Cyclone Michaung | ‘Expect droughts and floods to become more extreme whenever they occur’

People wading through a flooded beach after heavy rainfall in Chennai in 2021. The current city flood is Chennai's third in eight years. (Photo by P. Ravikumar/Reuters)

Battered by Cyclone Michaung, Chennai is grappling with its third major flood in eight years. It highlights the growing vulnerability of India’s metropolitan cities to excessive rainfall and sudden flooding. Recognising this critical issue, the Government of India has now taken a significant step by approving the first-ever urban flood mitigation project for Chennai. The project, named Integrated Urban Flood Management activities for Chennai Basin Project, has been allocated a budget of Rs 561.29 crore, including Rs 500 crore as Central assistance. This initiative marks a crucial first step towards making Chennai more resilient against future flood events. It will also help develop a broader framework for urban flood management.

To understand the impact of climate change on India’s weather and unravel the country’s vulnerability to extreme weather events, we turned to Dr Akshay Deoras, research scientist at the National Centre for Atmospheric Science & Department of Meteorology, University of Reading, UK, with over 15 years of experience in weather forecasting for the Indian subcontinent.

We know that climate change is changing weather patterns around the world. But what is it that makes India more susceptible to extreme weather events?

India’s large population (and high population density in some parts) increases its vulnerability to extreme weather events. On top of that, weather forecasts and warnings still do not reach each person in the country, and those having access to warnings, often don’t know how to respond to them.

Even the response in a state is different for different events. For example, states along the east coast have managed to save lives from deadly tropical cyclones, but that’s not true for heatwaves. That apart, we are seeing an increasing role of illegal construction activities in intensifying the impact of certain extreme weather events such as floods in hilly states.

What specific extreme weather is likely to become more common in India in the coming years?

Climate projections generally indicate an increase in the average monsoon rainfall over India in the future. This, however, comes with a twist. The variability of monsoon rainfall is also expected to increase, which means that we can expect droughts and floods to become more extreme whenever they occur. Besides rainfall, the probability, frequency, and duration of heatwaves are also expected to increase in the future.

Does the increase in frequency and duration of heatwaves make the wet bulb index a bigger concern for the country?

The wet-bulb temperature combines the air temperature (which a standard thermometer measures) with humidity, giving a better measure of heat stress on human beings.

It is well-known that humidity makes us feel even hotter and disrupts how our body sweats and cools down. Conventional indicators of heatwaves, which are still in practice, ignore the role of humidity. For example, if the air temperature at a location is 35 degrees Celsius and the relative humidity is just 30 percent, the temperature that we feel (known as the heat index) will be 34 degrees Celsius. If the relative humidity increases to 60 percent, then the heat index will increase to around 45 degrees Celsius.

Current heat action plans in different parts of the country ignore the humidity factor. Heatwaves occurring during March to May are generally not associated with high humidity, so these heat action plans can be effective. However, heatwaves occurring during June or monsoon breaks are associated with high humidity, and heat action plans might not work in such cases.

The 2023 southwest monsoon withdrew from India in October. How normal or abnormal would you describe this year’s summer rain season?

This year’s southwest monsoon season was a rollercoaster. Seasonal rainfall across the country was below normal, with large rainfall deficits in eastern, northeastern, southern, and central parts.

While active and break spells are a normal feature of a monsoon season, the extended break we saw during August was astonishing. India witnessed the driest and warmest August on record since 1901. Nearly all districts in the western half of the country received scanty rainfall in that month, and states such as Gujarat, Kerala, Rajasthan, and Karnataka recorded rainfall deficits exceeding -70 percent. The damaging floods and humongous rainfall in parts of Uttarakhand and Himachal Pradesh during July and August were equally astonishing.

Lately, the IMD has been criticised for inaccurate seasonal forecasts and short-range ones. Are they getting it wrong or is making an accurate forecast getting more difficult in tropical countries due to climate change?

Forecasting the weather in the tropics has always been a challenging job. There is so much thunderstorm activity on many days in a year, which are localised or widespread in nature. Predicting the exact location of these storms and rainfall from them is a challenge.

The monsoon is a big system and is affected by global factors, so accurately predicting monsoon rainfall is another challenge. Thankfully, the performance of weather prediction models has improved a lot compared to what it used to be several years ago. We also have a good network of satellites and doppler weather radars that enhance the surveillance of the developing weather. So if a skilled meteorologist uses these products and shares a lucid forecast on a real-time basis with stakeholders, there shouldn't be a problem. The real problem starts when either the forecast is ambiguous or is not disseminated to the desired level. On top of that, climate change also makes it a challenge to predict the magnitude of rainfall during extreme weather events.

Dr Akshay Deoras.

So, are we asking the right questions with regards to climate change and extreme weather events?

It is good to see that climate change and extreme weather events are being discussed by legislatures in India. However, we see that weather anomalies (e.g., a monsoon flood) are incorrectly linked to extreme weather events and climate change. This can create panic and deviate action plans. It is therefore important to understand the science of climate change and its role in modulating extreme weather events.

The science is clear that global warming is fuelling extreme weather events, so we must limit global warming at any cost. We also need to ask more questions on reducing emissions, especially on the feasibility and efficacy of action plans. Furthermore, we need to ask what lessons have been learnt from extreme weather events witnessed till date.

Would being net-zero reverse extreme weather events in the near future?

We know that global warming will be restricted in a net-zero world, so that should prevent a further intensification of extreme weather events. However, it is not known yet if extreme weather events would be reversed in such a scenario. In fact, climate scientists are working on understanding how extreme weather events would evolve in a net-zero world.