UNPRECEDENTED PRE-MONSOON STORMS IN INDIA
How can we say that the pre-monsoon season in 2018 has witnessed unprecedented storm activity?
- Since February this year India has experienced 44 storms all over the country (16 States)
- The wind speed, many times, exceeded 130 km per hour (when the threshold speed for storms is 90-100 km per hour).
- Even though storms are common for North and north western region of India occurring in the months of April to June, but they are generally accompanied with little or no rain. But this time it was heavy rain, hails and strong winds which increased the intensity and impact of the storm
- The severe impact of this storm on the lives, livelihood, livestock of the people has made it unprecedented
What was the impact of this surge in storms?
- The storms caused massive damage to the property – around 5000 houses collapsed
- Massive loss of life – More than 400 deaths and over 700 injured
- The dust storm affected people’s livelihood besides killing their livestock and destroying their crops
- There is lack of basic infrastructure – water and electricity – as the electric poles are uprooted due to storms and people cannot use the water pumps in the absence of electricity
Reasons behind the phenomena
Unusually hot conditions
- Temperatures of over 40 degree Celsius have been observed in northwest, central and east and north peninsular India. Maximum temperature was upto 8 degrees celsius above normal. This led to an intense heat wave.
- Interaction of hot air near the surface with colder winds from the western disturbances gave rise to intense and widespread storms
- For example, in Rajasthan, one of the worst affected states 46 degree Celsius temperatures were recorded and a record-breaking 50 degree Celsius was recorded in neighboring Pakistan
Western Disturbances (WD)
- These are extra tropical or temperate cyclones originating in the Mediterranean region that brings sudden winter rain to the northwestern parts of the Indian subcontinent
- While the western disturbances normally peak between December and February, a greater number of active WD have been observed in spring and summer months
- Instead of the normal 2-3 active WD seen during the month of April and May, over the past month and a half at least 10 separate active WDs have been observed.
- WDs carry high-velocity winds that agitate the atmosphere and aggravate storm conditions
- Swirling motion of the winds caused due to low-pressure area is called cyclonic circulations
- In the build-up of the massive storms at the beginning of May, five separate cyclonic circulations were observed across the country
- A trough is an extended area of low pressure.
- This is where moisture laden winds from the Bay of Bengal met hot and dry air from central and western India. These winds also came in contact with the cold front that develops due to active WDs.
- The confluence of these different winds culminated in intense and widespread storms across the Indo-Gangetic plain.
- Similarly, a North-South trough was formed from Bihar to Northern Tamil Nadu along which stormy weather was observed in Telangana, Andhra Pradesh and some parts of Karnataka
- Easterly winds from the Bay of Bengal carry moisture and is associated with pre-monsoon thunderstorms in the eastern coast. But this usually happens in the winter months. This year, the easterlies have continued well into May and have interacted with the WDs owing to the east-west trough. This fuelled intense activity over large parts in south india.
Anomalies at sea surface
- The anomalies in sea surface temperatures (i.e 1-2 degree warmer waters) over the Bay of Bengal and the Arabian sea have spurred greater moisture transfer than usual by the easterly and westerly winds (respectively) causing the spate of storms.
Why are these storms climatologically atypical?
- While the timing of the storms was as expected, their extent and intensity surprised many a scientist (explained above)
- Unusually hot weather conditions ushering in heat waves across north, northwest and central India (explained above)
- An unexpected activity of Western disturbances (explained above)
- The surprising behavior of Easterly winds (explained above)
- The anomalies in the sea surface temperatures over Bay of Bengal (explained above)
Why were the forecasts by IMD inaccurate?
Outdated forecasting models
- India uses the (obsolete) NowCast model.
- Switch to the contemporary ‘Unified Model’ is hamstrung by lack of data.
Inadequate Doppler radars
- IMD has installed only 25 doppler radars so far across the country
- These cover only 12.5% of India’s land area.
Poor maintenance and upkeep of instruments.
- Some of the Doppler radars were not functioning when the storms hit.
The differences in the nature of the storms over the Indian region made the predictions difficult
- Unlike the climatic-scale storms seen in the Middle-East, the recent storms in India had weaker vertical torque but strong horizontal torque.
Way ahead for India
- Many initiatives have been taken by countries who face similar challenges to control the effects of a dust storm. India needs to learn from their experiments.
- Example- The great green wall that has been developed by China along the Mongolian drylands, this massive corridor of vegetation purportedly acts as a windbreak for intense sandstorms emanating from the north and reduces the transport of dust further south thereby limiting the possibility of desertification
- Besides learning from the interventions of other countries the most important step for India is to develop its weather forecasting and monitoring infrastructure