Have We Increased our Vulnerability to Big Floods?

By Chas Keys.

In New Orleans: 11 Years after Katrina (Briefing Note 317: May 2016), John McAneney and Foster Langbein cite an observation from sociologist Shirley Laska, Professor Emerita at the University of New Orleans. Laska argues that decisions and actions taken over three centuries had reduced the vulnerability of the city of New Orleans to small and moderate floods but increased its vulnerability to very large ones. The reduction of sediment loads in the Mississippi River had led to the destruction of the marshlands and barrier islands that once protected the city from storm surges. The import of this was that ‘routine’ floods were kept out of built-up areas by the levees but the reduction of the coastal landmass increased the likelihood of the embankments being overwhelmed when very big floods struck. The disaster that was Hurricane Katrina, which led to the breaching of the levees and well over a thousand deaths, supports Laska’s point.

Laska piqued a thought that I have long harboured about flood management in NSW. We have, over the past 60 years, invested heavily in mitigating the effects of the flood threat. Much has been achieved and dozens of communities are now better off than they once were in terms of exposure to flooding. Structural protection by way of levees, flood bypasses, the rock-armouring of stream banks and the construction of mitigation dams and retarding basins has been much improved as have warning services, rescue and other response capabilities, land use management, better flood modelling, insurance coverage and, to a degree, community education about flooding and the steps people can take to manage it in their own interests. Without doubt, communities are more able to live with the flood threat created by virtue of their locations and developmental histories.

But what, precisely, is the nature of the improvement? Laska’s thinking provides a clue. What NSW has done since the late 1950s has contributed greatly to the mitigation of the effects of modest sized floods, which for many urban communities, have ceased to exist: they have been contained to nearby rural areas. But bigger, less frequent, floods are the most consequential in terms of loss of life and damage to private and public assets. No levees can be guaranteed to keep out these, partly because there is never complete certainty about levee integrity and partly because very few levees are built to exclude floods larger than the 1-in-100 year event. At the same time, we have not accompanied our engineering efforts with measures to ensure that community members understand the level of protection provided and what incomplete protection inevitably means.

In effect we have allowed, indeed encouraged, people to believe that the levees have overcome the flood problem and made it benign. This is not true.

Take the case of Maitland. On the Hunter River, its Central Business District, and more than 3000 residents in central and South Maitland, Horseshoe Bend, Lorn and part of East Maitland, are protected by levees. With the exception of Lorn, which has experienced inundation only once in more than a century, these areas have long flood histories with many killed and much property damage over the decades. The period 1949-55 saw parts of these areas flooded several times, catastrophically so in 1955, and Maitland became part of the reason that drew the state government and then the commonwealth into the field of flood mitigation. Hitherto, flood mitigation (along with warning and response) had been the responsibility of private and local council efforts and local funding. Often, it was managed poorly.

Maitland’s modern flood mitigation scheme was completed in about 1970 and has done a fine job of protecting the community from floods that have flowed past, rather than into the built-up areas. Some areas would have experienced inundation several times had the primitive levees of previous times not been superseded by well-engineered ones after the floods of the 1950s.

None of these recent floods, however, has come close in peak height or volume to those of the February, 1955 flood. That event, if repeated today, would overtop some of the levees and inundate much of urban Maitland. The so-called ‘ring levee’ which partly surrounds the town on its southern edge is designed to be overtopped in a 1-in-50 year flood, half a metre lower than the 1955 flood, which is thought likely to be equalled or exceeded only in a 1-in-200 year flood (AEP = 0.5%).

The problem is that there is a strong feeling in the community that the levees have rendered Maitland flood-free. (Andrew Gissing and his team at Risk Frontiers have seen the same sentiments expressed in Lismore.) The fact that the ring levee is designed to admit floodwaters in floods much smaller than the 1955 event is unknown to many, probably most. One indication of this was in 2007, when a flood for a time thought likely by the Bureau of Meteorology to be the highest since 1955, produced a rather desultory property protection and evacuation response from many members of the community.

During the 1950s, with flood after flood assailing them, Maitlanders became expert at neighbourhood-level self-help endeavours like lifting furniture in situ, trucking it to the nearby hill suburbs of East Maitland and Telarah and evacuating people to safety. Some had to evacuate eight times between 1949 and 1955. Of necessity a strong flood culture existed in those days as it had in earlier times. When floods were approaching, groups of men would move from house to house, helping residents lift furniture and other home contents or carrying them out to drays and trucks for transporting to the nearby hill suburbs. Families followed, staying with friends and relatives while waiting for the floodwaters to recede.

Since the 1950s only two floods have produced forecasts that would have justified raising or removing belongings and leaving for high ground. These were the floods of 1971 (peaking nearly a metre lower than in 1955 and coming close to overtopping the ring levee) and 2007 (when the peak, thought initially to have been likely to slightly exceed that of 1971, turned out to have been substantially over-predicted). On the evidence of 2007, a big flood now would see a substantial under-response on behalf of community members, with material damage and perhaps deaths higher than would have been the case had the the behavioural modes of the 1950s been in place.

