types of risk (dissatisfaction risk) • Sensitivity towards “wind-oriented design” must become part of the cultural background of engineers, town planners, architects and policy makers in general, also in regions with “well behaving” wind climate!

28. UNIVERSITÀ DI FIRENZE Dottorato Internazionale Congiunto   TU C.-W. ZU BRAUNSCHWEIG Europ. Graduiertenkolleg IS EOLIAN RISK AS SIGNIFICANT AS OTHER ENVIRONMENTAL RISKS? G. Augusti, C. Borri & G. Bartoli CRIACIV Firenze/Prato, March 2nd, 2002