Why do natural disasters occur? Part 3

How hot are you? I don't mean aesthetic-wise, but rather temperature-wise. Your body temperature should be in the range of 36.5 - 37.5°C (97.7 - 99.5 °F), which is quite warm but it's not hot. Let's turn up the heat.

Where is the hottest place on Earth?

https://en.wikipedia.org/wiki/Extremes_on_Earth

https://en.wikipedia.org/wiki/Death_Valley

• If you chose Death Valley as your final answer, you would be correct. This barren desert valley is located in Eastern California, in the northern Mojave Desert, which borders the Great Basin Desert. 
• If you thought no one ever lives in this location, you would be wrong. It is home to the Timbisha tribe of native Americans, formerly known as the Panamint Shoshone, who inhabited the valley for at least 2 millennia. The name Timbisha derives from the word tümpisa meaning 'rock paint', which refers to red ochre paint made from the clay found in the valley. 
• The name 'Death Valley' was coined in 1849 by prospectors and others during the California Gold Rush who sought to cross the valley on their journey to the gold fields. During the journey, 13 pioneers perished from an early expedition of wagon trains. 

Describe the ecology of Death Valley 

• If you thought weather conditions here are unsuitable for flora to thrive here, you would be wrong. Explorers discovered a number of flowers species watered by snowmelt blooming in spring. 
• If you thought no wildlife could survive in these weather conditions, you would be wrong. A number of animal species have be discovered to roam this valley, such as the bighorn sheep, red-tailed hawks, and wild burros. 
• Moreover, there are over 600 springs and ponds (e.g. Salt Creek) that are home to pupfish populations, which are remnants of the wetter Pleistocene climate. 
• Kettmann et al. (2008) discovered over 80 species of birds around a large pond surrounded by willows and cottonwood trees adjacent to a 30 m (100 ft) high Darwin Falls, on the western edge of Death Valley Monument. 

https://www.oasisatdeathvalley.com/plan/wildflowers/

Describe the geology of Death Valley 

This map illustrates the system of once-interconnected Pleistocene lakes in eastern California (USGS). 

• It is described as a graben, which is a down-dropped block of land between 2 mountain ranges. 
• It is located at the southern end of a geological trough, Walker Lane, which extends north to Oregon. 
• The valley is bisected by a right lateral strike slip fault system, which consists of the Death Valley Fault and the Furnace Creek Fault. 
• The eastern end of the left lateral Garlock Fault intersects the Death Valley Fault. Meanwhile, the Furnace Creek and the Amargosa River flow through part of the valley and submerge into the sands of the valley floor. 
• A 2009 geological consensus stated that around 10,000-12,000 years ago (middle of the Pleistocene era), an inland lake called "Lake Manly" formed in Death Valley. This lake is roughly 160 km (100 mi) long and 180 m (600 ft) deep, with the end-basin beginning at Mono Lake in the north. Then it streams through basins down the Owen River Valley, through Searles and China Lakes and the Panamint Valley, in the west. 
• As the region transformed into a desert, the water evaporated, it left an abundance of evaporitic salts, such as common sodium salts and borax. 

Describe the climate in Death Valley 

Climate data for Death Valley (Furnace Creek Station) 

Source: NOAA 1981-2010 US Climate Normals

• It is well-known that Death Valley is home to a subtropical, hot desert climate with prolonged hot summers and short, mild winters, and little rainfall. 
• Since it lies in the rain shadow of 4 major mountain ranges (including the Sierra Nevada and Panamint Range), it is one of the driest locations in the world. 
• For moisture to approach Death Valley, it has to drift inland from the Pacific Ocean and pass eastward over the mountains. As air masses are driven upwards by each range, they cool and moisture condenses, and fall as rain or snow on the western slopes. 
• Roof & Callagan (2003) found that a large portion of the air masses reaching Death Valley would disintegrate, leaving scarce moisture to fall as precipitation. 

A number of factors have been identified that contribute to the extreme heat of Death Valley: 

-- Solar heating = Since the air is clear and dry, the land is black and vegetation is sparse, the valley's surface experiences intense solar heating especially in the summer months. 

-- Trapping of warm air = The warm air in Death Valley is continually reheated since it is trapped by high, steep valley walls and recirculated back to the valley floor. 

-- Migration of warm air from other areas (advection) = The air tends to be heated over warmer desert regions adjacent to Death Valley prior to its arrival in the valley. 

-- Warm mountain winds = As winds are driven upwards and over the mountains, they are heated to become 'foehn winds'. 

• A 2008 study found severe heat and dryness are contributing factors to perennial drought-like conditions in Death Valley, which limits the development of clouds from passing through the valley, where precipitation exists as a virga. 
• Since Death Valley is an elongated and narrow gorge that descends below sea level and is barricaded by high, steep mountain ranges, with sparse flora, it heats the desert surface towards scorching temperatures. A 2009 study measured the overnight lows during summer months range between 28 and 37^oC (82 to 89^oF). 
• The hottest air temperature ever recorded in Death Valley (and on Earth) was 56.7 °C (134°F) on 10th July 1913 at Furnace Creek (formerly Greenland Ranch). It occurred during a heat wave that featured 5 consecutive days above 54 °C (129.2 °F).
• The hottest surface temperature recorded in Death Valley (and on Earth) was 93.9 °C (201 °F) at Furnace Creek on 15th July, 1972.
• The longest streak of days with a maximum temperature of at least 38 °C (100 °F) was 154, during the summer of 2001, in Death Valley.
• The highest overnight or low temperature recorded in Death Valley was 42 °C (107 °F), on 12th July, 2012. Moreover, on the same day, the mean 24-hour temperature recorded at Death Valley was 47.5 °C (117.5 °F).

If you think it never rains in Death Valley all year, then you would be surprised that flooding events actually occurs in this region. 

• Between 1931 and 1934, only 16 mm (0.64 inches) of rain was recorded over a 40-month period, which was the driest period. 
• In 2009, the WRCC evaluated the average annual precipitation in Death Valley is 60 mm (2.36 inches), while Greenland Ranch station recorded an average 40 mm (1.58 inches). 
• On January 1995, 66 mm (2.59 inches) of rain fell on Death Valley, making it the wettest month on record. Moreover, between mid-2004 and mid-2005, an estimated 150 mm (6 inches) of rain poured over Death Valley, making it the wettest period on record. This formed ephemeral lakes in the valley and produced vast wildflower blooms. 

A Landsat 5 satellite photo of Lake Badwater shot on February 9, 2005

A Landsat 5 satellite photo of Badwater Basin dry lake shot on February 15, 2007

When do you think Earth is physically closest to the Sun? 

• If you live in the Northern Hemisphere, you would think it is between June and August, the summer months in that hemisphere. Conversely, if you live in the Southern Hemisphere, you would think it is between December and February, the summer months in that hemisphere. 
• Because of Earth's elliptical orbit around the Sun, there is one portion closest to the Sun and one portion farthest away from the Sun. 
• The portion closest to the Sun is called the "perihelion", and the portion farthest away from the Sun is called the "aphelion". 

