Imperial College study finds climate change raised Cyclone Arnab damage by 33 per cent

What the study found

Researchers at Imperial College London used the Imperial College Storm Model, or IRIS, to examine how global warming affected Cyclone Arnab's intensity, rainfall and economic impact, Kashmir Convener reported on 5 November. The study estimates that about 25 per cent of the cyclone's total economic losses were attributable to human-induced global warming, compared with the damage that would have occurred under pre-industrial climate conditions. Overall losses rose 33 per cent against that baseline.

The analysis found that climate change increased Arnab's maximum wind speed by 9.3 kmph, about 5 per cent, and its eyewall rainfall rate by 1.1 mm per hour, about 11 per cent. It also raised the likelihood of a cyclone of similar intensity by about 19 per cent compared with pre-industrial conditions. The likelihood of similarly intense rainfall events rose by around 18 per cent, and the estimated return period for such rainfall fell from 16.7 years to 14.2 years.

Cyclone Arnab was a Category 4 storm with a lifetime maximum wind speed of 220 kmph over the Bay of Bengal. At landfall it was equivalent to a Category 3 cyclone, with winds of around 202 kmph.

Future warming and the damage estimate

The researchers also examined a future warming scenario of 2.6 degrees Celsius above pre-industrial levels. Under that scenario, a cyclone similar to Arnab could have maximum wind speeds 8 per cent higher and eyewall rainfall 22 per cent greater, and could cause 56 per cent more economic damage than under pre-industrial conditions.

The economic assessment used wind-field estimates, damage functions and asset exposure data, while accounting for uncertainties in wind speeds, asset values and damage calculations. The research is part of the Climate Damage Tracker initiative, which aims to provide rapid estimates of how climate change influences damage from extreme weather events by combining climate attribution with socio-economic impact data.

What the authors say

Dr Nathan Sparks, a researcher in Tropical Cyclone Risk Modelling at Imperial College London's Department of Physics, said the findings highlighted the immediate economic consequences of climate change for coastal communities. He said stronger winds and increased rainfall could result in greater destruction of homes and infrastructure, crop losses and damage to livelihoods.

Prof Ralf Toumi, Director of the Grantham Institute, said the research demonstrated the real-world consequences of continued fossil fuel emissions during major storms. He noted that while the overall number of tropical cyclones globally remained relatively stable, the storms that formed were becoming more dangerous and powerful.

Why the number matters

Attribution science compares the climate that occurred with a modelled version of the same event without human-caused emissions, according to PreventionWeb. Scientists assess whether an individual heatwave, flood, wildfire, storm or drought was made more likely, more severe, and by how much. The Imperial study applies that method to a single storm and adds an estimate of the economic damage tied to warming.

The findings come amid a year of widespread extreme weather in India. The Centre for Science and Environment and Down To Earth reported on 4 November that extreme weather occurred on 251 of the 273 days from 1 January to 30 September, nearly 92 per cent of the period.