Why Rising Temperature is Causing Long, Dry Periods and Short Spells of Downpour During Monsoons

Floods in Kerala. Courtesy PIB

Why is rain not evenly distributed through the season and why are there long, dry spells and a few days of heavy downpours? Writing in the Times of India of 21 June, Roxy Koll, a climate scientist at the Indian Institute of Tropical Meteorology, attributes it to climate change. He says rising temperatures increase moisture levels in the atmosphere. Warmer air holds more moisture – for a longer time. As a result, strong monsoon winds in the Bay of Bengal now carry a lot more moisture than ever and result in heavy rains that have caused devastating flooding in the Northeast and Bangladesh. Meghalaya’s Mawsynram, the world’s wettest place, recorded more than 1,000 mm of rain on 17 June, the highest June rainfall the Indian Meteorological Department has ever recorded for this station.

Koll says monsoon patterns have seen a shift over South Asia since the 1950s. The most significant change is that instead of moderate rains spread through the monsoon season, there are long dry periods interspersed with short spells of heavy rains since the moisture-holding capacity of the air has increased with global warming. So, when it rains all that moisture is dumped in a few hours or days. As a result, both droughts and floods occur across South Asia, and sometimes in the same season.

The total amount of rainfall is expected to increase by 7-10 percent for every 1°C rise in temperature. Extreme rainfall events are projected to increase over South Asia. It is the most vulnerable to climate change due to proximity to the rapidly warming Indian Ocean and the rapidly melting Himalayan glaciers.

Koll says the east coast of India and Bangladesh are particularly vulnerable since the sea-level rise in the north Bay of Bengal region is faster than any other region due to gradually sinking land. Storm surges are particularly large in the Bay of Bengal compared to the Arabian Sea. The combined effect of sea-level rise and storm surges leads to salt-water intrusion into agricultural land. It can also cause outbreaks of cholera.

There is a need to disaster-proof houses and farms and make them climate resilient. We need policies, Koll says, to redesign our cities and prepare rural areas for intensifying cyclones, floods and heatwaves.

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