Guwahati: Air pollution may be quietly reshaping rainfall patterns in Mawsynram—the world’s wettest place—according to a new scientific study that links rising aerosol pollution to a steady decline in rainfall over the past decade.
The study, published in the Journal of the Indian Society of Remote Sensing, was conducted by Mamta Devi, Sumit Kumar Mishra, Kartika Pandey, Supreet Kaur, Anikender Kumar, Vijay Kumar Soni, Amarendra Singh, and Atul Kumar Srivastava.
Using satellite observations and ground-based rainfall data from 2014 to 2023, the researchers examined how changes in atmospheric aerosols are influencing clouds and precipitation over the Meghalaya Plateau.
Aerosols are tiny airborne particles released from sources such as biomass burning, vehicle emissions, fossil fuel use, and pollution transported from distant regions like the Indo-Gangetic Plain.
While invisible to the naked eye, these particles play a critical role in cloud formation and rainfall by acting as nuclei around which cloud droplets form.
The study found that aerosol levels over Mawsynram, measured through aerosol optical depth (AOD), increased by about 14.6 percent over the last decade. During the same period, annual rainfall declined by nearly 14 percent, falling from 10,235 mm in 2014 to 8,838 mm in 2023.
Statistical analysis revealed a strong and significant inverse relationship between pollution and rainfall. “A notable decline in regional annual rainfall, with a significant negative correlation (r = −0.615) with aerosol optical depth, underscores the intricate interactions between aerosols and local climatic patterns,” the authors note.
According to the researchers, higher concentrations of fine aerosols lead to the formation of smaller cloud droplets, which are less efficient at merging into larger raindrops. This delays or suppresses rainfall, even in an area known for extreme precipitation.
“Higher fine-mode aerosol concentrations may inhibit cloud formation by delaying droplet coalescence,” the study explains. This phenomenon—known as the aerosol indirect effect—can reduce rainfall efficiency even in moisture-rich regions like Meghalaya.
Satellite data showed that while cloud cover remains substantial, the effective size of cloud droplets has gradually decreased, making clouds less likely to produce rain.
The impact of aerosols was most pronounced during the pre-monsoon and winter seasons, when pollution levels were highest. Aerosol concentrations increased steadily by about 0.007 per year, with fine particles becoming increasingly dominant in the atmosphere.
These seasons coincide with increased biomass burning, reduced rainfall that limits the natural cleansing of the atmosphere, and long-range transport of pollution—all factors that intensify aerosol buildup over the region.
Beyond rainfall changes, the study found that aerosols are also altering Mawsynram’s energy balance. Atmospheric heating rates increased over the decade, rising from 0.4 to 0.6 K per day in winter and from 0.5 to 0.7 K per day during the pre-monsoon.
At the same time, less sunlight is reaching the ground—a process known as surface dimming—while more heat is retained in the atmosphere. This combination can further disrupt cloud formation and local circulation patterns.
“These results highlight the complexity of aerosol–cloud–rainfall interactions in a climatically sensitive region like Mawsynram,” the authors write, noting that such processes are often underestimated in climate models.
Mawsynram is globally significant as the wettest place on Earth and a critical indicator of monsoon behaviour in Northeast India. The findings suggest that even extreme rainfall regions are not immune to pollution-driven climate disruptions.
The authors argue that understanding these aerosol-driven changes is essential not only for regional water security but also for improving global climate and monsoon models. What is unfolding over Mawsynram, they note, offers valuable insights into how air pollution can subtly but persistently reshape rainfall patterns worldwide.
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