• The perihelion occurs around January 1st - 5th, which is 2 weeks after the December Solstice. During this time, the Earth is approximately 147.3 million km from the Sun. 
• The aphelion occurs around July 1st - 5th, which is 2 weeks after the June Solstice. During this time, the Earth is approximately 152.1 million km from the Sun. 
• Logically, all of Earth should be considerably warmer during December, January and February, yet the weather data tell a different story statistically. Why is this the case? What other factors haven't we considered? We need to understand about the relationship between the Sun and the Earth. 

https://en.wikipedia.org/wiki/Summer

https://en.wikipedia.org/wiki/Summer_solstice

https://en.wikipedia.org/wiki/Daytime

What is daytime? 

• When a given location is naturally illuminated by direct light from the Sun for a period of time of the day, it is referred to as 'daytime'. This occurs when the Sun appears above your local horizon anywhere on the globe's hemisphere facing the Sun. 
• Approximately 50% of the Earth is illuminated by the Sun at any time, but the proportion of additional illumination could vary due to indirect atmospheric effects. 
• When one hemisphere experiences daytime at any given instant, it changes continuously as Earth rotates on its own axis. 
• Since Earth's axis is not perpendicular to the point of its orbit around the Sun, the length of the daytime period varies from one position on Earth to another. 
• Because the axis of rotation is relatively fixed compared to the stars, Earth moves relative to the Sun during its orbit around it. This leads to seasonal variations in the length of the daytime period on a large proportion of points on Earth's surface. 
• From your perspective, the period of daytime is estimated as the period between sunrise and sunset. Since the Sun is a luminous disc according to an Earth observer, sunrise and sunset are instantaneous and their definitions vary with context. 
• Note that the Earth's atmosphere further diverts and diffuses light from the Sun and extends the period of sunrise and sunset. When sunlight indirectly illuminates the Earth's sky for a period after sunset and before sunrise, it is referred to as 'twilight'. 

How do daytime periods vary with latitude and season? 

This graph illustrates the day length as a function of latitude and the day of the year. Latitude 40^o N (roughly New York City, Madrid and Beijing) is highlighted as an example.

• Earth's axis of rotation is tilted 23.44^o to the line perpendicular to its orbital plane, known as the ecliptic. Depending on your latitude, the length of daytime varies with the seasons on Earth's surface. 
• Regions tilted towards the Sun experience more than 12 hours a day in daylight and warmer temperatures, because of the greater directness of the solar rays and lower absorption of sunlight in the atmosphere.
• There is a misconception that warmer temperatures are a result from the increased periods of daylight, when in fact it is the Sun's rays direct illumination on the Earth's surface. 
• The higher angles (around the zenith) of the Sun contributes to the warmer temperatures of the tropics, while lower angles (just above the horizon) contributes to the lower temperatures of the polar regions. 
• Despite experiencing 24 hours of daylight a day for 6 months, the poles are significantly cold during their respective summers. On the other hand, the Equator experiences only 12 hours of daylight a day and it remains relatively warm throughout the year. 

i. At the Equator 

• Observers from the equator view the Sun rising and setting vertically, following an apparent path almost perpendicular to the horizon. Because of Earth's axial tilt, the Sun always situates within 23.44^o north or south of the celestial equator, hence the subsolar point always situates within the tropics. 
• From the March equinox to the September equinox, the Sun ascends within 23.44^o north of due east, and situates within 23.44^o north of due west. 
• From the September equinox to the March equinox, the Sun ascends within 23.44^o south of due east and situates within 23.44^o south of due west. 
• The Sun's trajectory situates solely in the northern half of the celestial sphere from the March equinox to the September equinox, but situates solely in the southern half of the celestial sphere from the September equinox to the March equinox. On the equinoxes, the equatorial Sun terminates at the zenith, which passes directly overhead at solar noon. 
• Since the equatorial Sun is the closest to the zenith at solar noon, the tropical zone contains the warmest areas on Earth overall. 
• Since the Sun's trajectory across the sky is virtually perpendicular to the horizon, the Equator experiences the shortest sunrise or sunset. 

ii. In the tropics 

• The tropics occupy a zone between the latitudes 23.44^o north and 23.44^o south of the Equator. Within this zone, the Sun passes more or less directly overhead on at least 1 day per year. 
• The latitude of 23.44^o north is called the Tropic of Cancer, since the Sun passes overhead at this location at a certain time of the year when it is close to the constellation of Cancer. 
• The latitude of 23.44^o south is called the Tropic of Capricorn, for similar reasons. 
• It is known the sun enters and leaves each zodiacal constellation later each year at a rate of 1 day every 72 years. 
• The Sun is directly overhead only once per year on the Tropical Circles, on the corresponding solstice. At latitudes adjacent to the Equator and on the Equator itself, the sun will be overhead twice a year. However outside the tropics, the Sun never passes directly overhead. 

Earth daylight on the June solstice

Earth daylight on the December solstice

iii. Around the poles 

• The seasonal variations in the length of daytime are substantial around the poles, which coincide with the Earth's rotational axis as it passes through the surface. 
• Within 23.44^o latitude of the poles, there are some days per year when the sun never falls below the horizon, as well as above the horizon. 
• Northern locations that experience 24 hours of summer daylight is known as the 'midnight sun'. 
• When the sun is less than 6 degrees below the horizon, the sky is relatively illuminated and the stars can't be observed. This means 24-hour nights with stars visible all the time only occur beyong 72 degrees north or south latitude. 
• At or near the poles, the Sun never rises highly above the horizon, even in the summer, which attributes to the consistent cold temperatures all year around. 
• As you approach the poles, the Sun's apparent path through the Earth sky each day gradually diverges away from the vertical. 
• As summer approaches, the sunrises and sunsets is more northerly in the north pole and more southerly in the south pole. 
• At the poles, the Sun's path is circular, which is approximately equidistant above the horizon for the whole duration of the daytime period on any given day.
• As winter approaches, the sun's circular path falls below the horizon and vice versa as summer approaches. 

iv. At middle latitudes 

• The variations in the length of daytime are modest at the middle latitudes. In the higher middle latitudes (Montreal, Paris and Ushuaia), the difference between summer and winter daytime lengths are discernible. For instance, the sky may be illuminated until 9 pm during the summer, but until 5 pm during the winter. 
• In the lower middle latitudes (Southern California, Egypt and South Africa), the seasonal differences are smaller, with approximately 4 hours difference in daytime length between the winter and summer solstices. 
• Using the rule of 12ths, the increase in the daytime length from winter to summer can be calculated. 

1st month: 4*(1/12 * 60) = 20 mins 

2nd month: 4*(2/12 * 60) = 40 mins 

3rd month: 4*(3/12 * 60) = 60 mins

v. Variations in solar noon 

• When the Sun approaches its highest point in the sky, it creates a solar noon with seasonal variations such as the 'equation of time'. 

Natural disasters associated with tremendously high temperatures and scorching hot air tend to occur during the summer months and in the daytime, which are heat waves, droughts, and wildfires. I'll be discussing each of them in detail. 

vi. Heat Waves 

https://en.wikipedia.org/wiki/Heat_wave

https://en.wikipedia.org/wiki/List_of_heat_waves

• Heat waves are defined as periods of sweltering weather, which may be accompanied by high humidity, particularly in oceanic climate countries. However, the specificities of the definition vary from country to country, which may be confusing. 
• Frich et al.'s Heat Wave Duration Index defined a heat wave as "the daily maximum temperature of more than 5 consecutive days exceeding the average maximum temperature by 5 ^oC (9 ^oF)". 