And there is further reason for pessimism about Maitland: the local council, in its concern about the commercial viability of the Central Business District, has sought to reverse some of the land use restrictions that have been in place since the 1950s. The ‘old city’ has lost population steadily over the decades through out-migration and the expansion of commercial land uses into residential areas, and the CBD’s market has shrunk considerably. To bolster the viability of the CBD the council now seeks to restore the residential population of nearby areas to the level of 1954, when well over 5000 people lived in them compared with fewer than 1800 today.

Faced with severe state-instituted restrictions on building in these areas, the council proposed in 2015 that the restrictions on residential floor height construction in levee-protected areas be abandoned provided that new dwellings were built with at least 50% of their habitable flood space above the flood standard (the modelled 1-in-100 year flood level plus half a metre freeboard). The reasoning was that residents, on hearing a flood forecast and being advised to raise items of value, would have the opportunity to move items from the lower floors of their dwellings to the higher floors.

An appeal to the state Minister for Planning for a relaxation of the building restrictions was, however, rejected. The Minister’s decision implied a recognition that the proposed change might easily have led to increased flood damage. Now the Office of Environment and Heritage has argued that new residential development − even development which adheres to the existing planning restrictions − should not be undertaken until the road infrastructure that will support evacuation from the ‘old city’ is upgraded. The council’s ambitions for population growth in the old city are being thwarted. Had the council’s preferred solution to the woes of the CBD been implemented then the community’s vulnerability to flooding would have been increased simply by virtue of many more people becoming residents of flood prone areas.

Given the reality of the flood situation, there is a strong case for community flood education to include messages about the inevitability, in very large floods, of inundation of areas behind the levees. One initiative, undertaken in the early 1980s by the Department of Public Works, involved the fixing to power poles of markers indicating the heights reached in the flood of 1955. A few of these in the built-up areas were more than four metres above ground level; many were more than two metres above. The council was never enthusiastic about the markers, and when Public Works vacated the field of flood education, they slowly disappeared ─ the victims of power pole replacement, people concerned about the value of their properties, and the rusting of the nails that held them in place. Today there are fewer than ten of the several dozen original markers left. An inexpensive, easy-to-maintain means of reminding or informing residents and others of the potential for severe flooding has gradually disappeared.

Since 2001, the State Emergency Service has assumed the role of providing community flood education. Yet these worthy efforts there is much to suggest that the community at large does not comprehend the flood risk implied by the potential for levee failure or overtopping. What we have in today’s Maitland is levees designed to let water into built-up areas in big floods, a community that is inexperienced in flood management, many residents who are oblivious to the threat that big floods pose and a council that seeks to increase the population in areas that will be severely affected by big floods and which shows little interest in flood education. This is a potentially lethal combination.

The levees have done an excellent job in protecting the community but carry the downside of an altered perception of the flood risk. The policy message is that in building levees we should also build an understanding of their limitations and stress that they can only mitigate, not eliminate, the flood threat. Co-ordinated, properly resourced and appropriately evaluated programmes seeking to do this do not exist in Australia.

The education needs to extend to elected councillors to help them understand that their decisions can contribute greatly to the oft-demonstrated ‘levee paradox’ in which the provision of structural protection too easily leads to intensified development in the protected areas. Councils are accustomed to dealing with the tension between developmental and environmental considerations, but less so in managing conflict between community safety and developmental objectives.

In New Orleans it was largely the progressive erosion of natural coastal defences that increased the city’s vulnerability to big floods. Many died in Hurricane Katrina as a consequence. In Maitland we risk the same effect being wrought. By pursuing a land use management policy that will put more people in harm’s way when big floods occur, and at the same time by not making a fully-fledged effort to ensure that people comprehend the nature of the threat posed by such floods, the level of the community’s flood vulnerability has been increased. A big flood, even one not as big as the flood of 1955, will demonstrate this some day. Maitland’s story also has the potential to be reproduced in many other leveed areas in Australia.

Happy Graduates – Stuart and Tetsuya

From left: Christina Magill, Stuart Mead, Tetsuya Okada, Kat Haynes

Congratulations to Stuart Mead and Tetsuya Okada pictured here with their supervisors Christina Magill and Kat Haynes.

Tetsuya Okada’s PhD investigated recent disaster recovery and risk reduction processes in Australia and Japan. Read more.

Stuart Mead’s PhD developed and integrated computational models of lahar hazard in order to quantify the risk and potential losses caused by lahars. Read more.

Where, Why And How Are Australians Dying In Floods?

This article by Freya Jones, published in Asia Pacific Fire Magazine, October 3, refers to research undertaken the CRC research team led by Katharine Haynes, Risk Frontiers.

