Natural Hazard in Bangladesh

NATURAL HAZARD

Natural Hazard any natural event which has an adverse socio-economic impact on the human being. Alternatively, an extreme natural event, such as a cyclone and earthquake or flood,that is not caused by human beings. These are naturally occurring phenomena that only become hazardous due to the intervention of human infrastructure. The vulnerability of human infrastructure to destruction (risk) by a disaster is also an important factor in understanding natural hazards. The distribution and impact of natural hazards is unequal with greatest loss of life and property in the developing part of the world. This is not because of greater hazard frequency but simply because of greater vulnerability (Banglapedia, 1999).

Natural hazards can be identified into three broad groups such as atmospheric hazards caused by atmospheric processes (storm, cyclone, Nor’weste, tornado, hurricane, Drought etc), exogenic hazards caused by the earth surface processes (flood,river bank erosion, coastal erosion, land slide, soil erosion,  and groundwater contamination), and endogenic hazards caused by internal earth processes (earthquake and volcanic eruption). On many occasions there are overlaps between these different events. Natural hazards can be profiled against seven basic criteria viz. event magnitude, frequency of occurring, duration, areal extent, speed of onset, spatial dispersion and temporal spacing.

In Bangladesh the risks of atmospheric and exogenic hazards are high whereas risk from endogenic hazards are relatively low. Cyclone, flood, riverbank erosion, coastal erosion, landslide, drought and groundwater contamination are major natural hazards. Among the endogenic hazards, Bangladesh have risks from earthquake only, not from volcanic activity. The greatest natural hazard currently being confronted by Bangladesh is the contamination of groundwater by Arsenic. Table 1 shows the major natural hazards, its causes and impact in Bangladesh.

Table 1: Major Natural Hazard in Bangladesh

Major type	Sub-types	Causes	Probable Impacts
Flood	Flash flood Normal flood (river and rain fed)	Heavy rain in & outside Bangladesh (GBM basin area) Silted riverbeds Flood embankment failure Haphazard construction of roads/rails, culverts etc. obstructing natural flow of flood water Topographical cause (for flash flood)	Reduce crop production Threats food security Increase un/under employment Damage settlements and physical infrastructure Increase in frequency and intensity of riverbank erosion Threats fish, poultry, livestock and other small industries Increase health risks Drainage congestion and water logging
Storm	Cyclone associated with tidal surge Tornado Nor’wester (Kalbaisakhi) Hailstorm	Relative location of landmass & sea Funnel shaped coast Deltaic lowlands Broken coast with many rivers & canals Dense settlements	Heavy casualties (death and injured) Heavy loss of livestock Destroy/damage settlements, industries & physical infrastructure Destroy standing crop and affect agriculture  Salinity intrusion Severely affect health & livelihood Damage forest and homestead trees Increase un/under employment Damage ports, fishing & tourism industry Damage fresh water reservoirs (ponds, beels, khals)
Drought	Seasonal Occasional (non-seasonal)	Topography (uplands) Soil permeability Deforestation Inadequate or low rainfall Excessive withdrawal of ground water Cross border diversion of river flow &construction of barrage, dam & embankment Over population	Loss of production (crop, livestock, dairy, fish, timber) Increase un/under employment Threats food security Reduce wetlands & biodiversity Increase incidence & severity of fire Ground water level drops affecting agriculture, fisheries, forests, health etc. Salinity intrusion Disrupt irrigation, water transport & power production Food crisis, malnutrition and famine
Erosion	Riverbank erosion Coastal erosion Afal (Haor region settlement erosion in flood season)	Deltaic location with soft soil Embankment & levee failure Meandering and braided rivers Too many confluences   Silted riverbeds and narrowing channels Cross border riverbank protection activities Inadequate, improper & lack of timely protection measures Weak ground coverage & dense settlements	Loss of land, property and livelihood Increase poverty, landlessness & vulnerability Increase un/under employment Increase out-migration & homeless floating people Disintegration of social organization (kin network) Increase insecurity of children, women & elderly people Damage infrastructure
Earthquake	Earthquake	Close to the Himalayan range High density of people & buildings Poor quality of infrastructure (low resilient)	Heavy causalities (death & injury), particularly in big cities like Dhaka, Chittagong and Sylhet Severe damage and destroy of houses, physical infrastructure, including roads, bridges & railways Threats of explosions (gas/gasoline, oil) & fires Severe health risk and disruption of health & other utility services Decrease GDP and economic growth Increase poverty and social unrest Increase un/under employment In case of tsunami, severe destruction of properties, environment & human causalities in the coastal belt
Rain	Heavy rain (sudden or prolonged period) Irregular rain	Humid monsoon climate	Drainage congestion and water logging
Sea level rise	Sea level rise (multi-hazards)	Global warming of atmosphere Deltaic location & very low elevation Funnel shape coast High density of settlement	Land loss due to permanent inundation Wider intrusion of saline water Reduce fresh water wetlands, biodiversity & mangrove forest Production loss (crop, fish, livestock, timber) Disrupt ports and tourism industry Stagnant flood water and water logging Increase impact of tidal surge Loss of livelihood and severe health risk Increase involuntary migration and refugee flow Needs massive repairing work and heightening settlements, roads, rails & embankments
Heat & Cold waves	Heat waves Cold waves	Hot and cold monsoon climate	Croup failures, death
Arsenic	Arsenic contamination		Adversely affects the health

Therefore, the people in the developing countries are at high risk than those of developed countries. Combining the risk factor the natural hazard can be defined as the probability of a change in the natural environment of a given magnitude occurring within specified time period in a given area while the associated risk is the consequent damage or loss of life, property and services. The frequency of major hazard appears to have increased since 1960 and the number of people killed each year has decreased at a rate of about 6% and the loss or property has also decreased steadily. This has taken place owing to increased awareness and better hazard management. The increase in the frequency of hazard can be assigned to such factors as better global news coverage, increasing population, increasing urbanization and increasing natural degradation. Natural hazards are now being considered as of global importance and global efforts are being made to mitigate them.