High pollution levels can alter rainfall patterns, Delhi-NCR at risk: Analysis

A recent analysis by Climate Trends, a Delhi based communications initiative building a narrative around climate ambition and low carbon development pathways, highlighted how high pollution levels impacted monsoon patterns in a region.

High pollution levels not only pose a health risk to people but over time, it can also reduce the southwest monsoon rainfall by around 10-15% in the country, a new analysis has found.

Signs of erratic monsoon patterns are already visible in Delhi and the neighbouring areas. (HT File)

A recent analysis by Climate Trends, a Delhi based communications initiative building a narrative around climate ambition and low carbon development pathways, highlighted how high pollution levels impacted monsoon patterns in a region. The analysis said with the levels of toxic pollution increasing, in the coming years, monsoon rain may reduce by at least 10%.

“Air pollution is likely to decrease the southwest monsoon rainfall by 10%-15% for the entire country. Meanwhile, some places might even see rain drop up to 50%. It will also impact the dynamics of monsoon like cause a delay in onset,” said Dilip Ganguly, associate professor, Centre for Atmospheric Sciences, IIT-Delhi, who is one of the contributors to the analysis.

Explaining the reason, he said, “Air pollution does not allow the landmass to warm up to the required levels. Due to the presence of pollutants, heating of land takes place at a slower rate. For instance, the required surface temperature is 40°C, while the presence of air pollution will result in restricting temperature up to 38°C or 39°C.”

Signs of erratic monsoon patterns are already visible in Delhi and the neighbouring areas.

Scientists at the India Meteorological Department (IMD) and private weather forecasters said that over the last decade, instead of receiving uniform rains, Delhi has been receiving short and intense rainfall. The number of rainy days has also reduced from around 15-17 between the years 2000 and 2009, to around 10-12 over the last 10 years.

This year, Delhi saw only five rainy days in August. But in these five days, the city received 214.5 mm rainfall, a 3% surplus, the bulk of which was concentrated on August 21.

The report also reiterated what Delhi is witnessing. The findings said that “although air pollution is impacting mean monsoon rainfall for India, it is the Indo-Gangetic plains which seem to be in a tight spot.”

“...From March-May, the land surface gets heated due to which the strength of the inversion layer reduces, bringing down the pollution levels. However, during that time, dust from western Rajasthan and the adjoining desert region of Pakistan reaches the Indo-Gangetic plains. This along with local emissions leads to an increase in summer time pollution,” said Krishnan Raghavan, scientist, Indian Institute of Tropical Meteorology, and lead author on IPCC working group-one report.

He said, “The geography of the north-western plains including Delhi-NCR is also not supportive. The entire Himalayan region guards the Indo-Gangetic plains, which does not allow pollutants to escape and acts as a barrier.”