A thunderstorm is a storm characterised by the presence of lightning and thunder. When the temperature rises, hot and moist air rises upwards- in what are known as updrafts. At the same time, the cool air sinks downwards, and these are called downdrafts.

Collision between the updrafts and downdrafts creates cumulonimbus clouds and it produces lightning and thunder. Thunderstorms occur almost everywhere on the earth's surface, one of the most dangerous convective weather events. An estimation of more than 1600-2400 thunderstorms occur at any moment and 50,000 each day, around the globe.

Geographic location of Bangladesh is an indicated zone of natural disasters like tropical cyclones, drought and flood. Bangladesh is also a frontline state facing potentially great disruption to human settlements wrought by long term climate change. It is particularly vulnerable to the rising sea level caused by global warming, with about a quarter of its population living in coastal areas at risk of catastrophic flooding by 2050, according to new research published in the respected scientific journal Nature last month.

It strikes, and strikes again

All thunderstorms produce lightning. Lightning injury is a global public health problem representing the leading cause of weather-related death after tornadoes, flash floods and hurricanes. The injuries cause high mortality and significant long term morbidity.

A thunderstorm, also known as an electrical storm, lightning storm, or thunder shower, is a storm characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder.

Thunderstorms occur in a type of cloud known as a cumulonimbus. They are usually accompanied by strong winds, heavy rain, and sometimes snow, sleet, hail, or, in contrast, no precipitation at all.

Thunderstorms may line up in a series or become a rain band, known as a squall line. Strong or severe thunderstorms include some of the most dangerous weather phenomena, including large hail, strong winds, and tornadoes. Some of the most persistent severe thunderstorms, known as supercells, rotate as do cyclones.

There are three basic types of thunderstorm. They are- (a) single cell, (b) multi-cell and (c) super-cell thunderstorm.

Single Cell Thunderstorm: Short lived (30-60 minutes) with one updraft that rises rapidly through the troposphere.

Precipitation begins at the mature stage as a single downdraft. When the downdraft reaches the surface, it cuts off the updraft and the storm dissipates. They are having weak vertical and horizontal wind shear.

In Bangladesh, moist and hot air flowing from the Bay of Bengal and colder, heavier air descending from the Himalayas have long collided in lightning-sparking thunderstorms.

Dewan et al. [2017] identified 3,086 fatalities from 1990 to mid-2016, for an annual average of 114 fatalities caused by lightning in Bangladesh over the entire period. The quite severe spike in recent years is apparent from the fact that if we look at the data from 2010 , the average number of fatalities per year from lightning strikes more than doubles to 260.

The problem prompted the government in 2016 to add lightning strikes to the country's list of official types of disasters, which includes floods, cyclones and storm surges, earthquakes, drought and riverbank erosion, among others.

Last year, around 360 people in Bangladesh were killed by lightning strikes - more than by floods or cyclones, according to the Disaster Management and Relief Ministry.

Our sister newsagency UNB recently reported that at least 126 people were killed by lightning strikes across the country in May and June this year, which emerge as the most dangerous months of the year for this new addition to the country's official list of natural disasters. Together, these two months smack in the middle of the year accounted for more than half the total number of casualties caused by lightning in the first 8 months of the year (246).

'Saving Society and Thunderstorm Awareness Forum', an NGO, presented the numbers, that it said were compiled from at least 10 local and national newspapers, some online portals and television channels, at a press briefing in September.

Most of the victims were killed while fishing or bringing cattle back home from the field. Some of the victims died while sleeping in houses made of corrugated tin-sheets, and standing under trees that got struck.

Dr Md Abdul Mannan, Meteorologist of Bangladesh Meteorological Department (BMD), told Dhaka Courier that the extent of lightning has increased much across the country in the last couple of years due to changing pattern of lightning formation area, lightning occurrence period and occurrence time of lightning.

Forecasting a split-second

Till the last few years, he said, Bangladesh Meteorological Department (BMD) is carrying out numerical weather prediction models and trying to determine the position of thunder cloud and lightning.

Besides, he said, the BMD is carrying out the work of identifying the lightning-prone areas of the country through overall observation. The department through analyzing the information received from observation and mathematical model, is also working on determining the severity of lightning.

"Based on these information and data, the weather department is giving lightning forecast 24 hours before and also disseminating necessary warnings in the media for public awareness," said Dr Mannan.

"The forecast of the recent time and warning signal is becoming more accurate than the past which, if followed by the people, can mitigate or minimise the loss of life and property to some extent," he pointed out.

He informed that the country's north-eastern region particularly Mymensingh and Sylhet divisions are the lightning-prone areas. However, in the recent time, its severity has been expanded up to the central region particularly towards Dhaka division and Cumilla and Noakhali regions.

The long and short of it

Previously the formation area of lightning was in the Bihar and West Bengal of India. However recently, the lightning formation area is being seen in the West Bengal and adjoining western part of Bangladesh.

As a result, the energy within the lightning has the potential to strike all over Bangladesh and as a result its striking areas are seen in Bangladesh's central region and its surrounding areas. This means the severity of lightning and extent of damage are seen to increase.

With long-term planning, loss of lives and damage due to lightning will come down. This draws on the observation that the increased fatalities have coincided with a period of unabated deforestation all over Bangladesh. Tall trees especially in rural areas can act as a protective shield. Lightning usually strikes the tallest object in a vicinity. It makes sense that the tallest object is most attractive, because it is the easiest path for the lightning to take. Trees attract lightning because they provide a path for lightning to travel from the storm cloud to the earth.

The tall trees reduce the damage of lightning. The palm tree (Taal) would help reduce the losses of lightning as it does not fall down easily even during strong winds. Palm tree plantation may therefore be increased. Government has already taken initiative to plant palm trees all over Bangladesh - the Disaster Management Ministry is supporting the sowing of 4.8 million palm trees nationwide, up from 1 million in a previous plan.

The short-term plan includes development of forecasting system and at the same time, accurate forecast needed to be disseminated. The increase of short-term plan also included public awareness raising.

"Department of Disaster Management can raise awareness about the lightning and its impact through distributing posters in different areas, holding of meetings, seminars and workshops," said Dr Mannan, adding that these steps would help all concerned to play the desired role.