How do heat waves form? 

• When high pressure aloft (3,000 - 7,600 metres or 10,000 - 25,000 ft) intensifies and situates over a region for several days up to several weeks, it creates heat waves.
• Since the upper level high pressure moves slower during summer, the air subsides towards the surface, where it warms and dries adiabatically, inhibits convection and blocks the formation of clouds.This, in turn, increases the amount of short-wave radiation reaching Earth's surface. 
• The presence of a low pressure system at Earth's surface causes surface wind from lower latitudes to carry warmer air, manifesting in greater warming. 
• Lau & Nath (2012) suggested other causes of heat waves such as the surface winds sweeping from the hot continental interior towards the coastal zone, and a transition of warm air from high to low altitudes, augmenting subsidence and thus adiabatic warming. 

What are the health effects of heat waves? 

https://en.wikipedia.org/wiki/Heat_index

                                         NOAA national weather service: heat index 

Heat index is a measure of how hot it feels when relative humidity is factored with the actual air temperature.

• 26-32 ^oC = Caution - Fatigue is possible with prolonged exposure and activity. If activity continues, it manifests in heat cramps.
• 32-41 ^oC = Extreme caution - Heat cramps and heat exhaustion can occur. If activity continues, it manifests in heat stroke. 
• 41-54 ^oC = Danger - Heat cramps and heat exhaustion are likely to occur. Heat stroke is probable if activity continues. 
• 54+ ^oC = Extreme - Heat stroke is imminent. 

a. Hyperthermia (Heat stroke) 

• This increases the risk of heat-related illnesses in older adults, young children and those who are physically ill or overweight. Doctors recommend taking prescription medications such as diuretics, anticholinergics, antipsychotics, and anti-hypertensives, to treat symptoms. 

b. Heat oedema 

• This involves transient swelling of the hands, feet, and ankles, and is secondary to increased aldosterone secretion, which promotes water retention. 
• Combined with peripheral vasodilation and venous stasis, excess fluid accumulates in the dependent areas of extremities, resulting in oedema. 
• Although heat oedema usually disappears treatment-free after a few days when the patient acclimatises to the warmer environment, it is recommended to wear support stockings and lift the affected legs in order to minimise the oedema. 

c. Heat rash

• Also known as prickly rash, this condition is a maculopapular rash accompanied by acute inflammation and occluded sweat ducts. This dilates and ruptures sweat ducts, which results in small pruritic vesicles on an erythematous base. 
• If heat rashes continue for a period of time, it manifests in chronic dermatitis or a secondary bacterial infection. 
• Doctors recommend those suffering from heat rash to wear loose-fitting clothing instead of tight clothing. Moreover, the treatments they recommend include chlorhexidine lotion to eliminate any desquamated skin, anti-histamines for itching, and antibiotics for infection. 

d. Heat cramps 

• They are painful, severe, involuntary spasms of the large muscle groups utilised in intense physical exercise. This usually occurs in people exercising strenuously as well as sweating profusely and replenishing fluid loss with water containing non-electrolytes. This manifests in hyponatremia, thus cramping in fatigued muscles. 
• Doctors recommend fluids containing salts or electrolytes for rehydration in order to achieve relief. 

e. Heat syncope 

• When one is exposed to excessive heat, it results in orthostatic hypotension, which manifests in a near syncopic episode. Researchers suggest heat syncope is associated with profuse sweating, leading to dehydration, and thereby peripheral vasodilation and decreased venous blood return in spite of decreased vasomotor control. 
• Treatment of heat syncope include cooling and rehydration by oral rehydration therapy (electrolyte drinks) or isotonic IV fluids. 
• Other recommendations include standing in cooler areas, and wearing support stockings and engaging in knee-bending movements. 

f. Heat exhaustion 

• This condition is similar to heat stroke with the difference being the person's neurologic function spared. 
• Symptoms of heat exhaustion include extreme dehydration, electrolyte depletion, diarrhoea, dizziness, headache, malaise, myalgia, nausea, tachycardia and vomiting. 
• Recommended therapies include escaping the heat and rehydration with fluids such as IV isotonic fluids. 

How are heat waves deadly? 

• According to the World Health Organisation, more than 166,000 people have died due to heatwaves between 1998 and 2007, including more than 70,000 fatalities during the 2003 Western European heatwave affecting mainly France, England and Spain. 
• They also found the number of people exposed to the effects of heat waves have increased by approximately 125 million between 2000 and 2016, which continues to increase due to climate change. 
• WHO projects an additional 250,000 deaths per year attributing to climate-sensitive diseases from 2030 onward. 
• Compared to average years, the most amount of people exposed to heat waves worldwide in a single year with 175 million occurred in 2015. 
• The number of heat fatalities is likely underreported due to a lack of reports and misreports. This is partly due to the "harvesting effect", which is a term for a 'short-term forward mortality displacement'. This refers to the compensatory reduction in mortality during the subsequent period after a heat wave. 
• Huynen et al. (2001) thought this finding indicates heat impacts those who are extremely ill to the point "they would have died in the short term". 
• Another suggestion of the underreporting is the social attenuation in contexts of heat waves as a health risk. Based on the effects of the 2003 French heat wave, Poumadère et al. (2005) thought the heat wave impacts manifest from the association of natural and social factors. 

Notable historical heat waves include: 

- 1757 July in Europe 

- 1896 Eastern North America = Killed about 1,500 people 

- 1900 Argentina heat wave impacting mainly Buenos Aires and Rosario 

- 1901 Eastern United States = Killed 9,500 people 

- 1906 United Kingdom

- 1911 Eastern North America = Killed between 380 and 2,000 people 

- 1911 United Kingdom 

- 1936 North America during the Dust Bowl

- 1950s Central & Southern United States 

- 1960 Oodnadatta, South Australia = The highest recorded temperature in the Southern Hemisphere and Oceania, which is 50.7 ^oC (123.3 ^oF). 

- 1972 New York & Northeastern United States = Approximately 900 people died 

- 1980 United States, particularly central and eastern regions such as Kansas City, Missouri, Dallas / Fort Worth and Wichita Falls, Texas = Around 1,000 people died. 

- 1983 United States = Impacted states include Iowa, Illinois, Michigan, Missouri, Indiana, Wisconsin, Ohio, Minnesota, Kansas, Nebraska, and Kentucky 

- 1987 Greece = More than 1,000 died in Athens 

- 1988 United States = Between 5,000 and 10,000 people died 

- 1995 United States particularly Chicago, Illinois and Wisconsin = At least 778 deaths, most of them were African American Chicagoans 

- 2006 Europe impacted Benelux Union, Germany, and Great Britain 

- 2006 North America (USA and Canada) = Around 220 died 

- 2009 Australia = Regions impacted include Adelaide, South Australia, and Kyancutta and Melbourne, Victoria 

- 2009 Argentina in regions of Buenos Aires and Santa Fe 

Frequency of occurrence (vertical axis) of local June-July-August temperature anomalies (relative to 1951-1980 mean) for Northern Hemisphere land in units of local standard deviation (horizontal axis). Temperature anomalies in the period 1951-1980 closely fit under the normal distribution (green), which defines the cold (blue), typical (white) and hot (red) seasons, each with probability of 33.3%. The distribution of anomalies has shifted to the right due to global warming of the past 30 years.

