A widely accepted definition characterizes natural hazards as “those elements of the physical environment, harmful to man and caused by forces extraneous to him” More specifically the term “natural hazard” refers to all atmospheric, hydrologic, geologic (especially seismic and volcanic), and wildfire phenomena that, because of their location, severity, and frequency, have the potential to affect humans, their structures, or their activities adversely.
There is evidence to suggest that the frequency of such natural hazards is increasing. Reported disasters between 1960’s and 1980’s which Blaikie et al collated in1994 showed a definite trend of an increase in the frequency of natural hazards. For example, in 1960’s there was one avalanche classified as a natural disaster but in 1970’s this number increased to 4 and this number increased four fold again to make 16 avalanches classed as ‘natural hazards’ in the 1980’s. Another obvious trend is that the number of volcanoes in a twenty year period is appearing to almost double – 13 in 1960’s, 25 in the 1970’s and 55 in the 1980’s. In fact, the total of natural hazards in 1960’s (including epidemic, drought/famine, avalanche, wind storm, flood, volcano, landslide and earthquake) was only 23.7% of the natural disasters occurring in the 1980’s.
Below I will examine three well-known natural disasters that are increasing in frequency and suggest how human activities may exasperate them thus increasing their numbers.
Floods as natural hazards are also more than doubling every 10 years – the 1960’s saw 142 floods that caused damage to humans and their activity, 356 in 1970’s and an enormous 603 floods in 1980’s were classed as natural hazards. Floods could be increasing in frequency for a great number of legitimate reasons.
1st) The capacity of the river may be decreasing due to human activities. A dam may have been created in order to control floods or to generate hydroelectric power. An example of this is the Aswan High Dam just north of the border between Egypt and Sudan, which was completed in 1970. The creation of a reservoir (Lake Nasser) has lead to problems where sediment is collecting at the bottom and its capacity is reducing every year. This will obviously lead to floods in the future, as there will be no channel for the water to be stored.
2nd) The enhanced greenhouse effect has been blamed for an increase in floods. This is caused by increased human use of CFC gases and methane. Also increased use of fossil fuels such as oil (petrol) has increased the amount of carbon dioxide in the atmosphere. Simply, this forms a ‘blanket’ of gases trapping heat from the sun from escaping the atmosphere and thus making the earth warm up like a green house. By the 2050 the temperature is estimated to have risen by 3 degrees Celsius. This is expected to produce 150 million environmental refugees by 2050 due to droughts and flooding. In the last 100 years the earth’s temperature has increased about half a degree Celsius. According to the U.S. Environmental Protection Agency (EPA) the sea level has risen six to eight inches (15 to 20 cm) in the last 100 years. This is believed to be due to the melting of ice caps. This increased amount of liquid water in the water cycle would logically increase flooding the flooding risk.
3rd) The increase in urbanisation will also effect flooding. Firstly roads and large expanses of cemented areas such as pedestrianised CBD do not allow water to infiltrate into the soil. When the water is channelled into the soil or drainage areas then the soil becomes saturated very quickly. There is therefore less of a lag time. As the water can not infiltrate into the available soil quickly enough or there is not very much available soil then it is likely that water will travel as surface runoff into a channel flow. Will therefore result in flooding. This is heightened by deforestation which prevents interception by leaves and reduces the amount of stem store (water stored inside the tree). An example of this the flash flood disaster that killed over 83 people on a campsite in Spain on 8th of August 1996 which was impossible to forecast. Local people were blamed for the localised flooding as recent deforestation had occurred at the Pyrenean foothills. Water and mud had been impounded behind a small bridge which, when burst, resulted in a huge torrent rushing down the valley. In addition, the design of buildings is to get rid of water as soon as possible – the curvature in a road and the slanted roofs of houses. This exasperates the impact of urbanisation on flooding.
Drought and Famine
This is primarily caused by persistent sub-tropical high-pressure systems (the Sahel in Africa) and El Nino/ ocean surface temperature changes (cause of droughts in California and Chile) however drought problems can be agitated by human activities.
