Flooding in Cities

Cities are complex, populous and interdependent systems which are extremely vulnerable to threats from natural hazards. Recent years have witnessed a sprawling metropolis which has fostered a large build up of highly vulnerable development (Burby, 2006). There is growing concern about placing these compact urban forms in harm's way as new urban developments are aggravating the growing risk to hazards, by adding even higher density developments than in the past. High-density developments place more people, residential and commercial buildings and infrastructure at risk if hazards are not anticipated and hazard mitigation is not prioritised. Does this trend mean that the worlds cities that accommodate a vast proportion of the population are becoming less disaster-resilient? 

Flooding in Northern England following torrential rain over the Christmas period

In terms of flooding, average economic losses alone exceed $6 billion in the US and these losses have been rising relative to increases in population! The flooding caused by Hurricane Katrina which caused over $200 billion in losses was the most costly natural disaster in US history. Coastal cities such as Bay St Louis, Pass Christian and Waveland have increased exposure to catastrophic losses from disasters and thus were nearly obliterated. Should this mass flooding serve as reminder to densely populated coastal populations around the world of their vulnerability to natural hazards?

The UK was subject to flooding across over the Christmas period: claiming lives, causing evacuations, power cuts and chaos, the costs of being under prepared for natural hazards is huge. The Environmental Agency has released another warning stating that Britain faces another month of flood and that there is 'no end in sight' to the bad weather which has disrupted festivities and already brought misery to more than 10,000 people nationwide. The following table shows the flood warnings in place across the UK as of 30/12/2013 at 12:07.

A study by Berke et al. revealed that local governments in the US give more attention to New Urban developments in applying land use regulatory and incentive techniques, public participation initiatives and technical assistances. They have been criticised for being reluctant to anticipate future risks and giving less attention to the use of non-structural mitigation techniques and storm water BMPs. Experts have suggested that more attention needs to be placed on non-structural hazard mitigation in order to counter the building of high-density developments in flood-prone areas in cities across the globe. High-quality planning would mean that attention would be paid to issues such as hazard mitigation thus losses from flooding would be lower in communities that prepare and implement plans for urban development. However this is frequently ignored and continues to occur - a clear example of this are the huge slum developments that are increasingly vulnerable to flooding. This paper looks into the responses of slum dwellers affected by flooding in India.

Looking into the future, hazard mitigation standards such as Smart Code will play a more important role. They prioritise design features such as pedestrian orientated streets, mixed land uses as well as protection of environmentally sensitive areas given their critical mitigation services. However in order to rely on environmentally sensitive natural systems such as wetlands, sand dunes and mangroves to manage and store flood waters, they must be protected. 

New urban developments are laboratories within which we can cautiously experiment with hazard mitigation and environmental protection strategies. They are a living test of how to deal with emerging hazards such as sea level rise and more intense weather events linked to global climate change.

Next time I will look at ways in which cities are acting to mitigate the impact of flooding via levees, storm surge barriers, etc. In the meantime, if you can't get enough of climate change adaptation strategies and flood risk reduction in cities be sure to check out this paper. 

A Lack of Ambition in Disaster Research?

Whilst doing some research for my next post on floods, I came across this extremely engaging post by John Twigg (2013) in his blog on disaster risk reduction:

Words, deeds or institutions?

I thought it was worth highlighting since it provides a refreshingly honest appraisal of some academic work and standards. Twigg suggests that the authors and the journal should seek greater ambition and quality in the work they are producing and publishing respectively. 

How true does this hold for other journals and fields? It would be interesting to hear your thoughts….

Floods: Where Will the Water Lie?

My next few posts are going to be based around flooding. The posts will be interspersed with commentary around the current state of research, evidence of flooding through the Holocene, and what the future holds for human populations facing the flood hazard.

To kick things off here's a video of the destructiveness of floods when they are at their most severe. The Pakistan floods of 2010 were some of the worst in recent years. When you watch the video, start to think about what may cause such a set of events, how can we protect ourselves against the power of water, and what might the implications of anthropogenic climate change be?