a. 2010 

• Northern Hemisphere summer heat wave affecting regions such as Northeastern China and European Russia. 
• June Eastern European heat wave impacting mainly Bulgaria with heat originating from the Sahara Desert. 
• 4-9 July American East Coast affecting states such as the Carolinas, Maine, Pennsylvania, New York, Maryland, District of Columbia, Delaware, New Jersey and Massachusetts. 

b. 2011 

• Late July and early August Southwestern Asian heat wave affecting countries such as Iraq, Georgia and parts of the Middle East. 
• North American heat wave affecting mainly Midwestern USA, Eastern Canada and a proportion of the Eastern Seaboard 

c. 2012 

• Late June to mid-August North American heat wave affecting the Rocky Mountains.

d. 2013 

• Angry Summer or Extreme Summer of Australia from December 28 to January 9. It broke 123 weather records, including the hottest day ever recorded in Australia, hottest January, hottest summer average, and an entire week above 39 °C (102 °F).
• Southwestern United States, esp. Southern California and Death Valley when temperatures reached and exceeded 50 °C (122 °F) respectively.
• Canada Day heat wave impacted Southwestern United States and southern British Columbia, Washington and Oregon.
• July - August China heat wave affecting the following regions: Zhejiang, Chongqing, Shanghai, Hunan, Xinchang, Zhejiang, Changsha, Hunan and Hangzhou.
• December 11, 2013 to January 2, 2014 Argentina heat wave = The longest Argentinian heat wave since records began in 1906.

e. 2015 

• April - May India heat wave: Killed more than 2200 people, especially in Andhra Pradesh and Telangana.
• 30th June - 5th July & late June - mid-September: The Western European heat wave was caused by a Spanish plume, which raised temperatures in countries from Morocco to England. Di Liberto (2015) reported record heat waves in the Maghreb Mediterranean coast, south-western, central and south-eastern Europe.

f. 2016 (Warmest year on record)

• June American heat wave affecting the states of California, Arizona and Nevada.
• July Kuwait heat wave reaching temperatures of 54 °C (129 °F), the highest temperatures ever recorded in the Eastern Hemisphere and anywhere outside Death Valley.
• April-May Indian heat wave recording 51 °C (123.8 °F) in Rajasthan. Over 160 people died and over 330 million people were impacted.

g. 2017 

• January 25-27 Chilean heat wave that concentrates on the Metropolitan Region of Santiago and La Araucania Region.
• 28th June Iranian heat wave affecting the cities of Jask and Ahvaz
• July Chinese heat wave affecting the following locations: Chongqing, Xi'an, Hangzhou, Hefei, Shanghai (Xujiahui Station), Nanjing, Wuhan, Shaanxi and Turpan.

h. 2018 

• May-June Pakistan & Indian heat wave that killed at least 65 people.
• April British Isles heat wave
• Late May North American heat wave affecting mainly Mexico
• Mid-July Japanese heat wave causing over 22,000 hospitalisations and 80 deaths.

i. 2019 

• December Australian heat wave: New South Wales recorded its warmest January since 2011 and Adelaide, South Australia recorded its hottest day on 24th January since 1939. Furthermore, Melbourne, Victoria recorded its hottest day on 25th January since the 2009 Black Saturday Bushfires.
• Mid-May to mid-June Indo-Pakistani heat wave reached temperatures of 50.8 °C (123.4 °F) in Churu, Rajasthan.
• June-July European heat wave due to hot air that drifted from Sahara desert over to Europe affecting countries such as France, Germany, UK, Belgium and Luxembourg.
• 17th December Australian heat wave that exacerbated the 2019-2020 Australia bushfire season

j. 2020 

• May 27th heat wave impacting Northern New England and Eastern Canada with places such as Ottawa & Burlington, Vermont, and Caribou, Maine, as well as Montreal, New Brunswick, and Quebec.
• June 20th Siberian heat wave that broke the record for the hottest temperature in Verkhoyansk, Russia, which was 38 °C (100 °F).

What are other effects of heat waves? 

A. Psychological and sociological effects 

• The psychological stress imposed by heat waves can hinder performance, as well as increase crime rates. Simister & Cooper (2004) discovered a correlation between high temperatures and both interpersonal and societal conflict, as well as the incidence of violent crimes such as assault, murder, and rape. 
• Hsiang et al. (2015) found politically unstable countries that experience civil wars correspond with high temperatures. Hsiang & Deryugina (2014) also found significant correlations between high temperatures and income, as well as economic productivity. Their model suggested for each degree Celsius above 15^oC (59  ^oF) individuals day of economic productivity decreases by about 1.7%. 

B. Power Outages 

• Hot summer days associate with elevated electrical demand due to high usage of air-conditioners and fans during the daytime and nighttime. This increases the risk of power outages, leading to widespread blackouts. 
• Examples of power outages associated with heat waves include the 2006 California heat wave, and 2009 South Eastern Australian heat wave. 

C. Wildfires 

• When heat waves coincide with drought, drying out vegetation in the affected regions, it increases the risk of bushfires and wildfires. 
• For example, the 2003 European heat wave sparked a wildfire that destroyed over 3,010 sq km (1,160 sq km) or 301,000 ha (740,000 acres) of forest and 440 sq km (170 sq mi) or 44,000 ha (110,000 acres) of agricultural land, with an estimated damage cost of over 1 billion euros. 

D. Physical damage 

The physical damage heat waves can exert include: 

• Buckling and melting roads and highways 
• Bursting water lines 
• Detonating power transformers -> Fires 
• Buckling and kinking rail lines -> Delaying rail traffic, cancelling services 

There are concerns from scientists that there is an increasing likelihood and severity of heat waves occurring in both the short-term and long-term future. A majority of society affected by heat waves will be inside non-air-conditioned confined spaces, where the indoors temperatures are sweltering. There are calls from experts for current buildings to be redesigned and future buildings to be constructed in a way to mediate the internal climate relative to the external climate. In addition, there are proposals for educating world society about the climate issues and its impacts on society, as well as individuals. 

I'll discuss climate change and global warming in another post. 

vii. Droughts 

https://en.wikipedia.org/wiki/Drought 

https://en.wikipedia.org/wiki/List_of_droughts

Contraction / Desiccation cracks in the dry earth

• Droughts are events of sustained water shortages, including atmospheric, surface water, or ground water. 
• They can last for long periods (i.e. months or years), or are declared after 15 days. 

Drought severity world map

What are the different types of droughts? 

i. Meteorological Drought 

• This occurs when there is a prolonged period with less than average precipitation. 

ii. Agricultural Drought 

• This impacts crop production or the ecology of the range. It can manifest independently from changes in precipitation levels through either increased irrigation or soil conditions and erosion facilitated by poorly planned agricultural activities, which decreases the 

iii. Hydrological Drought 

• This occurs when water reserves in aquifers, lakes, and reservoirs decrease below a locally significant threshold. It can be caused by insufficient rainfall or diversion of water from one region to other regions. 