1st) Groundwater abstraction would mean that there would be an increase in soil temperature as water has a cooling effect and therefore the soils would be at risk of baking and becoming so hard that it is impossible to cultivate. Over extraction of water from Lake Chad in Africa by four countries – Sudan, Chad, Niger, Nigeria has reduced it to one 5th of its original size. This has reduced soil fertility in the area around the lake and will result in its disappearance very soon. In addition unwise irrigation leads to salinisation; where the soil is so salty that it cannot be used to grow things on or be used for animal rearing.
2nd) Over grazing can mean that animals trample soil thus compacting it and remove nutrients from the ground. Unwise cultivation would result in damaged surface soil and subsoil which would mean that there was a loss of nutrients. There would also be a reduction in the water holding capacity of the soil thus encouraging drought.
The number of landslides has increased from the 1960’s to 1980’s. In the 1960s – 23, 1970’s – 50 and in the 1980’s – 81.Landslides usually involve the movement of rock or debris along a slip surface. Human activity can influence landslide activity
1st) In urbanised areas there is an increased chance of landslide activity. The weight of people’s homes and possessions force the land downwards thus encouraging landslides. Shantytowns are particularly vulnerable as they are developed on deforested slopes. The lack of trees means that the soil looses its structure and is not held in place by roots and its therefore susceptible to rotational sliding. Deforestation in the Mediterranean has resulted in catastrophic land sliding especially in Italy.
2nd) Landslides that are more fluid (mudflow) can be caused by an increase in rainwater or encouraged by storm surges. The causes of this hazard is explored above.
3rd) In addition, landslides can be called Lahars, which are caused by Volcanic activity. This is because sediment takes on the characteristics of water, which is called liquefaction. This often has dramatic consequences. An example of liquefaction is Loma Prieta Earthquake in 1989.
Such hazards that are exasperated by human influences are termed ‘quasi-natural hazards’ as they are not as entirely ‘natural’ such as earthquakes and volcanoes resulting in tectonic activity. However it is difficult to separate natural and the aforementioned quasi-natural hazards.
It must also be noted that a ‘natural hazard’ only becomes a hazard when it directly impacts upon humans and their activities, otherwise it is just a natural phenomenon. Therefore, the increase in human population and the increase of people in areas susceptible to natural hazards will impact upon whether it is deemed a natural hazard or a natural phenomenon. For example, I suspect that the increase in avalanches as a natural hazard is due to the increase in the skiing and mountain walking tourist industry. Avalanches that would occur naturally due to mass movement such as rotational slip will affect humans who are enjoying mountain activities and therefore will be classified as a natural hazard under recognised definitions.
In addition, people using the area put pressure on loose soils and therefore maybe responsible for the avalanche itself. However, these people may demand aid and the avalanche may affect tourism business and property so again, it is deemed a natural hazard. Another example is drought. Due to desertification thousands of people in the Sahel are forced to give up nomadic traditions and live near a definite water supply (such as Lake Chad). As thousands of people use this water source for human consumption, crop irrigation and farm use it is unsurprising that the Lake is drying up. Over population in an area that can not sustain such numbers will result in sever droughts and famine as the soil becomes unusable and dry as water stores diminish.
In the year 2001, natural hazards killed over 25,000 people and caused $36 billion in damage worldwide. Unfortunately, the cost of natural hazards is increasing dramatically. In the 1990’s, the average cost of all natural hazards in the United States doubled from $25 billion to $50 billion per year. In some countries (including the U.S.), even if your community does not suffer from any natural hazards in a particular year, federal disaster assistance to other communities is partially paid for by everyone’s taxes. Therefore the increase of natural hazards will impact upon many people, directly and indirectly, so the frequency of such events need to be recorded to see if there are any immediate correlations that can prevent such dramatic phenomenon. In addition, the recording of such hazards may allow correlations to be found that can be used as a management tool to prevent human activities agitating natural hazards.