Cause and effect | Beyond the headlines about Delhi's floods

The water level in the Yamuna on Thursday reached a record 208.66 metres, the highest since 1978, as heavy rainfall in north Indian states prompted neighbouring Haryana to release water from the Hathnikund Barrage.Parts of the Capital, including the Red Fort, were flooded by Friday, with thousands evacuated from affected areas.While the news caused alarm, and rightfully so, in most of its readers, there were also a few who, probably out of climate fatigue, asked, “Is Delhi getting flooded again?”“Flood alert for Delhi” has dominated headlines in the monsoon season for the last couple of years, with the city having received excess rainfall in 2022 (286.3mm), 2021 (507.1mm) and 2020 (236.9mm).But what is unusual this year, is the amount of rain the city has received over the short duration.In the first nine days of July, when incessant rain brought most of north India to its knees (in knee-deep water), the city received 46.35% of the total rainfall it receives through the four-month season.Among other states, Himachal Pradesh was the worst affected with over 80 dead, several highways washed away, key bridges broken, and rivers in spate.At least 100 people died across the country in rain-related incidents.And this may only be the beginning. Scientists have for long warned that the climate crisis is making extreme weather more frequent.The sixth assessment report (AR6) of the Intergovernmental Panel for Climate Change (IPCC) warned that summer and monsoon precipitation will increase and become more frequent, predicting a 20% surge in extreme rainfall events.Meteorologists said that the heavy rain last week was a result of an interaction between various weather systems.The ‘very heavy’ category rainfall was the consequence of monsoon winds interacting with a western disturbance, which triggered precipitation across much of northwest India. A western disturbance’s main characteristic is bringing rain to an area.“The ongoing spell of extremely heavy rains is due to the alignment of three weather systems, Western Disturbance over Western Himalayas, cyclonic circulation over northwestern plains, and Axis of Monsoon trough running across Indo-Gangetic Plains. This alignment is not happening for the first time and is the usual pattern during the Monsoon," Mahesh Palawat, vice-president, meteorology and climate change, Skymet Weather, said in an emailed statement.But, linkages with a warming planet are hard to miss. "Global warming-led changes in Monsoon patterns have made a difference. There has been a constant rise in both land and sea temperatures, which has increased the capacity of the air to hold moisture for a longer time. Thus, the role of climate change in the increasing extreme weather events in India has been strengthening with each passing year,” Palawat said in an email statement.A warmer atmosphere holds more moisture, which results in storms dumping more precipitation. A distinction to be made is: climate change by itself is not the cause of the storms increasing rainfall, but as the heat gets trapped in the atmosphere storms are becoming more frequent, hence bringing more rain.As a storm develops, water vapour is condensed into rain droplets and falls back to the surface as rain. As storms form in warmer, humid environments, the rainfall increases.“Warm air expands and cool air contracts. You can think of it as a balloon - when it’s heated the volume is going to get larger, so therefore it can hold more moisture,” Rodney Wynn, a meteorologist at the US National Weather Service, told AP.For every 1°C rise in temperature, the atmosphere holds approximately 7% more moisture, the IPCC report said.The global temperature has already increased by 1.1 degrees C over pre-industrial levels. “Heavy precipitation will generally become more frequent and more intense with additional global warming,” the IPCC warned.“Climate model projections show that the increase in water vapour leads to robust increases in precipitation extremes everywhere, with a magnitude that varies between 4% and 8% per degree Celsius of surface warming,” the report said.According to projections, at a warming of 4 degree Celsius relative to pre-industrial level, very rare – one in 10 or more years – heavy precipitation events would likely double, and 50-year events, triple.For coastal regions, changes in sea surface temperatures alter land-sea contrast, bringing more rain to areas on the coast."The projected larger SST increase near the coasts of East Asia and India can result in heavier rainfall near these coastal areas from tropical cyclones or torrential rains. The warming in the western Indian Ocean is associated with increases in moisture surges on the low-level monsoon westerlies towards the Indian subcontinent, which may lead to an increase in the occurrence of precipitation extremes over central India,” the report said.The increase in intensity of rain increases the frequency and magnitude of floods that exceed the “capacity of natural and artificial drainage systems”, the report said.Till Wednesday, at least seven states in north India had witnessed floods.And India isn’t alone.Torrential rain flooded parts of Japan, New York saw worse flooding than Hurricane Irene in 2011, while parts of China reeled from intense heatwave, there was extreme flooding in yet others. Mexico and Spain are witnessing heatwaves, while there is rare snowfall in South Africa. The Atlantic Ocean is experiencing its worst heatwave ever, the sea surface temperatures have jumped to 1.7°C above the 1951-1980 average.“...2023 has been a unique year. Global warming is making a significant contribution but there are some other factors as well. Firstly, El Nino has taken shape, which is amplifying global temperatures. Secondly, wildfires have been in three times larger areas, releasing three times of carbon into the atmosphere, and increasing greenhouse gases. Thirdly, North Atlantic Ocean is in a warmer phase. Fourth, the Arabian Sea has warmed unexceptionally since January, infusing more moisture over North-Northwest India. And lastly, the upper-level circulation pattern is also unusual, which forces local surface circulations, bringing rains like the one we are witnessing across north and central India,” said Dr Raghu Murtugudde, Earth System Scientist and Visiting Professor at IIT-Bombay.The weather extremes have come at a time the scientists are trying to define the Anthropocene, a new geological epoch borne out of humanity’s impact on the planet.The 4.6-billion-year history of Earth is divided by geologists in a hierarchical series on a time scale. Currently, Earth is in the Holocene epoch, which began 11,700 years ago as the last ice age ended.Anthropocene is a theoretical epoch which marks the point from which human impact has assumed prime influence over Earth’s geology and ecosystems.Scientists now believe that human activity has evicted the planet from the Holocene and sharp surges in greenhouse gas, microplastic pollution, invasive species, and radioactive traces have added up – marking the first time in Earth’s history that a single species radically changed the planet's morphology, chemistry and biology.

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