What are the causes of drought? 

a. Precipitation shortfall 

• If the mechanisms of precipitation production, such as convective, stratiform, and orographic rainfall, don't maintain precipitation levels adequately to reach the surface over a sufficient time, this leads to drought. 
• Other triggers of drought include significant levels of reflected sunlight, increased prevalence of high pressure systems, winds carrying continental air masses, and ridges of high pressure areas aloft that prevent thunderstorm activity. 
• Studies found feedback mechanisms such as local arid air and warm conditions can augment warm core ridging, as well as minimal evapotranspiration can aggravate drought conditions. 

b. Dry season 

• Due to the movement of the Intertropical Convergence Zone or Monsoon trough, wet and dry seasons emerge within the tropics. 
• Distinguished by its low humidity, the dry season increases the occurrence of drought. This dries up numerous watering holes and rivers, which forces the migration of grazing animals (e.g. elephants, wildebeests, zebras) in search of fertile lands. 
• Fraser (1994) stated that more water vapour is needed to lift relative humidity levels to 100% at warmer temperatures, since water vapour increases in energy at higher temperatures. 
• Studies pointed out that worsen drought conditions can worsen through periods of warmth that accelerate the speed of fruit and vegetable production, which increase evaporation and transpiration from plants. 

c. El Niño 

Impacts of warm ENSO episodes on different countries worldwide.

• During El Niño, parts of the Amazon River Basin, Columbia, and Central America experience drier and warmer weather events. 
• This exacerbates warmer and drier than average conditions during the winter season (December-February) in the Northwest, northern Midwest, and northern Mideast United States, hence decreased snowfall. 
• The same weather conditions also occur in African countries such as Zambia, Zimbabwe, Mozambique, and Botswana, as well as parts of Southeast Asia and Australia (e.g. Queensland, Victoria, New South Wales and Tasmania). 

d. Erosion & Human activity 

• Human factors such as farming, irrigation, deforestation, and erosion negatively influences the land's ability to capture and hold water. 
• Erosion is exacerbated by wind, which lifts tiny particles and carries them to another region (deflation), or damage other solid objects by abrasion. It usually occurs in regions with little or no vegetation, where there is inadequate rainfall to support vegetation. 
• An example of a sediment associated with wind erosion is loess. 

e. Climate change 

• Studies have expressed deep concerns about the significant association between climate change and prevalence of drought, which substantially impact agriculture worldwide, particularly in developing nations. 
• This exacerbates extreme events such as flooding and erosion, which would aggravate the impacts of climate change on society. 

What are the effects of drought? 

i. Environmental 

• Reduced surface and subterranean water levels 
• Reduced flow levels along with reductions below the minimum that exacerbates danger for amphibians. 
• Increased pollution of surface water 
• Dried out wetlands 
• Increased incidence and size of wildfires 
• Higher deflation intensity 
• Loss of biodiversity 
• Detriment to the health of tress 
• Appearance of pests and dendroid diseases 
• Decrease water quality since reduced water flows decrease dilution of pollutants and increase contamination of other water sources. 

ii. Economic 

• Reduced agricultural, forests, game and fishing output 
• Increased food-production costs 
• Decreased energy-production levels in hydro plants 
• Diminished water tourism and transport revenue 
• Issues with water supply for the energy sector and for the technological mechanisms in metallurgy, mining, as well as the chemical, paper, food, foodstuff industries etc. 
• Disruption of water supplies for municipal economics  

iii. Social 

• Adverse effects on people's health 
• Restrictions on water supplies 
• Increased pollution levels 
• High food costs 
• Stress caused by failed harvests, etc. 

iv. Other 

• Cyanotoxin accumulation within food chains and water reserves, leading to cancer. 
• Declined crop growth or yield productions and carrying capacity for livestock 
• Dust bowls, further eroding the landscape 
• Dust storms 
• Decreased electricity production because of decreased water flow through hydroelectric dams 
• Exposure and oxidation of acid sulphate soils due to decreasing surface and groundwater levels 
• Famine 
• Habitat damage impacting both terrestrial and aquatic wildfire 
• Hunger 
• Malnutrition, dehydration and related diseases 
• Mass migration, leading to internal displacement and international refugees 
• Snake migration, increasing the risk of snake bites 
• Social unrest 
• War over natural resources, such as food and water 
• Water shortages for industrial users 
• Wildfires 

When were the worst droughts ever? 

• 1540 Central Europe: Touted as "the worst drought of the millennium", with 11 months with no rain and temperatures of 5-7 ^oC above the average of the 20th century.
• 1900 India: 25,000 - 3.25 million people died due to the drought
• 1921-22 Soviet Union: Over 5 million people died of starvation
• 1928-30 Northwest China: 3+ million people died of famine
• Sichuan province, China with 5 million killed in 1936 and 2.5 million killed in 1941
• 1997-2009 Millennium Drought in Australia
• 2006 Sichuan province, China: ~8 million people and 7+ million cattle experienced water shortages
• 2015-2018 Cape Town water crisis in South Africa
• 2005 Amazon basin drought, the worst in a century.
• Recurring droughts in East Africa lead to desertification, hence ecological catastrophes, foot shortages in 1984-85, 2006, and 2011. Between 50,000 and 150,000 people died during the 2011 drought.
• 2012 Western Sahel drought inflicting fame on at least 10 million people due to heat waves impacting Burkina Faso, Mali, Mauritania and Niger.

D. Wildfires / Bushfires

https://en.wikipedia.org/wiki/Wildfire 
https://en.wikipedia.org/wiki/Bushfires_in_Australia
https://en.wikipedia.org/wiki/List_of_wildfires
https://en.wikipedia.org/wiki/Wildfires_in_the_United_States

https://en.wikipedia.org/wiki/Wildfire_modeling

• Wildfires / bushfires / wildland fires / rural fires are considered unplanned, unwanted, uncontrolled blazes in regions of combustible vegetation sparking in both rural areas and urban areas. 
• Depending on the vegetation ignited, a wildfire may be categorised as a brush fire, bush fire, desert fire, forest fire, grass fire, peat fire, prairie fire, vegetation fire, or veld fire. 

What are the causes of wildfires? 

-- Natural 

• Dry climate 
• Lightning 
• Volcanic eruption 

-- Human activity 

• Arson 
• Discarded cigarettes 
• Power-line arcs 
• Sparks from equipment 
• Contact with hot rifle-like fragments (under certain conditions) 
• Shifting cultivation: Significant land clearance and farming until the soil loses fertility, as well as slash and burn clearing. 
• Logging of forests exposes flammable grasses, as well as abandoned logging roads overgrown by vegetation posing as fire corridors. 
• Destruction of forests by herbicides, explosives, and mechanical land-clearing and burning operations by the military. 

-- Prevalence 

• In Canada and northwest China, lightning is the most common cause of wildfires. 
• In Africa, Central America, Fiji, Mexico, New Zealand, South America, and Southeast Asia, human activities heavily contribute to the ignition of wildfires, which includes agriculture, animal husbandry, and land-conversion burning. 
• In the rest of China and in the Mediterranean Basin, human carelessness is determined to be the most common of wildfires. 
• In the USA and Australia, both lightning strikes and human activities (such as machinery sparks, disposed cigarette butts, or arson) are the most prevalent causes of wildfires. 
• Coal seam fires can flare up unexpectedly and ignite adjacent flammable material. 

How do wildfires spread? 

