Meghalaya experiences an alarming spike in extreme rainfall due to climate change

A recent study conducted by researchers across India, Bangladesh has revealed alarming trends in extreme one-day rainfall events in parts of India and Bangladesh, particularly in the northeastern regions including Meghalaya. Published in the Quarterly Journal of the Royal Meteorological Society, the study emphasizes a dramatic quadrupling of extreme rainfall events since 1979 due to the effects of climate change.

Climate change increases extreme monsoon floods

Lead author Abdullah Al Fahad, a NASA Goddard Space Flight Center assistant research scientist, highlighted the challenges posed by these events, stating that "the worst instances of extreme rainfall are already happening due to climate change."

Fahad told Ground Report "Due to climate change, the flood-causing extreme rainfall events over northeast India and Bangladesh have already quadrupled in the last 72 years and are projected to impact more areas in the coming decades".

He added, "In our attribution process, we found that warmer climatic conditions over the Bay of Bengal are primarily responsible for the flood-causing, one-day extreme rainfall events. Due to the warmer climate, the increased sea surface temperature of the Bay of Bengal causes more moisture to accumulate in the atmosphere. This moisture is then quickly carried inland by increased wind speeds, resulting in extreme rainfall events."

The study explains that extreme rainfall events, driven by strong moisture convergences near the Arakan Mountain and storm surges from the Bay of Bengal, are particularly prevalent during the monsoon months. These events often lead to landslides in hilly areas and disrupt local communities.

He said “Many studies focus on data from only one of these countries, which does not fully capture the scenario, given the close geographical relationship between the Meghalaya and Assam regions of India and northern Bangladesh. Both Bangladeshi and Indian policymakers must consider meteorological data from both countries when assessing the impact of climate change on local communities and devising strategies to mitigate disaster scenarios.”

Fahad further said, "We found that the locations most affected were primarily over Meghalaya and to its south in terms of frequency. Although the number of extreme rainfall events was not a direct factor for Assam, more severe floods are projected to increase due to more rain in the surrounding regions of Assam and Meghalaya".

"While the total rainfall in most of these regions is decreasing, our paper shows extreme rains are increasing," Dr Roxy Mathew Koll Climate Scientist at the Indian Institute of Tropical Meteorology Koll told Ground Report.

"Bangladesh and Northeast India face increasing flood risks due to extreme monsoon rains, exacerbated by dense populations. The rising rainfall intensity challenges weather forecasting models amid climate changes. Future projections indicate further escalation, necessitating long-term flood-proofing strategies. Targeting hotspots and ensuring flood resilience across vulnerable districts is crucial," emphasized Koll.

Northeast India faces irregular rains

In recent years, parts of northeastern India have faced rainfall deficits and irregular rain patterns, leading to longer dry spells. June 2022 saw extreme rainfall and flooding in the India-Bangladesh region, causing casualties and displacements, emphasizing the need for policymakers to consider regional meteorological data for disaster mitigation strategies.

Fahad added, "The increase in extreme rainfall events is due to the warmer sea surface temperatures caused by the rise in anthropogenic CO2 in the atmosphere. Additionally, deforestation and local infrastructure further exacerbate the impact of extreme rainfall events on local communities, as water is likely unable to flow downstream properly."

Various datasets such as IMD, APHRODITE, and ERA-5 consistently show a quadrupling of extreme events in western Meghalaya and northern Bangladesh during the monsoon season. These datasets attribute this increase to changes in lower-level jet streams, warmer sea surface temperatures, and shifts in moisture transport patterns, which lead to intensified moisture convergence and extreme rainfall events over the study region.

Climate change-induced warming and increased moisture transport are expected to worsen extreme rainfall in the future. The study projects a doubling of extreme one-day events annually by 2050-2079. Human activities like infrastructure development exacerbate flooding impacts, underlining the urgency for improved forecasting and early warning systems in vulnerable regions.

Seasonal monsoon rains come from Bay of Bengal's moisture carried by strong low-level winds to inland areas. Heavy rainfall results when this moisture meets local topography, lasting 1 to 5 days.

"Meghalaya receives rainfall from robust monsoon southerlies colliding with its east-west oriented mountains. The surge in heavy precipitation may stem from amplified monsoon winds and the resulting moisture convergence. Warming of the Bay of Bengal could also play a role. Such trends align with rising heavy precipitation in various regions. However, I have concerns about the reliability of rainfall data in the region," expressed M Rajeevan, former secretary of the Indian Ministry of Earth Sciences.

Meghalaya's fourfold summer increase, and links climate change

The research findings highlight a significant increase in extreme rainfall events over the past 72 years, particularly during the May to October monsoon season. They discovered a fourfold increase in summer monsoon extreme events in Meghalaya between 1979 and 2021, influenced by changes in low-level winds and warmer sea temperatures.

Fahad said, "Previous studies here focused only on heavy rainfall, using limited data and short timeframes. Our broad method used extensive data from multiple stations since the 1950s, clearly linking climate change to extreme rainfall."

The observed trends in extreme rainfall events over Meghalaya are linked to changes in atmospheric circulation and moisture content. The study identifies a strong relationship between extreme rainfall events and large-scale atmospheric circulation changes preceding the events, indicating dynamic influences. However, thermodynamic factors such as moisture transport and increased atmospheric moisture content also play significant roles in driving extreme rainfall changes.

Future climate projections based on CMIP6 models indicate a further increase in extreme rainfall events over the NEBI region, aligning with expected trends of intensified moisture transport, convergence, and warmer sea surface temperatures due to climate change. This underscores the urgent need for improved forecasting and early warning systems in vulnerable regions to mitigate flooding impacts.

The author of the study emphasized the importance of collaboration between Bangladesh and India as a crucial step in preparing for future disasters. While it may be challenging to reduce the number of extreme rainfall events, policymakers can still take steps to minimize their impact on local communities.

Local communities urgently need improved forecasting for extreme rainfall events and flooding. Policymakers need to engage closely with scientists to address this critical issue.

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