Fatalities from floods are a major cause of natural hazard deaths around the globe. Here in Australia, floods are ranked second only to heatwaves in terms of the total number of natural hazard fatalities since 1900. Recent cases over the last two years, such as June 2016 in New South Wales and Tasmania, along with the aftermath of Severe Tropical Cyclone Debbie in northern NSW in April this year, highlight the significant dangers of floodwaters and as the research suggests, many of the flood deaths are avoidable.

To gain a greater understanding of human behaviour and why people choose to enter floodwaters, the CRC research project Analysis of human fatalities and building losses from natural disasters has measured the impacts of floods. The research looks at the toll on human life, injuries and building damage while analysing trends over time. Read more.

A Machine Learning Model Of Tropical Cyclone Wind Risk

This article by Thomas Loridan, Risk Frontiers, was published in Asia Pacific Fire Magazine, October 3, 2017.

Extreme winds from tropical cyclones (TCs) regularly threaten communities worldwide. In recent decades significant efforts have been put towards improving our understanding of the mechanisms involved. In particular detailed analysis of satellite imagery and observations from aircraft reconnaissance missions have allowed formulation of a well-accepted framework whereby asymmetries in the TC wind field structure are attributed to the forward motion of the system: stronger winds occur to the right (left) of a moving TC in the northern (southern) hemisphere with the magnitude of the left/right asymmetry increasing as the storm moves faster. Read more.

Disaster Risk Management: Australian Challenges

This article by Andrew Gissing, Risk Frontiers, was published in Asia Pacific Fire Magazine, October 3, 2017.

Australia is exposed to a variety of natural and technological disaster risks, which vary in their significance across the nation. Communities are faced with the increasing costs of disaster losses due to higher wealth and the increasing development of hazardous areas, whilst Government budgets are under pressure. Climatic, demographic, economic, political and technological changes are acting to shape future disaster risks.

Internationally, the Sendai Framework for Disaster Risk Reduction exists with the goal to: “prevent new and reduce existing disaster risk through the implementation of integrated and inclusive economic, structural, legal, social, health, cultural, educational, environmental, technological, political and institutional measures that prevent and reduce hazard exposure and vulnerability to disaster, increase preparedness for response and recovery, and thus strengthen resilience”.  Read more.

Could Sydney be the next Houston?

Andrew Gissing and Dr Chas Keys.

Devastating floods have occurred last month in Texas, USA, inundating large parts of America’s fourth largest city, Houston, as a consequence of Hurricane Harvey. Thousands of people have required rescue, and as of the 14th of September 82 people had died. It had been some ten years since a large hurricane had crossed the US Gulf Coast. Much of the blame for the disaster is being placed on the significant increases in urban development in flood liable areas.

According to research by the Bushfire and Natural Hazards Research Centre and Risk Frontiers, flooding in Australia has been the second largest contributor to natural hazard deaths since 1900, behind fatalities attributed to heatwaves. The Productivity Commission in 2014 reported that Australian floods have also contributed over five billion dollars in damages between 1970 and 2013.

Is Australia’s largest city, Sydney, prone to similar catastrophic flooding scenarios in the future? Sydney has a different geography and climate to Houston but has numerous populated river and creek catchments that have experienced flooding historically, but not for some time. A possible Sydney flood scenario would see heavy rainfall from perhaps a severe east coast low pressure system first drenching the city’s impervious streets and small creek and river catchments, resulting in significant stormwater and flash flooding. This flooding would occur with little specific warning, but rapidly subside. The greater metropolitan area has seen significant flash flooding before as a result of severe rainfall in 1984, 1986 and 1988. Areas that could be impacted include the northern beaches, eastern suburbs (Randwick and Rose Bay), the Inner West (Marrickville, Strathfield, Canterbury and Annandale), Parramatta, Ryde, Woronora and Fairfield areas. The impacts would significantly disrupt the city’s transport systems and undoubtedly lead to countless flood rescues.

Following initial flash flooding, rivers could rise to severe levels, threatening communities along the Georges, Hawkesbury and Nepean Rivers, necessitating large scale evacuations across the southwest and western parts of the city. These areas were hit by severe flooding in 1867, and experienced major flooding in the 1980s and 1990. If similar flood levels to 1867 were to occur today, over 11,000 homes could be flooded in western and south western Sydney, their occupants requiring evacuation. Essential infrastructure would be damaged resulting in disruption to transport, energy, water supply and businesses for days to weeks following. It would take those affected years to recover. More extreme flood events are also possible.

Other communities outside of Sydney could be impacted too. The 1867 event also affected Wollongong, Nowra, Moruya, Tamworth, Bathurst, Mudgee, Dubbo, Forbes and Wagga Wagga (Yeo et al., 2017). Such a scenario would place significant demand on the state’s emergency services.

Unlike the current experience of Houston, local governments in New South Wales do regulate development of flood prone areas with a policy of ensuring new development is limited to areas outside zones which would likely be flooded, on average, once every hundred years. This standard, however, does not provide immunity against larger flood events, which may include some high risk areas and many properties.