The manner of which wildfires spread depend on a number of contributing factors such as the flammable material present, its vertical orientation and moisture level, and weather conditions. 

i. Ground fires 

• They are fuelled by subterranean roofs, duff, and other buried organic matter. Ground fires burn by smouldering, lasting for days or months. 
• e.g. Peat fires in Kalimantan and Eastern Sumatra, Indonesia were caused by a riceland creation project that unintentionally drained and dried the peat. 

ii. Crawling / Surface fires 

• They are fuelled by low-lying vegetation on the forest floor such as leaf and timber litter, debris, grass, and low-lying shrubbery. A 2014 study found these type of fires burn at relatively lower temperatures than crown fires (i.e. less than 400 ^oC (752 ^oF) and spread at a slower rate, unless it encounters a steep slope or blown from behind by strong winds. 

iii. Ladder fires 

• This incinerates material between low-level vegetation and tree canopies, such as small trees, downed logs, and vines. Examples include Kudzu and Old World climbing fern. 

iv. Crown, canopy, or aerial fires 

• These type of fires scorch suspended material at the canopy level, such as tall trees, vines, and mosses. 
• Graham et al. expounded that crown fires are sparked by a number of factors such as density of the suspended material, canopy height, canopy continuity, sufficient surface and ladder fires, vegetation moisture levels, and weather conditions during the wildfire. 

What are the physical properties of wildfires? 

a. Front 

This section maintains continuous flaming combustion, where unburned material contacts with active flames, or the unburned material is smouldered. The front flames warms both the surrounding air and woody substance via convection and thermal radiation. 

1. As water evaporates at its boiling temperature (100 ^oC, 212 ^oF), the wood becomes dry. 
2. The pyrolysis of wood occurs at 230 ^oC (450 ^oF) , which emits flammable gases. 
3. Wood then smoulders at 380 ^oC (720 ^oF) , or ignites at 590 ^oC (1,000 ^oF). 
4. Heat transfer from the wildfire front heats the air to 800 ^oC (1,470 ^oF), which preheats and dries flammable materials. This accelerates the ignition of flammable materials and aggravates the spread of wildfires. 
5. Higher temperatures and enduring surface wildfires may exacerbate flashover or torching, which involves tree canopies being dried and their subsequent ignition from below. 

b. Forward rate of speed (FROS) 

• The wildfire average FROS is approximately 10.8 km/hr (6.7 mph) in forests and 22 km/h (14 mph) in grasslands.
• Graham et al. observed wildfires can spread tangential to main front to develop a flanking front, or spread in the opposite direction of the main front by backing. 
• Shea (2008) stated that wildfires can jump or spot as winds and vertical convection columns carry hot embers and other burning debris through the air over roads, rivers, and other obstacles that act as fire breaks. 
• Torching and burning tree canopies may exacerbate spotting, and hot embers would ignite dry ground fuels around a wildfire, which would produce spot fires. 

c. Other 

• The increasing incidence of gigantic, uncontrolled wildfires in North America considerably influenced both urban and agricultural areas. 
• The physical damage and health crises manifested by wildfires devastate farm and ranch operators in impacted areas, which raised concerns from healthcare providers and advocates servicing the occupational population. 
• The stack effect dictates the flow of air currents within the immediate vicinities of wildfires. When the warm rises, wildfires generate intense updrafts that absorbs cool air from surrounding areas in thermal columns. 
• Studies found significant vertical differences in temperature and humidity augment the formation of pyrocumulus clouds, gale winds, and fire whirls that blow more than 80 km/h (50 mph). 

How does climate affect the risk of wildfires? 

• The risk of and behaviour wildfires can be influenced by a number of factors such as heat waves, droughts, climate variability such as El Niño, and regional weather events such as high-pressure ridges. 
• Westerling et al. (2006) found snowmelt and corresponding warming associated with increases in the length and severity of the wildfire season since the mid-1980s in Western USA. 
• Flannigan et al. (2005) thought the intensity and frequency of droughts increases with global warming, which increases the risk of intense and frequent wildfires. 
• Pierce et al. (2004) studied alluvial sediment deposits dating over 8,000 years and discovered warmer climate periods corresponded with severe droughts and stand-replacing fires. They concluded climate is an influential factor on wildfire incidence since a warmer climate makes the recreation of a pre-settlement forest structure virtually impossible. 
• de Souza, Costa & Sandberg found the burn rates smouldering logs are 5 times higher during the daytime since there is less humidity, hotter temperatures and faster wind speeds. 
• In 2019, the wildfires that affected Alaska (USA), Siberia, Canary Islands, Australia and the Amazon rainforest were significantly worse due to climate change and human activities such as deforestation and logging, and rarely arson. 

What do wildfires emit? 

• Wildfires emit abundant amounts of carbon dioxide, black and brown carbon particles, and ozone particle such as volatile organic compounds and nitrogen oxides into the atmosphere. These emissions are found to influence radiation, clouds and climate on local and global scales. 
• Studied also found wildfires emit semi-volatile organic compounds that separate from the gas phase to produce secondary organic aerosol (SOA) over a period of hours or days. 
• In addition to smoke, the harmful emissions can affect first responders and local residents, as well as air quality over long distances. 
• If wildfire smoke enters the planetary boundary layer (PBL), it may change the Earth's energy reserve rather than blending with the surface and affect air quality and human health. 
• A meta-analysis by Wiggins et al. (2020) revealed wildfire intensity and smoke emissions vary throughout the wildfire lifespan and emulates a diurnal cycle that peaks in the late afternoon and  early evening, which can be modelled using a monomodal or bimodal normal distribution. 

Describe the ecology of wildfires

-- Fire ecology 

This diagram illustrates prevalence of global fires during 2008 for August (top image) and February (bottom image), as detected by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite. 

• Bowman et al. (2009) conjectured that fire elicited evolutionary effects on a majority of ecosystems' flora and fauna. Pyne (2009) found wildfires occur more prominently in moist climates with extended dry periods that allow vegetation growth. 
• Examples include the vegetated areas of Australia and Southeast Asia, the veld in southern Africa, fynbos in the Western Cape of South Africa, forested regions of USA and Canada, and the Mediterranean Basin. 
• A 2017 report stated high-severity wildfires lead to the emergence of complex early seral forest habitats (or "snag forest habitat"), which are rich in species diversity instead of unburned old forest. 
• Furthermore, fire played a role in transferring nutrients from plant matter to the soil, and the fire's heat helps germinate particular types of seeds. In addition, the dead trees and early successional forests produced by high-severity fire were observed to support the highest echelons of native biodiversity situated in temperature conifer forests. 
• A number of studies concluded that the increased fire prevalence in fire-dependent areas can disrupt natural cycles, harm native plant communities, and promote the growth of non-native weeds such as Lygodium microphyllum and Bromus tectorum. 
• Since the invasive weeds are flammable, it increases the risk of future fires, which generates a positive feedback loop that raises the prevalence of fires and, to a greater extent, change native vegetation communities. 

-- Plant adaptation 

Left picture is 1 year after a wildfire and the right picture is 2 years after the same wildfire. They capture ecological succession after a wildfire in a boreal pine forest adjacent to Hara Bog, Lahemaa National Park, Estonia. 

