October 24, 2007

scientists comment on California wildfires

Wildfires have decimated large areas of California for several days and continue to spread.

Martin Wooster, Professor of Earth Observational Science, based at King’s College London, said:

“Wildfires have been occurring naturally for millions of years. In many cases they have positive ecological effects, such as the promotion of new vegetation re-growth.

“In California, forest fires mostly occur between September and December. This is when hot, dry and rapid ‘Santa Ana’ and ‘Diablo’ winds are more common. These winds are highly conducive to the rapid spread of fire.

“More people than ever before are now living closer to the areas where, in previous years, wildfires would not have affected them. This is obviously having a huge impact on the communities living in these areas.

“Wildfires are sometimes ignited by natural phenomena, such as lightening, but most these days are lit by humans, deliberately or otherwise.

“As we’ve seen in California, under particular meteorological conditions and with sufficient ‘vegetation fuel’, fires spread rapidly. They can become very difficult to control, even with the substantial resources of information, manpower and equipment available to modern fire-crews.

“It is also fair to say that the effects of climate change on fire also cannot be discounted. In the same way that it impacts patterns of rainfall, temperature and even wind, changes in the climate also influence patterns and magnitudes of fire. In California, scientists have recently suggested that future climate change may lead to an increase in ‘Santa Ana’ winds during the ‘fire season’, and this could in turn lead to more frequent or even to more devastating fires.

“Fire management strategies that take into account the competing needs of the natural environment and the human population are required in order to lessen the impact of fires in these areas.”

Professor Brian Hoskins, Walker Institute for Climate System Research, University of Reading, said:

“There is high pressure sitting over the Mojave Dessert and this has been there for a while. The coast of California is largely protected from the hot, dry dessert air by mountains that are generally 1-2km high. Most of coastal California has not been getting strong winds, but where there are passes in the mountain ranges the air rushes over them from the high pressure inland causing the localised very strong winds. As this air descends to sea level it becomes even drier and hotter. There is a long-term drought in the South-West US and so the ground and the vegetation are very dry. This means that the strong, hot, dry winds are very likely to lead to fires. The air flowing over and between mountains tends to change its direction quickly and irregularly so that the spread of the fire is not very predictable.”

Dr Peter Thomas, Fire Ecology Expert, Keele University, said:

“Fires in this area of California are normal occurrences, but what makes this set of fires so much of a problem is the unusually high speed of the Santa Ana winds. These hot, dry winds – sometimes called the Devil’s Breath – occur every autumn/winter, normally blowing at around 30 mph but this year they’re reaching gusts of over 100 mph.

“The hot dry conditions dry out living and dead vegetation making it very flammable. When a fire starts, the high wind speeds accelerate 1) the spread of the fire and 2) make it more intense. It does this mainly by bending the flames towards the ground, preheating the fuel so it ignites quicker. Under the right conditions whole hill sides can ignite almost instantaneously. The high winds can also carry this preheating from almost horizontal flames across fire breaks – as is being seen in California, jumping 10 lane highways. Worse still, the high winds carry burning embers up and ahead, starting new ‘spot fires’. These create their own hazard as the wind quickly makes them into big fires, but they can also trap fire-fighters and those fleeing their homes as they find fire ahead and now suddenly also behind them. The rising convection column of hot air from the original and the spot fires can also draw the fires together at devastating speed, accelerating that caused by the wind.

“The real problem with these fires is not so much the ecological damage – fires after all have been burning here for thousands of years – but their speed and unstopability. Despite tremendous fire fighting technology and highly skilled fire-fighters, the only thing that will stop these fires is a change in the weather.”

Professor Ian Colebeck, Director, Centre of Environment and Society, University of Essex, said:

“As a result of the smoke from the wildfire levels of air pollution in areas of California have been classified as very unhealthy by the US Environmental Protection Agency. The pollution is particularly hazardous and the elderly and people with heart and/or lung diseases are particularly at risk to the harmful effects from type of pollution exposure. In fact there has been a dramatic increase in the number of people going to hospitals with respiratory problems.

“The fires have produced vast quantities of soot and ash, raising the particulate level to six times the norm.”

Professor Jonathan Grigg, Professor of Paediatric Respiratory and Environmental Medicine at Queen Mary’s School of Medicine and Dentistry, said:

“The wildfires in the US are a threat to health. Fires of this scale produce large amounts of inhalable carbon particles, and noxious gases. Individuals most at risk are the elderly, children, and those with lung conditions such as asthma, and chronic bronchitis. The effect of the 2003 Southern Californian Wildfires on children’s health has been studied – and were reported last year (Kunzli and colleagues, American Journal of Respiratory and Critical Care Medicine 2006). This research found that the number of smoky days was associated with increased wheezing, attacks of asthma, cough, bronchitis, and visits to a doctor. They also found evidence that individuals that took preventative action (e.g. wearing masks, and staying indoors) had less adverse health effects. Similar findings have been seen in adults exposed to bushfire smoke in Australia – where increased levels of smoke particles were associated with increased hospital admissions for respiratory conditions (Johnston and colleagues BMC public health 2007).”

Professor John Dold, Chair of Applied Mathematics at the University of Manchester, said:

“Strong winds can greatly intensify wildfires, making them harder to extinguish and indeed harder to escape from. The wind can also carry burning embers, causing new fires to spring up some distance away.

“Firefighters need to be constantly on the lookout for these ‘spot fires’, which can quickly develop into major infernos and are the main way in which wildfires spread into urban areas. If not put out at an early stage, a wind-driven fire can grow to overwhelm whatever resources are available for extinguishing the flames. In this situation firefighters are restricted to vital damage-limitation work, until weather conditions change or the vegetation is burnt out. This outcome is more likely if vegetation is initially dry and plentiful, which will be more common if the current trend towards wet fertile winters followed by drier summers in some parts of the world continues.

“Unlike house fires, in which the oxygen supply is often limited, carbon monoxide poisoning is not usually a problem with wildfires. However, wildfires release many potentially toxic compounds from the flames and from the breakdown of vegetation, which are particularly dangerous for people with breathing difficulties such as asthma. Very large fires can also release a lot of greenhouse gases that are not recaptured until the vegetation regrows, sometimes decades down the line.”

Dr Kelly Berube, Lecturer in Cell Biology, Cardiff University , said:

“Inhalation of combustion-derived particles in urban air causes increased illness and death in persons with pre-exsiting lung and heart conditions; bush-fire particles will add further insult to lung and heart injury.”

Dr. Clifford Jones, Reader in the Department of Engineering at the University of Aberdeen, said:

“Wind accelerates the propagation of forest fires very powerfully, and makes them more difficult and dangerous to control. It is possible that the unusually strong winds we are observing at the moment are linked to El Nino, which is monitored by the Californian fire agency. Forest fires have a strong impact on air quality, producing abundant smoke that is likely to be quite acrid. They also release nitrous oxide, a powerful greenhouse gas, and increase the levels of polyaromatic hydrocarbons in the atmosphere. Most worryingly for human health, forest fires often release highly toxic dioxin in quantities that, though miniscule, can cause serious problems. There are also dangers to the environment over and above the loss of vegetation. If the nutrient-rich top layer of the forest floor is destroyed, soil quality will fall. It also remains to be seen whether the foam used to fight the fires will enter rivers, potentially altering pH and affecting freshwater life. However, once contaminants have dispersed, the forest should revive naturally. Such re-growth can however take a very long time. The damage to vegetation resulting from the bush fires in Greece earlier this year is expected to take 20 years to repair itself.”