Hurricanes and Climate Change

This post is intended to provide an overview of climate change and tropical cyclones. I’m going to start this post with some commentary to set the scene:

The detection and attribution of the possible effects of anthropogenic climate change on tropical cyclones is one of the most controversial topics in present-day science. The increase in tropical cyclone numbers in the Atlantic since the mid 1990s, combined with the devastating impacts of individual hurricanes such as Katrina in 2005, has let to an urgent examination of trends in the available tropical cyclone data to see if these can be explained by man’s effect on the climate.

Walsh et al (2009)

Observations through early October 2006 show that we have so far experienced an average Atlantic basin hurricane season. August had substantially below-average activity (only 45% of average) while September had above-average activity (about 140% of average). US landfall has been well below average. No hurricanes have made landfall along the US coastline this year. This has occurred in only 18 percent of the hurricane seasons since 1945. In an average year about 90 percent of the seasonal average NTC of 100 occurs by 11 October. 

Gray (2006)

El Niño years typically have the following tropical Atlantic conditions:

1.     stronger than normal 200 mb (~12 km) zonal winds (positive U),

2.     dryer middle tropospheric moisture conditions (negative q – specific humidity),

3.     somewhat higher than average sea level pressure anomalies (positive SLPA),

4.     somewhat higher than average sea surface temperature anomalies (positive SSTA).

Gray (2006)

Large amplitude fluctuations in the frequency and intensity of tropical cyclones greatly complicate both the detection of long-term trends and their attribution to rising levels of atmospheric greenhouse gases. Trend detection is further impeded by substantial limitations in the availability and quality of global historical records of tropical cyclones.

Knutson et al (2010)

But what is the situation now?

The IPCC (2013) provide a stark overview:

Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased.

Of critical importance for tropical cyclones:

Ocean warming dominates the increase in energy stored in the climate system, accounting for more than 90% of the energy accumulated between 1971 and 2010 (high confidence). It is virtually certain that the upper ocean (0−700 m) warmed from 1971 to 2010 (see Figure SPM.3), and it likely warmed between the 1870s and 1971.

And vitally:

Human influence on the climate system is clear. This is evident from the increasing greenhouse gas concentrations in the atmosphere, positive radiative forcing, observed warming, and understanding of the climate system.

So what does all this mean for the future of tropical cyclones?

The ambiguity of scientific literature investigating linkages between climate change and tropical cyclones is clear. Few papers agree on projected characteristics of storm systems in terms of their frequency and intensity. Much of the research suggests that regional changes will be of chief importance and as a result there is an absence of a generally agreed framework or theory regarding the impact of anthropogenic climate change on hurricanes.

If anthropogenic climate change causes an increase in hurricane activity, shouldn't we see positive trends over, say, the last 100 years? 

When accounting for missing data over that time period, statistical tests reveal that relative to the variability in the dataset, a correlation is not significantly distinguishable form zero. Hurricane numbers were high enough in the 1960s for a couple of decades that there is no significant positive trend from that period in time. Landfalling hurricanes even show a slight negative trend through time. More interesting, perhaps, is the apparent increase in the number of major hurricanes over this period - where major hurricanes are considered Category 4/5. However, the storms that do occur in the warmer climate simulation are more intense on average than those in the control (present day) simulation. 

The 'facts' are:

• Globally there has been no increase in tropical cyclone frequency over the past few decades (e.g. Webster et al, 2005; Elsner and Kocher, 2000).

• Storm frequency has not tracked recent tropical climate trends (Pielke Jr et al, 2005).

• The metrics of tropical cyclone intensity are varied and may be limited by data.

• While observations of tropical and subtropical sea surface temperature have shown an overall increase of about 0.2°C over the past ~50 years, there is only weak evidence of a systematic increase in potential intensity (Bister and Emanuel,2002; Free et al, 2004).

• Other authors suggest the intensity of Atlantic tropical cyclones is rising dramatically.

Elsner (2006) presents an interesting report on two competing hypotheses surrounding causes of increasing Atlantic hurricane activity. One hypothesis, known as the climate change hypothesis, suggests increases in greenhouse gases and their associated changes in eradicative forcing can cause SST in the Atlantic to rise through higher global temperatures. On the other hand, the Atlantic Multidecadal Oscillation (AMO) hypothesis suggests that natural ocean circulation changes in the Atlantic drive hurricane season SST, leading to changes in hurricane frequency and global temperatures. The common agenda in both competing theories is that regional SST is crucial in the genesis of tropical cyclones. The main discussion point is the interconnectivity between global temperatures and SST in the Atlantic. The jury is still out and the challenge remains to find the detailed causal mechanism between climatic change and tropical cyclone activity.