• Plants in ecosystems prone to wildfires miraculously survive by adapting to their local fire regime. Examples of adaptations include physical protection against heat, boosted growth after a wildfire event, and flammable materials that promote fire and eliminate competition. 
• e.g. Eucalyptus plants contain flammable oils that fuel fires and hard sclerophyll to resist heat and drought as a way to ensure their dominance over less fire-tolerant species. 
• Pyne (2009) suggested dense bark, shedding of lower branches, and high water content in external structures are protective factors against increasing temperatures. 
• Keeley & Fotheringham (1997) found charred wood, smoke and heat are ingredient in the process of serotiny that involves germination and other plants such as orange butenolide. 
• Examples of plants emerging from the ground after periods of wildfires include Western Sabah grasslands, Malaysian pine forests, Indonesian Casuarina forests, Chamise deadwood, cape lilies, Sequioa, and Caribbean Pine. 

-- Atmospheric effects 

MODIS Aqua satellite image of smoke plumes and a pyrocumulus cloud northeast of Melbourne during the morning of 7th February 2009.

• A large proportion of Earth's weather and air pollution sits in the troposphere, which ranges from the Earth's surface to 10 km (6 mi) in height. 
• The vertical updraft of a thunderstorm or pyrocumulonimbus clouds can be strengthened around wildfires, which launches smoke, soot, and other particulates into the lower stratosphere. 
• Scala et al. (2006) presented satellite images that captured smoke plumes from wildfires, which illustrated plumes spreading over 1,600 km (1,000 mi). 
• Breyfogle & Ferguson (1996) stated computer-aided models such as CALPUFF can aid in predicting the size and direction of smoke plumes produced by wildfires by utilising atmospheric dispersion modelling.

This is a national map of groundwater and soil moisture in the USA. It illustrates the extremely low soil moisture associated with the 2011 fire season in Texas. 

• Studies found wildfires elicit adverse effects on local atmospheric pollution and increase atmospheric carbon dioxide levels. The particulate matter in the wildfire emissions associate with cardiovascular ad respiratory issues. 
• The National Centre for Atmospheric Research (2008) found increased wildfire by-products in the troposphere directly elevates ozone levels beyond safe levels. 
• For example, the 1997 Indonesia forest wildfires were estimated to have released 0.81-2.57 gigatonnes of carbon dioxide into the atmosphere. This accounted for 13-40% of the annual global carbon dioxide emissions from burning fossil fuels. 
• Reports indicated the toxicity of emissions increased over time because of the complex oxidative chemistry at work as wildfire smoke elevated into the atmosphere. 
• Baumgardner et al. (2003) presented an atmospheric model suggested sooty particles augmented the absorption of solar radiation during the winter months by around 15%. 
• Mufson (2019) estimated a wildfire burning in the Amazon would add approximately 38 parts per million to the Earth's atmosphere. 

Describe the history of wildfires 

• The first historical evidence of wildfires is rhyniophytoid plant fossils preserved as charcoal that date back to the Silurian Period (~ 420 million years ago), which was discovered along the Welsh Borders. This suggested smouldering surface fires began to appear before the Early Devonian period around 405 million years ago. 
• Glasspool et al. (2004) postulated, during the Middle and Late Devonian periods, there was low atmospheric oxygen and a reduction in charcoal abundance. 
• Supplementary charcoal evidence posits that wildfires lasted through the Carboniferous period. Later, the overall increase of atmospheric oxygen from 13% in the Late Devonian period to 31% by the Late Permian period increased the prevalence of wildfires. 
• Pausas & Keeley hypothesised that a reduction in wildfire-related charcoal deposits from the late Permian to the Triassic periods correlated with the reduction in oxygen levels. 
• Research on lepidodendron forests dating to the Carboniferous period discovered evidence of charred peaks, therefore crowned fires. In addition, gymnosperm forests dating to the Jurassic period shows evidence of frequent light surface fires. 
• Studies suggested the increase of wildfires during the late Tertiary period may be due to the increase of C₄-type grasses. Pausas & Keeley stated these type of grasses associated with mesic habitats, higher flammability, thus increased prevalence of fires. 
• A 2015 report listed a number of tree genera found in fire-prone areas such as Eucalyptus, Pinus and Sequoia, which are composed of thick bark to withstand fires and apply pyriscence. 

Human history with wildfires 

• The first use of wildfires by early humans were thought to occur around the Paleolithic and Mesolithic ages for the purposes of agriculture and hunting, which changed the pre-existing landscapes and fire regimes. 
• Meyer et al. (1995) hypothesised fire-associated debris flow in alluvial fans of northeastern Yellowstone National Park increased between the year 1050 AD and 1200, which coincided with the Medieval Warm Period. 
• Pitkänen et al. proposed a theory that the dendrochronological fire scars and charcoal layers in Finland associated with increases in the fire prevalence during 850 BC and 1660 AD that are attributable to human influence. 
• Charcoal samples discovered in the Americas implied a reduction in wildfire prevalence between 1 AD and 1750 compared to previous periods. 
• Between 1750-1850, human population growth and influences such as land clearing and practices increased the occurrence of wildfires in North America and Asia. 
• Marlon et al. (2008) described an association between the development of agriculture, increased livestock grazing and fire prevention efforts, and reductions of wildfires throughout the 20th century. 
• The number of natural and human-directed fires was found to have decreased by 24.3% between 1998 and 2015. A 2017 study suggested this finding may attribute to the transition from nomadism to settled lifestyle and intensification of agriculture, thereby reducing the use of fire for land clearing. 

Describe the modelling of wildfires 

https://en.wikipedia.org/wiki/Wildfire_modeling

A simple diagram of a wildfire propagation model

• In computational science, wildfires are modelled using numerical simulation with the aim to understand and predict fire behaviour. It can assist in wildland fire suppression, increase the safety of firefighters and the public, decrease risk, and minimise damage, as well as protect ecosystems, watersheds, and air quality. 

What are the environmental factors of wildfires? 

i. Weather 

• Wind increases the spread of fire in the same direction of the wind. 
• Higher temperature increases the burning rate of the fire. 
• Increased relative humidity (moisture) and precipitation can retard or extinguish fires altogether. 

ii. Fuel 

• Grass, wood and flammable material such as dry twigs. 

iii. Topography 

• Factors include orientation toward the sun, which affects the amount of energy received from the sun. 
• Slopes - Fires accelerate uphill rather than downhill, as well as in narrow canyons. Physical barriers such as creeks and roads can slow the spread of wildfires. 

What models of wildfires are there? 

• Models aim to balance fidelity, data availability, and quick execution in order to cater for a range of complex supercomputing challenges that need to be solved quicker than real time. 
• Since the 1940s, forest-fire models have been proposed by scientists but many chemical and thermodynamic questions associated with fire behaviour remain to be answered. 

i. Empirical models 

• Work by Fons (1946) and Emmons (1963) calibrated the quasi-steady equilibrium spread rate that calculates a surface fire's behaviour on flat ground in calm (no wind) conditions based on data of piles of sticks burned in a flame chamber or wind tunnel to describe other wind and slope conditions for the fuel combinations tested. 
• Canadian wildland fire growth models include FARSITE and Prometheus were develop to apply semi-empirical relationships and others that concerns ground-to-crown transitions in an attempt to evaluate fire spread as well as other parameters.

https://www.fs.fed.us/rm/pubs/rmrs_rp004.pdf

Source: FARSITE: Fire Area Simulator - Model Development and Evaluation, Mark A. Finney, 2004 

• The FARSITE model uses vectors to model fire growth and simulate wildland fires influenced by wind currents. 
• The research paper described a number of mathematical formulae such as Huygens' principle in an attempt to accurately calculate the fire's projected shape and direction of spread under a number of weather conditions such as humidity, temperature, wind direction, and topography. 

ii. Physically based models 

• These 2D fire spread models are based upon conservation laws that label radiation as the dominant heat transfer mechanism and convection, which indicates the effect of wind and slope, prompting reaction-diffusion systems of partial differential equations. 
• Complex physical models combine with computational fluid dynamics models with wildfire fire components and fire feedback loops upon the atmosphere. 