There are still large legacy issues in areas that have already been developed. The NSW Government has recently released a flood management strategy to tackle flood risk along the Hawkesbury and Nepean rivers. In other areas, local government complete floodplain risk management plans detailing intended methods to address flood risk.

Flood risk management is a game of balance, requiring the careful management of what can often be competing objectives of building prosperous communities where there are economic opportunities versus maintaining public safety and the resilience of the community. To avoid the amplification of flood risk and suffering experienced in Houston, land use planning controls will remain key.

It has been some time between large floods in Sydney, with communities becoming largely apathetic towards the risk. It is, however, inevitable that they will return. The risk is serious, requiring both prudent flood risk management by governments and action by individuals to ensure household and business preparedness.

For more information please contact Andrew at andrew.gissing@riskfrontiers.com

References

YEO, S., BEWSHER, D., ROBINSON, J. & CINQUE, P. 2017. The June 1867 floods in NSW: causes, characteristics, impacts and lessons. Floodplain Management Australia National Conference. Newcastle, NSW.

 

 

Bridging the divide between studies on disaster risk reduction education and child-centred disaster risk reduction – a critical review

There has been a recent increase in the body of knowledge related to children and disasters. These studies converge into three main fields of research: the impact of disasters on children and their psychological recovery, the integration of disaster risk reduction (DRR) into the education sectors and children’s participation in DRR. This article provides a literature review of the two latter fields of research where the focus is on reducing disaster losses and building resilience prior to a disaster. Overall, 48 studies are critically reviewed and compared in relation to the strengths and weaknesses of their aims, methods, locations of research, impact, and outcomes. The review identified a number of differences between the two fields and significant opportunities for linking the two approaches, sharing lessons and knowledge. Based on the review, recommendations for further research are outlined.

read more

Newsletter Volume 17, Issue 1 – August 2017

In this issue:

  • A Natural Hazard Building Loss Profile for Australia: 1900-2015
  • Risk Frontiers’ Annual Seminar: A Provisional Programme
  • Weather-related Natural Disasters: Should we be concerned about a reversion to the mean?

A Natural Hazard Building Loss Profile for Australia: 1900-2015

J McAneney¹,², N Madappatt¹, L Coates¹,² R Crompton¹,² R D’Arcy¹ and R Blong¹
¹Risk Frontiers, Macquarie University, NSW 2019
²Bushfire &Natural Hazards Cooperative Research Centre

This study examined building damage as recorded in PerilAUS (e.g. Coates et al. (2014)) to determine the national profile of natural peril impacts and frequencies. The analysis employed Risk Frontiers’ Damage Index based on a House Equivalent (HE) loss metric introduced by Blong (2003); a simple normalisation correction based on Crompton et al. (2010) and a lower bound event threshold of 25 normalised HE. The latter is equivalent to a monetary loss of around $10m in 2015-16. Normalisation puts historical events on a common footing with losses that would be incurred given 2015 societal and demographic conditions; it answers the question: what would be the losses if historic events were to recur today?

While more analysis remains to be done to validate the HE calculations and the spatial distribution of losses across States and Territories, we find that there have been on average 5.85 events per year causing losses in excess of 25 normalised HE (Figure 1). This frequency exhibits no statistically significant change since 1900. The mean loss per event is $118m with a standard deviation of $430m. The absence of a trend over time is insensitive to the threshold HE employed.

Figure 1: Number of events per financial year (July 1 to June 30) causing normalised building losses in excess of $10m. Events are grouped by financial year to discriminate between Southern Hemisphere summers when many weather-dependent events occur.

The most costly event in terms of building damage is the 1999 Sydney hailstorm, which was also the most expensive insured loss. The losses broadly follow a Pareto distribution in which 20% of events account for 80% of the aggregated normalised building losses and the top 20 are responsible for 50% of those losses. We can expect natural disaster events as costly as the 1999 Sydney hailstorm

to occur about once per century, events like the Brisbane floods once every 30 to 40 years and that of the Hobart Bushfires about once a decade.

Figure 2: The top 300 normalised losses against rank. The straight line shows a Pareto (power law) distribution.

The pattern of losses shown in Figure 2 demonstrates the ‘heavy-tailed’ character of the natural peril losses where there is always the possibility of event losses far in excess of the historical mean. This may occur because of an event of higher intensity or larger footprint, that footprint impacting an area of higher-valued exposure, or all of these together.

A preliminary breakdown of damage by perils shows tropical cyclones to have been most destructive and responsible for 30% of the national building damage since 1900. Bushfires, floods and hail have all been similarly costly each accounting for another 18% of building losses, although when hailstorms are combined with other storm events (excluding cyclones), thunderstorms similarly contribute 30% of the losses. Compared with meteorological hazards, geophysical perils have had a minor influence on building damage over the last 116 years with earthquake losses dominated by a single event — the 1989 Newcastle earthquake. However this time period is too short to predict the frequency of damaging seismic events and, in the case of this peril, as with some others, the spatial pattern of losses shown here could be overturned by another extreme event loss.