One of the most important pieces of research on the subject has come from Knutson et al (2008) in their letter to Nature. The authors present the results of a study investigating the changes in large-scale climate through the 21^st century using an ensemble of global climate models and describe that Atlantic hurricane frequencies reduce. The results ‘do not support the notion of large increasing trends in either tropical storm or hurricane frequency driven by increases in atmospheric greenhouse-gas concentrations’.

Monster Cyclone Haiyan

Following on from my post about tropical cyclones in the 'Past, Present and Future', I am now going to discuss the recent cyclone Haiyan in the Philippines. One month after Haiyan, the death toll stands at 5,924 and 1,779 people are still missing as per government figures released last Sunday.

'Galvanised iron sheets were flying just like kites' 

(Mai Zamora from World Vision).

Haiyan was one of the strongest typhoons ever to hit land with winds of up to 320 km/h (BBC News). Sustained wind speeds of that extent are what we would expect of a category five hurricane. These winds caused waves as high as 15 metres and up to 400mm of rain in some places. These extreme conditions caused destruction that was extensive and devastating.

Figure 1: Satellite image as Haiyan approached the Philippines

In terms of the damage to infrastructure, the storm caused widespread damage. Reports of building being ripped apart, flash floods and landslides were rampant. The country was in a state of chaos whereby schools and offices were closed, flights were suspended and soldiers were entrusted with rescue and relief operations. Furthermore, the storm meant that power and communication lines were cut to some areas.

Haiyan affected millions of people, 12 million according to officials. Even the capital felt the force of the storm despite being far away from the eye of the storm, however other cities weren't as fortunate. Raging across Leyte and Samar, it turned roads into rivers and left Cebu city devastated, home to over 2.5 million people. The black arrow in figure 2 indicates the path of the storm. It suggests that the storm passed through some of the most densely populated parts of the Philippines therefore affecting an extensive proportion of the population. 

Figure 2: population density of the Philippines

The Philippines has experienced numerous super typhoons over the past decades. Haiyan was the 25th to enter the territory this year. Scattered along the worlds most active typhoon belt, there are plentiful supplies of warm water and moist air to provide the energy to kick start super storms. Despite these factors concerning the formation of a cyclone, Haiyan has shown a number of unusual features. 

As explored in my previous post, the walls of the storm that normally rotate around the eyes are replaced as it moves, often weakening the wind speed. In the case of Haiyan, this didn't happen. Further to this, the upwelling of cold water which would usually serve to reduce the energy of a storm did not take place as Haiyan was travelling so quickly. These two factors meant that Haiyan was unique in nature. 

Figure 3: typhoon Haiyan relief effort

In a blog post by Jeff Masters, the damage is described as 'perhaps the greatest wind damage any city on Earth has endured from a tropical cyclone in the past century'. Figure 3 gives just a snap shot of the damage. 

The question is: will this trend of monster cyclones gain momentum in the future? Does anthropogenic climate change have a role in the increasing frequency and severity of so called 'natural' disasters? Find out more on hurricanes through the Anthropocene next time. 

World’s Worst Earthquakes Caused By Man

This short article in the Sunday times caught my attention whilst I was reading about current trending stories about Nelson Mandela and Nigella Lawson. 'Scientists have suggested some of the worlds largest and most deadly recent earthquakes were not natural disasters at all - but were instead caused by human activities' (Jonathan Leake, Science Editor). To read the whole article click here.

Figure 1: The Sichuan earthquake in China

The article has emerged following findings from a global study of hundreds of earthquakes by Klose whose research in the Journal of Seismology identified 92 large earthquakes which could be linked to human impact. He published a paper in 2010 titled 'Human-Triggered Earthquakes and Their Impacts on Human Security' which is also worth looking at. 

This is extremely interesting and relevant. So far in my blog, I have looked at the science of different individual natural hazards and the characteristics of our world population in terms of size and location. In the next few weeks I will begin to draw links between hazards and population. This article is perfect to get the ball rolling.