Context: Scientists have found that aerosols like black carbon and dust, which makes the Indo-Gangetic Plain one of the most polluted regions of the world, have contributed to increase in the incidents of high rainfall events in the foothills of the Himalayan Region.
Key Points

• A team of researchers from National Institute of Technology Rourkela, Leipzig Institute for Meteorology (LIM), University of Leipzig, Germany, Indian Institute of Technology Madras, Indian Institute of Technology Kanpur supported by the Department of Science & Technology, Government of India under DST Climate Change program have highlighted the crucial role of the aerosol direct radiative effect on high precipitation events over the Himalayan region.

Indo-Gangetic Plains

• The Indo-Gangetic Plain is also known as Indus-Ganga and the North Indian River Plain. It lies between the great northern mountain and peninsular plateau and is formed by three major rivers – the Ganges, the Indus, the Brahmaputra and their tributaries. It covers a large area of about 7, 00,000 sq. km in Northern and Eastern India.
• The region is known for high aerosol loading, a large part of it is black carbon and dust largely owing to stubble burning and vehicular emissions.
• This presents an opportunity for analysing how aerosol impacts extreme rainfall events, particularly when an air mass is forced from a low elevation to a higher elevation as it moves over rising terrain technically called orographic forcing.

Key takeaway from the research

• The research concluded that particulate emissions have the potential to alter the physical and dynamical properties of cloud systems and, can amplify rainfall events over orographic regions downwind of highly polluted urban areas.
• The study made use of data between 2001 and 2017, data with regards to rainfall rate, aerosol measurements called Aerosol Optical Depth (AOD), meteorological reanalysis fields such as pressure, temperature, and moisture content at different altitudes are used to compute the thermodynamic variable “moist static energy” and outgoing long-wave radiation from Indian region to explore high precipitation events on the foothills of the Himalayas.
• The team found a correlation between high precipitation events, high aerosol loading, and high Moist Static Energy (MSE) values (Moist static energy of an air mass includes the potential energy due to its height above the ground and the latent heat due to its moisture content).
• The findings also highlight the crucial role of the radiative effect of aerosol on high precipitation events over the Himalayan region.

Significance of Aerosol study in Indo-Gangetic Plain

• The results of the study indicate that aerosols can play a vital role in exciting high precipitation (HP) events over the Himalayas during the monsoon season.
• The aerosols, including chemistry, are essential to consider when forecasting HP events over the Himalayan region in regional modelling studies.

Impact of Aerosols

• The aerosols can influence climate by scattering light and changing Earth’s reflectivity and they can also alter the climate via clouds.
• Natural aerosols (sulfates, sea salt or ammonium salt) are the most common condensation nuclei in pristine environments.
• It forms the brighter clouds which block the sunlight from reaching Earth’s surface and this cloud albedo effect may have a big impact on the climate.
• The aerosol can influence precipitation by either modifying cloud microphysical processes through aerosol activation, or by modifying local thermodynamical profile, facilitating an on-site impact on clouds overlapping with the aerosol population.