While we believe the above results to be robust, further validation of the House Equivalent calculations is required with particular scrutiny on Central Damage Value estimates by peril. Ongoing work will undertake a comparison with the normalised ICA Disaster List (Crompton and McAneney 2008) once this has been updated by Risk Frontiers later this year and with insurance claims information for key events.

References

Blong RJ (2003) A new damage index, Natural Hazards, 30, 1-23.

Coates L, Haynes KA, O’Brien J, McAneney KJ and Dimer de Oliveira F (2014) Exploring 167 years of vulnerability: An examination of extreme heat events in Australia 1844-2010, Environmental Science and Policy, 42, 33-44. DOI: 10.1016/j.envsci.2014.05.003.

Crompton RP and McAneney KJ (2008) Normalised Australian insured losses from meteorological hazards: 1967-2006 Environ, Science & Policy 11 (5), 371-378.

Crompton RP, McAneney KJ, Chen K, Pielke Jr RA and Haynes KA (2010) Influence of location, population, and climate on building damage and fatalities due to Australian bushfire: 1925-2009, Weather, Climate and Society, 2, 300-310.

Risk Frontiers’ Annual Seminar: A Provisional Programme

Thursday 12th October, 2017, commencing 2.00pm at the Museum of Sydney, cnr Phillip & Bridge Streets, Sydney

And on the menu:

Long-term natural records of tropical cyclones
This year’s guest speaker, Professor Jonathon Nott, is a geoscientist who, inter alia, has reconstructed long term records of extreme storm surge events on the Australian coastline. Come and learn how representative is the recent satellite era of the longer-term history of landfalling cyclones.

Synthesis of Risk Frontiers’ social research findings
Andrew Gissing distils key learnings in context of fire, flood, heatwave and tropical cyclone events.

Vignettes de recherche
Listen to Lucinda Coates on our updated PerilAUS record of deaths from natural hazard events and Tahiry Rabehaja on how to update the updating of PerilAUS. Thomas Mortlock will talk about coastal erosion and TC Debbie while Mingzhu Wang explains how machine-learning techniques are improving FireAUS.

Seasonal drivers of bushfire weather risks in SE Australia
Stuart Browning goes back to 1851 and further still to develop a long-term history of bushfire climate risks.

And did I mention it? There are drinks as well!!

Invitations will be distributed shortly and are also available on our website: riskfrontiers.com.au

Weather-related Natural Disasters: Should we be concerned about a reversion to the mean?

Professor Roger Pielke Jr (University of Colorado, Boulder)

The world is presently in an era of unusually low weather disasters. This holds for the weather phenomena that have historically caused the most damage: tropical cyclones, floods, tornadoes and drought. Given how weather events have become politicized in debates over climate change, some find this hard to believe. Fortunately, government and IPCC (Intergovernmental Panel on Climate Change) analysis allow such claims to be adjudicated based on science, and not politics.  Here I briefly summarize recent relevant data.The world is presently in an era of unusually low weather disasters. This holds for the weather phenomena that have historically caused the most damage: tropical cyclones, floods, tornadoes and drought. Given how weather events have become politicized in debates over climate change, some find this hard to believe. Fortunately, government and IPCC (Intergovernmental Panel on Climate Change) analysis allow such claims to be adjudicated based on science, and not politics.  Here I briefly summarize recent relevant data.

Every six months Munich Re publishes a tally of the costs of disasters around the world for the past half year. This is an excellent resource for tracking disaster costs over time.  The data allows us to compare disaster costs to global GDP, to get a sense of the magnitude of these costs in the context of economic activity.  Using data from the UN, Figure 1 shows how that data looks since 1990, when we have determined that data is most reliable and complete.

The data shows that since 2005 the world has had a remarkable streak of good luck when it comes to big weather disasters, specifically:

  • From 2006 to present there have been 7/11 years with weather disasters costing less than 0.20% of global GDP.
  • The previous 11 years saw 6 with more than 0.20% of global GDP.
  • From 2006 to present there has been zero years with losses greater than 0.30% of global GDP.
  • The previous 11 years had 2, as did the 6 years before that, or about once every 4 years.
  • According to a simple linear trend over this time period, global disasters are 50% what they were 27 years ago, as a proportion of GDP.

Why has this occurred? Is it good luck, climate change or something else?

By disaggregating the data phenomenon by phenomenon we can get a better sense of why it is that disaster costs are, as a proportion of global GDP, so low in recent years.

Figure 1

A good place to start is with tropical cyclones, given that they are often the most costly weather events to occur each year. Figure 2 shows global tropical cyclone landfalls from 1990 through 2016. These are the storms that cause the overwhelming majority of property damage. Since 1990 there has been a reduction of about 3 landfalling storms per year (from ~17 to ~14), which certainly helps to explain why disaster losses are somewhat depressed.

