The Indo-Gangetic Plains stretching from north India all the way to the east have been witnessing very poor air-quality during the pre-monsoon season (March to May) for the past few years. Delhi, due to its geographical location, is placed in the middle of the dust-laden Westerly winds originating from the Arabian Peninsula or the Thar Desert. The Westerly winds typically bring loose sand and soil particles, picked up from the Arabian Peninsula or the Thar Desert in northwestern India, to the Indo-Gangetic Plains. Recent scientific studies reveal a change in the long-term wind patterns over Delhi in the past few years.

Dr Gufran Beig of the System of Air Quality and Weather Forecasting and Research (SAFAR) at the Indian Institute of Tropical Meteorology (IITM), Pune told Down to Earth that this change in the wind pattern is having major implications on the pollution levels in the city, revealing a striking increase in the frequency of winds coming in from the north-west direction in the past few years. It was further stated that there could be many reasons for this change in wind patterns, with one reason attributed to major changes in the retreating monsoon from the region and the anticyclonic circulations that are formed during this period.

The Aravalli mountain range prevented the advance of dust from the Thar desert towards the fertile soils of eastern Rajasthan and the Indo-Gangetic plains, thereby stopping dust from entering Delhi. However, deforestation in the Aravalli mountain range has recently led to large tracts of the mountain range turning into desert-like land and the consequent inflow of more dust particles into Delhi by strong winds. If this land degradation continues, it is likely that the dust storms will get more intense and dangerous in the coming years, as there will be fewer trees or vegetation to act as a barrier for the rapidly-advancing winds.

The urban heat island effect leads to the formation of low pressure over Delhi, causing the movement of winds towards the capital. The direction of the wind in such a scenario is west-south-west bringing in dust from Rajasthan. The wind drifting towards the National Capital Region (NCR), causes a dip in the air quality in Delhi, leading to an average concentration of coarser particles like PM10 (particulate matter) which is three times more than the prescribed standard. The result of this depreciating air quality has far-reaching effects on human health and leads to loss of lives, livestock and damage to infrastructure. In May 2018, dust storms claimed the lives of some 100 people and injured around 200 people. However, this unacceptably high mortality due to the deadly combination of heat waves and dust storms during the pre-monsoon months has become a common occurrence.

Addressing this ascending issue,  Dr Sudipta Sarkar, a scientist at the NASA Goddard Space Flight Centre and a member of the research team, while speaking to India Science Wire explained the effects of the phenomenon. According to him, “The dust storms have both short and long-term impacts and some of the short-term impacts can have very real consequences for human health. Mainly, the damage to air quality is seen to come from an increase in aerosol concentration, increases in respirable suspended particulate matter like PM 10, PM 2.5 and also temporary fluctuations in tropospheric greenhouse gases like carbon monoxide and ozone.” He further added, “Ozone is especially important as the interplay between surface ozone and dust events have not been fully documented before and in that respect, we show that there is definitely some inter-relationship and you would expect some level of surface ozone increase and consequent health impacts.”

Table showing the prescribed National Ambient Air Quality Index (AQI )

According to SAFAR and the Central Pollution Control Board (CPCB), the Air Quality Index or AQI (see above table) in the national capital is mostly recorded at above 300 which falls in the ‘very poor’ category, and it deteriorates further during the pre-monsoon season due to the dust storms. On analysing the various aspects of climatic changes taking place globally, it can be observed that the pre-monsoon dust storms extending over large parts of India are not out of the ordinary, but are the result of the confluence of multiple factors. Taking into consideration the reasons and effects of the changing climatic conditions, it will be safe to say that this change in the course of the weather is an additional indication of global warming and its impacts on the Indian monsoon.

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