Examples of such models include:
- NCAR's Coupled Atmosphere-Wildland Fire-Environment (CAWFE)

- WRF-Fire (University of Colorado Denver)

- Coupled Atmosphere-Wildland Fire Large Eddy (University of Utah) 

- FIRETEC (Los Alamos National Laboratory) 

- WUI (Wildland-Urban Interface) Fire Dynamics Simulator (WFDS) 

- FIRESTAR 

• These models focus on different parameters and aim to improve out understanding of the fundamental aspects of fire behaviour, feedbacks between the fire and the atmospheric environment as the basis for the universal fire shape. 

What are the risks of wildfires? 

-- Human risk and exposure 

• Examples include human activities, weather patterns, availability of wildfire fuels, and availability of resources to suppress a fire. 
• A 2012 report postulated the rapid expansion of human developments into fire-prone wildlands increased the risk of wildfires occurring after a period of wildfire suppression. 
• Other factors such as global warming and climate change were alluded to as contributing to the temperature increases and prevalence of droughts worldwide, hence wildfire risk. 

-- Airborne hazards 

• Hazardous chemicals such as carbon monoxide, formaldehyde, acrolein, polyaromatic hydrocarbons and benzene can adversely affect human health. 
• Despite the high levels of carbon dioxide in wildfire smoke, its low toxicity makes it a low health risk. 

-- At-risk groups 

- Firefighters 

• Due to firefighters' occupational duties, they are exposed to hazardous chemicals at close proximity for longer periods of time. Studies found firefighters are exposed to concentrations of carbon monoxide and respiratory irritants that are above OSHA-permissible exposure limits (PEL) and ACGIH threshold threshold limit values (TLV). 
• Booze et al. (2004) found firefighters were exposed to a range of carbon monoxide (CO) and respiratory irritants levels, reaching 160 ppm of CO and TLV irritant index value of 10 (high). These values exceed OSHA PEL limit for CO at 30 ppm and the TLV respiratory irritant index limit of 1. 
• A 2013 CDC report stated over 200 wildland firefighters between 2001 and 2012 due to heat and chemical hazards. Other causes of death or injury mentioned are electrocution from power lines, equipment failures, slips, trips, falls, vehicle rollovers, heat-related illnesses, insect bites and stings, stress and rhabdomyolysis. 

- Residents 

• Communities adjacent to or surrounding wildfires are exposed to hazardous chemicals exacerbated by wildfires, which increases the residents' risk of indirect exposure through water or soil contamination. 
• The most vulnerable groups such as children (birth to 4 years), smokers, and pregnant women were most susceptible due to their compromised body systems even at low chemical concentrations and relatively brief exposure periods. 
• The Gazette Journal reported more than 350,000 Californians reside in places considered "very high fire hazard severity zones". 

- Foetal exposure 

• Studies conducted in Australia found male infants born in severe fire-affected areas had significantly higher average birth weights compared to control male infants. This implied that maternal factors directly influence foetal growth patterns. 
• When infants were exposed to air pollution during the gestational period, it disrupted the development of the epithelium of the lungs during the 2nd and 3rd trimester, which increases its permeability to toxins. 
• Furthermore, infants exposed to air pollution (e.g. PM2.5, NO2) during parental and pre-natal stages instigated epigenetic changes associated with the development of asthma. 
• In distressed communities, maternal exposure to chronic stressors associated with early childhood exposure to air pollution, neighbourhood poverty and childhood safety risk. This ultimately influences the allostatic load of the maternal immune system, which adversely affects their children in a number of ways such as increased vulnerability to air pollution and other hazards. 

What are the health effects of wildfires? 

• Wildfire smoke is composed of combustion components that includes carbon dioxide, carbon monoxide, water vapour, particulate matter, organic chemicals, nitrogen oxides and other compounds. 
• Particulate matter (PM) consists of minute dust and liquid droplets that are categorised into 3 types:

 i. Coarse = 2.5 - 10 μm 

• Coarse PM are filtered by the upper airways and accumulate there to trigger pulmonary inflammation. This exacerbates eye and sinus irritation, sore throat and coughing. 

ii. Fine = 0.1 - 2.5 μm

• Finer PM travel further into the respiratory system and clog the lungs and bloodstream. In asthma patients, PM_2.5 triggers inflammation and exacerbates oxidative stress in the epithelial cells, as well as apoptosis and autophagy in lung epithetical cells. This ultimately damages the lung and compromises its cell function, which are harmful for those with respiratory conditions such as asthma.

iii. Ultra-fine = < 0.1 μm

• Ultra-fine particles (UFP) enter the bloodstream and exacerbate the most severe inflammation and epithelial damage. This is significantly hazardous to the young, elderly and patients with chronic respiratory conditions such as asthma chronic obstructive pulmonary disease (COPD), cystic fibrosis, and cardiovascular conditions. 
• Exposure to UFP could manifest in bronchitis, asthma or COPD, and pneumonia. Common symptoms include wheezing, shortness of breath, and chest pain, rapid heart rate and fatigue. 

-- Epidemiology 

• Sutherland et al. (2005) found a significant association between the respiratory symptoms of COPD and the PM smoke emitted from the Colorado fire in June 2002. 
• Delfino et al. (2009) reported an increase in hospitalisations after the Southern Californian wildfires in October 2003 due to asthma symptoms exacerbated by inhalation of PM in smoke. 
• A 2017 epidemiological study by Liu et al. evaluated a 7.2% increase in the risk of respiratory hospitalisations during smoke wave days with high PM2.5 levels compared to non-smoke-wave days. 
• A 2006 Children's Health Study by Kunzli et al. discovered a direct correlation between wildfire smoke exposure and eye and respiratory symptoms, medication use and GP visits. 
• Holstius et al. (2012) discovered pregnant mothers during wildfire events gave birth to babies with slightly lower average birth weight compared to those who weren't exposed to wildfire smoke during birth. This indicated that pregnant women were adversely affected by wildfires compared to sterile women. 
• Johnstone et al. (2012) estimated roughly 339,000 people die from the effects of wildfire smoke worldwide every year. 
• Liu et al. (2017) constituted evidence for the role of PM2.5 chemical composition on the estimates of human health outcomes compared to other sources of smoke. 

When and where were the deadliest wildfires? 

-- Australia 

-- USA 

-- Canada 

-- Rest of the World 

• Whenever it is summer or sweltering in your area, it is important to wear a pair of sunglasses (sunnies), slip slop, slap some sunscreen on your skin, consume copious amounts of cool water with the optional icy treat such as ice cream or icy pole. 
• If there is a wildfire emergency near your area of residence, remain calm, follow all evacuation procedures and leave your home as early as possible to ensure your own and your family's health and safety. 
• Final note: If you're expecting a baby and planning a gender reveal party, I would advise against using fire crackers or fireworks at a venue surrounded by forest on a dry hot day. 

The next part of the natural disasters blog series will be about the coldest natural disasters.