Figure 2

Even more striking is the extended period in the United States, which has the most exposure to tropical cyclone damage, without the landfall of an intense hurricane. Figure 3 shows the number of days between each landfall of a Category 3+ hurricane in the US, starting in 1900. As of this writing the tally is approaching 4500 days, which is a streak of good fortune not seen in the historical record.

Figure 3

A very conservative estimate of the effects of this “intense hurricane drought” is that the United States is some $70 billion in arrears with respect to expected hurricane damage since 2006. In fact, it is not widely appreciated but the US has seen a decrease of about 20% in both hurricane frequency and intensity at landfall since 1900. I urge caution placing too much significance on linear trends, as they are quite sensitive to start and end dates, but there is very little to indicate that tropical cyclones are either more frequent or intense.

Data on floods, droughts and tornadoes are similar in that they show little to no indication of becoming more severe or frequent.  The IPCC concludes:

  • “There continues to be a lack of evidence and thus low confidence regarding the sign of trend in the magnitude and/or frequency of floods on a global scale.”
  • “There is low confidence in observed trends in small spatial-scale phenomena such as tornadoes and hail.”
  • “There is low confidence in detection and attribution of changes in drought over global land areas since the mid-20th century.

”Thus, it is fair to conclude that the costs of disasters worldwide is depressed because, as the global economy has grown, disaster costs have not grown at the same rate. Thus, disaster costs as a proportion of GDP have decreased. One important reason for this is a lack of increase in the weather events that cause disasters, most notably, tropical cyclones worldwide and especially hurricanes in the United States.

Climate change, of course, is all too real and has a significant human component. The IPCC has concluded that there is evidence indicating that heatwaves have become more common as too has extreme rainfall in some parts of the world.  Projections for the future suggest that some other types of extremes – including tropical cyclones, floods, drought and tornadoes – may yet become more intense or frequent. However, there is great uncertainty about how extremes will evolve in the climate future.

But we don’t need climate scenarios to be worried about more disasters. To the extent that people believe that we are presently in an era of large or unusual disasters, many will be in for a shock when large weather disasters again occur. And they will. A simple regression to the mean would imply disasters of a scale not seen worldwide in more than a decade.

Consider that 2005 saw weather disasters totaling 0.5% of global GDP. In 2017, if the world economy totaled $90 trillion (in a round number), then an equivalent amount of 2017 disaster losses to the proportional costs to 2005 GDP would be about $450 billion. That is about equivalent to Hurricane Katrina, Superstorm Sandy, Hurricane Andrew, the 2011 Thailand floods, the 1998 Yangtze floods all occurring in one year plus about $100 billion more in other disaster losses. And there is no reason why we should consider 0.5% of GDP to be an upper limit. Think about that.

The world has had a run of good luck when it comes to weather disasters. That will inevitably come to an end. Understanding loss potential in the context of inexorable global development and long term climate patterns is hard enough.  It is made even more difficult with the politicized overlay that often accompanies the climate issue. Fortunately, there is good science and solid data available to help cut through the noise. Bigger disasters are coming – will you be ready?

Sources

Mohleji S, & Pielke Jr R (2014). Reconciliation of trends in global and regional economic losses from weather events: 1980–2008. Natural Hazards Review, 15(4), 04014009.

Munich Re (2017)  Natural catastrophe review for the first half of 2017 https://www.munichre.com/en/media-relations/publications/press-releases/2017/2017-07-18-press-release/index.html

Murray V, & Ebi KL (2012). IPCC special report on managing the risks of extreme events and disasters to advance climate change adaptation (SREX).

Pielke Jr R (2014) The rightful place of science: disasters and climate change. (CSPO: ASU)

Stocker TF, et al. (2013) IPCC, 2013: climate change 2013: the physical science basis. Contribution of working group I to the fifth assessment report of the intergovernmental panel on climate change.

Weinkle J, Maue R, & Pielke Jr, R. (2012) Historical global tropical cyclone landfalls. Journal of Climate, 25:4729-4735.

Earth’s rotation affects the wide world of sports

Ryan Crompton and Paul Somerville, Risk Frontiers.


Newton’s laws of motion describe the motion of an object in an inertial (non-accelerating) frame of reference. When Newton’s laws are transformed to a rotating frame of reference (such as the earth’s surface), the Coriolis force and centrifugal force appear.  These forces are important in oceans and atmospheres. As water or air moves away from the equator toward the poles, its rotation rate about the earth’s rotation axis increases to conserve angular momentum as the distance to the axis of rotation decreases. Rather than flowing directly from areas of high pressure to low pressure, as they would in a non-rotating system, winds and currents tend to flow to the right of this direction north of the equator and to the left of this direction south of it. This effect is responsible for the rotation of large cyclones and the generation of warm currents that travel north and south from equatorial waters in the western Pacific Ocean.  As described in IOP on 31 March 2017, reproduced here, these forces can also have a significant impact on sports.


