The risk of ‘cascading’ natural disasters is rising

A man watches wildfires in California, 2013. Image: Getty.

In a warming world, the dangers from natural disasters are changing. In a recent commentary, we identified a number of costly and deadly catastrophes that point to an increase in the risk of “cascading” events – ones that intensify the impacts of natural hazards and turn them into disasters.

Multiple hazardous events are considered cascading when they act as a series of toppling dominoes, such as flooding and landslides that occur after rain over wildfires. Cascading events may begin in small areas but can intensify and spread to influence larger areas.

This rising risk means decision-makers, urban planners and risk analysts, civil engineers like us and other stakeholders need to invest more time and effort in tracking connections between natural hazards, including hurricanes, wildfires, extreme rainfall, snowmelt, debris flow, and drought, under a changing climate.

Cascading disasters

Since 1980 to January 2018, natural disasters caused an inflation-adjusted $1,537.4bn in damages in the United States.

The loss of life in that period – nearly 10,000 deaths – has been mounting as well. The United States has seen more billion-dollar natural disaster events recently than ever before, with climate models projecting an increase in intensity and frequency of these events in the future. In 2017 alone, natural disasters resulted in $306bn losses, setting the costliest disaster year on record.

We decided it was important to better understand cascading and compound disasters because the impacts of climate change can often lead to coupled events instead of isolated ones. The United Nations Office for Disaster Risk Reduction, or UNISDR, claims: “Any disaster entails a potentially compounding process, whereby one event precipitates another.”

For example, deforestation and flooding often occur together. When vegetation is removed, top soil washes away and the earth is incapable of absorbing rainfall. The 2004 Haiti flood that killed more than 800 people and left many missing is an example of this type of cascading event. The citizens of the poverty-stricken country destroyed more than 98 per cent of its forests to provide charcoal for cooking. When Tropical Storm Jeanne hit, there was no way for the soil to absorb the rainfall. To further complicate existing issues, trees excrete water vapor into the air, and so a sparser tree cover often yields less rain. As a result, the water table may drop, making farming, which is the backbone of Haiti’s economy, more challenging.

Rising risk from climate change

Coupled weather events are becoming more common and severe as the earth warms. Droughts and heatwaves are a coupled result of global warming. As droughts lead to dry soils, the surface warms since the sun’s heat cannot be released as evaporation. In the United States, week-long heatwaves that occur simultaneously with periods of drought are twice as likely to happen now as in the 1970s.

Also, the severity of these cascading weather events worsens in a warming world. Drought-stricken areas become more vulnerable to wildfires. And snow and ice are melting earlier, which is altering the timing of runoff. This has a direct relationship with the fact that the fire season across the globe has extended by 20 per cent since the 1980s. Earlier snowmelt increases the chance of low flows in the dry season and can make forests and vegetation more vulnerable to fires.

These links spread further as wildfires occur at elevations never imagined before. As fires destroy the forest canopy on high mountain ranges, the way snow accumulates is altered. Snow melts faster since soot deposited on the snow absorbs heat. Similarly, as drought dust is released, snow melts at a higher rate as has been seen in the Upper Colorado River Basin.

Fluctuations in temperature and other climatic patterns can harm or challenge the already crumbling infrastructure in the United States: the average age of the nation’s dams and levees is over 50 years. The deisgn of these aging systems did not account for the effects of cascading events and changes in the patterns of extreme events due to climate change. What might normally be a minor event can become a major cause for concern such as when an unexpected amount of melt water triggers debris flows over burned land.

There are several other examples of cascading disasters. In July, a deadly wildfire raged through Athens killing 99 people. During the same month on the other side of the world in Mendocino, California, more than 1,800 square kilometers were scorched. For scale, this area is larger than the entire city of Los Angeles.

When landscapes are charred during wildfires, they become more vulnerable to landslides and flooding. In January of this year, a debris flow event in Montecito, California killed 21 people and injured more than 160. Just one month before the landslide, the soil on the town’s steep slopes were destabilised in a wildfire. After a storm brought torrential downpours, a 5-meter high wave of mud, tree branches and boulders swept down the slopes and into people’s homes.

Hurricanes also can trigger cascading hazards over large areas. For example, significant damages to trees and loss of vegetation due to a hurricane increase the chance of landslides and flooding, as reported in Japan in 2004.

Future steps

Most research and practical risk studies focus on estimating the likelihood of different individual extreme events such as hurricanes, floods and droughts. It is often difficult to describe the risk of interconnected events especially when the events are not physically dependent. For example, two physically independent events, such as wildfire and next season’s rainfall, are related only by how fire later raises the chances of landslide and flooding.

As civil engineers, we see a need to be able to better understand the overall severity of these cascading disasters and their impacts on communities and the built environment. The need is more pronounced considering the fact that much of the nation’s critical infrastructure is aged and currently operate under rather marginal conditions.

A first step in solving the problem is gaining a better understanding of how severe these cascading events can be and the relationship each occurrence has with one another. We also need reliable methods for risk assessment. And a universal framework for addressing cascading disasters still needs to be developed.

A global system that can predict the interactions between natural and built environments could save millions of lives and billions of dollars. Most importantly, community outreach and public education must be prioritised, to raise awareness of the potential risks cascading hazards can cause.