The inertial forces generated by the Earth as it rotates can have an impact on sports as varied as cricket, bowls, rowing, swimming and horse racing, Australian researchers have shown.

Dr Garry Robinson, from the University of New South Wales, Canberra, and his brother Dr Ian Robinson, from Victoria University, Melbourne, looked at how the Coriolis force – which produces a sideways movement – and the centrifugal force, both resulting from the earth’s rotation, affect everything from a bowled cricket ball to a rowing scull.

They published their results today in the journal Physica Scripta. Ian Robinson said: “We wanted to explore what effect these forces would have on sports like cricket, where the ball is thrown or bowled; on golf – where the ball travels a longer distance; on lawn bowls, where accuracy is paramount; and on rowing and running, where large distances are covered.”

“Newton’s laws of motion apply in an inertial system, but our rotating Earth is not an inertial system. Two additional forces are present – the Coriolis force, and the centrifugal force. Generally, these two inertial forces produce noticeable effects only on the large scale, when either the time of travel and/or the path lengths are large – for example the Coriolis effect is extremely important for navigation.”

The researchers added both the forces to the equations of motion, and also included a ground friction-type force to simulate a ball rolling over a surface, or a body moving through something resistive like water.

Their expectation was that the effect for small-scale ball games – golf, and cricket – would be fairly small. This proved to be the case, with sideways movement for a cricketer’s throw from the boundary being less than one centimetre and less than 10 centimetres for a long drive in golf.

Garry Robinson said: “However, there were some sports where the effect was more than sufficient to make a difference to the outcome. In lawn bowls, for example, the sideways movement can be up to 2.8 centimetres, which is enough to affect the outcome of the game.

“Even more significantly, in a two kilometre rowing race the sideways movement can be up to 40 metres, if it is not compensated for, while an athlete running a four-minute mile will be subjected to a sideways movement of nearly 20 metres, again if not compensated for.

“It’s possible the participants in these sports aren’t even aware of the potential sideways effect, and could be compensating for it without knowing. Even if they are, we calculated that in the case of the rower, they will need to apply up to 7.5 per cent of their forward propulsion force to counteract it.”

Another example is found in horse racing. The Coriolis force can ‘push’ a horse towards the inner rail running in one direction, and towards the outer rail running in the opposite direction, with a potential sideways movement of up to 4 metres in a 1,200 metre sprint.

This is automatically (unknowingly) compensated for, and normally is likely to be totally masked by other effects. Nevertheless, the effects of the Coriolis force may sometimes be significant, as in some areas of the world horses run in a clockwise direction in one state, and in a counter-clockwise direction in a neighbouring state, with horses regularly moving between locations.

The researchers also noted that the matter is further complicated because the size of the effect is latitude dependent; it reverses in right/left direction in going from one hemisphere to the other; and, for a fixed hemisphere, it reverses from, for example, an east to west or north to south direction if the direction of the velocity reverses.

Ian Robinson said: “It is possible therefore, that there are subtle effects not noticed by athletes that may inhibit their performance, particularly if there is a change of venue or hemisphere.”

Weather-related Natural Disasters: Should we be concerned about a reversion to the mean?

Professor Roger Pielke Jr (University of Colorado Boulder)


Roger is a long-term Research Fellow of Risk Frontiers and recently it was our pleasure to be able to host him, once again, in Sydney. During this visit, we were rewarded with an insightful seminar entitled Natural Disasters and Climate Change: The Science and the Politics. Below is a brief synopsis of some of the key points raised in Roger’s talk. A pdf of his presentation is available for those wanting further information.

We would also direct readers to Roger’s book entitled: The Rightful Place of Science: Disasters and Climate Change as the most accessible and thoughtful compendium of research in this area and of discussion as to the correct role of science in informing political debate and policy in contentious and important areas like global climate change. (https://www.amazon.com.au/d/ebook/Rightful-Place-Science-Disasters-Climate-Change-Pielke/B00SZ83XMG/ref=sr_1_fkmr0_2?ie=UTF8&qid=1501026563&sr=8-2-fkmr0&keywords=roger+Pielke+jr).


The world is presently in an era of unusually low weather disasters. This holds for the weather phenomena that have historically caused the most damage: tropical cyclones, floods, tornadoes and drought. Given how weather events have become politicized in debates over climate change, some find this hard to believe. Fortunately, government and IPCC (Intergovernmental Panel on Climate Change) analyses allow such claims to be adjudicated based on science, and not politics.  Here I briefly summarize recent relevant data.

Every six months Munich Re publishes a tally of the costs of disasters around the world for the past half year. This is an excellent resource for tracking disaster costs over time.  The data allows us to compare disaster costs to global GDP, to get a sense of the magnitude of these costs in the context of economic activity.  Using data from the UN, here is how that data looks since 1990, when we have determined that data is most reliable and complete.

The data shows that since 2005 the world has had a remarkable streak of good luck when it comes to big weather disasters, specifically:

  • From 2006 to present there have been 7/11 years with weather disasters costing less than 0.20% of global GDP.
  • The previous 11 years saw 6 with more than 0.20% of global GDP.
  • From 2006 to present there has be zero years with losses greater than 0.30% of global GDP.
  • The previous 11 years had 2, as did the 6 years before that, or about once every 4 years.
  • According to a simple linear trend over this time period, global disasters are 50% what they were 27 years ago, as a proportion of GDP.

Why has this occurred? Is it good luck, climate change or something else?

By disaggregating the data phenomenon by phenomenon we can get a better sense of why it is that disaster costs are, as a proportion of global GDP, so low in recent years.

A good place to start is with tropical cyclones, given that they are often the most costly weather events to occur each year.  The figure below shows global tropical cyclone landfalls from 1990 through 2016. These are the storms that cause the overwhelming majority of property damage. Since 1990 there has been a reduction of about 3 landfalling storms per year (from ~17 to ~14), which certainly helps to explain why disaster losses are somewhat depressed.

Even more striking is the extended period in the United States, which has the most exposure to tropical cyclone damage, without the landfall of an intense hurricane. The figure below shows the number of days between each landfall of a Category 3+ hurricane in the US, starting in 1900. As of this writing the tally is approaching 4500 days, which is a streak of good fortune not seen in the historical record.

A very conservative estimate of the effects of this “intense hurricane drought” is that the United States is some $70 billion in arrears with respect to expected hurricane damage since 2006. In fact, it is not widely appreciated but the US has seen a decrease of about 20% in both hurricane frequency and intensity at landfall since 1900. I urge caution placing too much significance on linear trends, as they are quite sensitive to start and end dates, but there is very little to indicate that tropical cyclones are either more frequent or intense.

Data on floods, drought and tornadoes are similar in that they show little to no indication of becoming more severe or frequent.  The IPCC concludes:

  • “There continues to be a lack of evidence and thus low confidence regarding the sign of trend in the magnitude and/or frequency of floods on a global scale.”
  • “There is low confidence in observed trends in small spatial-scale phenomena such as tornadoes and hail.”
  • “There is low confidence in detection and attribution of changes in drought over global land areas since the mid-20th century.”

Thus, it is fair to conclude that the costs of disasters worldwide is depressed because, as the global economy has grown, disaster costs have not grown at the same rate. Thus, disaster costs as a proportion of GDP have decreased. One important reason for this is a lack of increase in the weather events that cause disasters, most notably, tropical cyclones worldwide and especially hurricanes in the United States.

Climate change, of course, is all too real and has a significant human component. The IPCC has concluded that there is evidence indicating that heat waves have become more common as too has extreme rainfall in some parts of the world.  Projections for the future suggest that some other types of extremes – including tropical cyclones, floods, drought and tornadoes – may yet become more intense or frequent. However, there is great uncertainty about how extremes will evolve in the climate future.

But we don’t need climate scenarios to be worried about more disasters. To the extent that people believe that we are presently in an era of large or unusual disasters, many will be in for a shock when large weather disasters again occur. And they will. A simple regression to the mean would imply disasters of a scale not seen worldwide in more than a decade.

Consider that 2005 saw weather disasters totaling 0.5% of global GDP. In 2017, if the world economy totaled $90 trillion (in a round number), then an equivalent amount of 2017 disaster losses to the proportional costs to 2005 GDP would be about $450 billion. That is about equivalent to Hurricane Katrina, Superstorm Sandy, Hurricane Andrew, the 2011 Thailand floods, the 1998 Yangtze floods all occurring in one year plus about $100 billion more in other disaster losses. And there is no reason why we should consider 0.5% of GDP to be an upper limit. Think about that.

The world has had a run of good luck when it comes to weather disasters. That will inevitably come to an end. Understanding loss potential in the context of inexorable global development and long term climate patterns is hard enough.  It is made even more difficult with the politicized overlay that often accompanies the climate issue. Fortunately, there is good science and solid data available to help cut through the noise. Bigger disasters are coming – will you be ready?

References

Mohleji, S., & Pielke Jr, R. (2014). Reconciliation of trends in global and regional economic losses from weather events: 1980–2008. Natural Hazards Review, 15(4), 04014009.

Munich Re, 2017.  Natural catastrophe review for the first half of 2017 https://www.munichre.com/en/media-relations/publications/press-releases/2017/2017-07-18-press-release/index.html

Murray, V., & Ebi, K. L. (2012). IPCC special report on managing the risks of extreme events and disasters to advance climate change adaptation (SREX).

Pielke, R. (2014). The rightful place of science: disasters and climate change. (CSPO: ASU)

Stocker, T. F., et al. (2013). IPCC, 2013: climate change 2013: the physical science basis. Contribution of working group I to the fifth assessment report of the intergovernmental panel on climate change.

Weinkle, J., Maue, R., & Pielke Jr, R. (2012). Historical global tropical cyclone landfalls. Journal of Climate, 25:4729-4735.