The Conversation

Farshid Vahedifard, CEE Advisory Board Endowed Professor and Associate Professor of Civil and Environmental Engineering, Mississippi State University and Amir AghaKouchak, Associate Professor of Civil & Environmental Engineering, University of California, Irvine.

This article is republished from The Conversation under a Creative Commons license. Read the original article.


What’s killing northerners?

The Angel of the North. Image: Getty.

There is a stark disparity in wealth and health between people in the north and south of England, commonly referred to as England’s “north-south divide”. The causes of this inequality are complex; it’s influenced by the environment, jobs, migration and lifestyle factors – as well as the long-term political power imbalances, which have concentrated resources and investment in the south, especially in and around London.

Life expectancy is also lower in the north, mainly because the region is more deprived. But new analysis of national mortality data highlights a shockingly large mortality gap between young adults, aged 25 to 44, living in the north and south of England. This gap first emerged in the late 1990s, and seems to have been growing ever since.

In 1995, there were 2% more deaths among northerners aged 25 to 34 than southerners (in other words, 2% “excess mortality”). But by 2015, northerners in this age group were 29% more likely to die than their southern counterparts. Likewise, in the 35 to 44 age group, there was 3% difference in mortality between northerners and southerners in 1995. But by 2015, there were 49% more deaths among northerners than southerners in this age group.

Excess mortality in the north compared with south of England by age groups, from 1965 to 2015. Follow the lines to see that people born around 1980 are the ones most affected around 2015.

While mortality increased among northerners aged 25 to 34, and plateaued among 35 to 44-year-olds, southern mortality mainly declined across both age groups. Overall, between 2014 and 2016, northerners aged 25 to 44 were 41% more likely to die than southerners in the same age group. In real terms, this means that between 2014 and 2016, 1,881 more women and 3,530 more men aged between 25 and 44 years died in the north, than in the south.

What’s killing northerners?

To understand what’s driving this mortality gap among young adults, our team of researchers looked at the causes of death from 2014 to 2016, and sorted them into eight groups: accidents, alcohol related, cardiovascular related (heart conditions, diabetes, obesity and so on), suicide, drug related, breast cancer, other cancers and other causes.

Controlling for the age and sex of the population in the north and the south, we found that it was mostly the deaths of northern men contributing to the difference in mortality – and these deaths were caused mainly by cardiovascular conditions, alcohol and drug misuse. Accidents (for men) and cancer (for women) also played important roles.

From 2014 to 2016, northerners were 47% more likely to die for cardiovascular reasons, 109% for alcohol misuse and 60% for drug misuse, across both men and women aged 25 to 44 years old. Although the national rate of death from cardiovascular reasons has dropped since 1981, the longstanding gap between north and south remains.

Death and deprivation

The gap in life expectancy between north and south is usually put down to socioeconomic deprivation. We considered further data for 2016, to find out if this held true for deaths among young people. We found that, while two thirds of the gap were explained by the fact that people lived in deprived areas, the remaining one third could be caused by some unmeasured form of deprivation, or by differences in culture, infrastructure, migration or extreme weather.

Mortality for people aged 25 to 44 years in 2016, at small area geographical level for the whole of England.

Northern men faced a higher risk of dying young than northern women – partly because overall mortality rates are higher for men than for women, pretty much at every age, but also because men tend to be more susceptible to socioeconomic pressures. Although anachronistic, the expectation to have a job and be able to sustain a family weighs more on men. Accidents, alcohol misuse, drug misuse and suicide are all strongly associated with low socioeconomic status.

Suicide risk is twice as high among the most deprived men, compared to the most affluent. Suicide risk has also been associated with unemployment, and substantial increases in suicide have been observed during periods of recession – especially among men. Further evidence tells us that unskilled men between ages 25 and 39 are between ten and 20 times more likely to die from alcohol-related causes, compared to professionals.

Alcohol underpins the steep increase in liver cirrhosis deaths in Britain from the 1990s – which is when the north-south divide in mortality between people aged 25 to 44 also started to emerge. Previous research has shown that men in this age group, who live in the most deprived areas, are five times more likely to die from alcohol-related diseases than those in the most affluent areas. For women in deprived areas, the risk is four times greater.

It’s also widely known that mortality rates for cancer are higher in more deprived areas, and people have worse survival rates in places where smoking and alcohol abuse is more prevalent. Heroin and crack cocaine addiction and deaths from drug overdoses are also strongly associated with deprivation.

The greater number of deaths from accidents in the north should be considered in the context of transport infrastructure investment, which is heavily skewed towards the south – especially London, which enjoys the lowest mortality in the country. What’s more, if reliable and affordable public transport is not available, people will drive more and expose themselves to higher risk of an accident.

Deaths for young adults in the north of England have been increasing compared to those in the south since the late 1990s, creating new health divides between England’s regions. It seems that persistent social, economic and health inequalities are responsible for a growing trend of psychological distress, despair and risk taking among young northerners. Without major changes, the extreme concentration of power, wealth and opportunity in the south will continue to damage people’s health, and worsen the north-south divide.

The Conversation

Evangelos Kontopantelis, Professor in Data Science and Health Services Research, University of Manchester

This article is republished from The Conversation under a Creative Commons license. Read the original article.