How normal were the rains? IMD chief wants to study more factors to know

With climate change causing changes in annual precipitation and ocean temperature levels, these parameters need to be included in forecasting system: KJ Ramesh

By Akshit Sangomla
Published: Monday 26 November 2018
Extreme weather events
The global rainfall data over the past century shows an alarming trend. Credit: Getty Images The global rainfall data over the past century shows an alarming trend. Credit: Getty Images

The distribution of rainfall, especially during the monsoon, is a major concern in India as most of its people still depend on rain-fed agriculture. But how to gauge whether that distribution is normal? Until now the government has depended on the volume of rainfall in districts and their deviation from normalcy. But India's weather chief thinks more parameters need to be factored in.

Water levels in reservoirs after the monsoon and the acreade of rain-fed crops in districts can be two such factors, said K J Ramesh, the director general of India Meteorological Department (IMD). 

According to him, global rainfall data for over the last century shows an alarming trend: "The number of rainy days are decreasing while intense rainfall events of 10-15 cm/day are increasing. This means that more amount of water is pouring down in lesser time. For example, globally, 50 per cent of annual precipitation (rain, snow and ice) is received in just 11 days,” Ramesh said at the pre-conference of parties' national media briefing conducted by non-profit Centre for Science and Environment (CSE) in New Delhi on November 23.

This trend is visible in India as well, with high rainfall events (more than 10cm/day) increasing and low rainfall events (less than 5cm/day) falling. The pattern is similar in the data of decades of the past century. In recent decades, extremely heavy rainfall events have risen, Ramesh falling. Northwestern and Peninsular India have been particularly vulnerable.

When such heavy rainfall events are stretched over a few days and combined with certain geographies, natural degradation and bad water management, they can result in catastrophes such as the Kerala floods in August 2018, which claimed close to 500 lives and caused damages of anywhere between Rs 30,000-40,000 crore. Coastal areas are particularly vulnerable to such deluges, with sea level rise also affecting them in the long run as a result of climate change.

Cyclones are another manifestation of extreme weather that are likely to become more deadlier due to ocean surface warming - another impact of climate change. India is exposed to 10 per cent of the world’s cyclones, according to the National Cyclone Mitigation Project. Over the years, India had become better at predicting cyclones and minimising damage caused by them. But now, cyclones are becoming increasingly unpredictable, especially in matters of intensification. When these enormous storm systems find warm pockets of ocean water, they intensify rapidly, making them difficult to be forecasted with accuracy. This is what happened in the case of Cyclone Ockhi last year which had claimed over 200 lives in Tamil Nadu and Kerala. It had picked up water vapour over the sea between Sri Lanka and Kanyakumari and rapidly intensified from a depression into a cyclone in a matter of 13 hours. “It was the first cyclone where such rapid intensification in a short span of time has ever been observed”, said Ramesh. The IMD also observed a similar phenomenon at play in two of the recent cyclones that hit the Indian mainland this year - very severe Cyclone Titli and severe Cyclone Gaja. Both caused considerable damage in Odisha and Tamil Nadu respectively.

But IMD is already at work to remedy this situation. It is continuously revising its forecasting models and procedures to integrate more parameters that can affect the creation and propagation of extreme weather events. It is now using an ocean-atmosphere coupled framework for forecasting cyclones and other extreme events. This would mean that apart from atmospheric parameters, ocean surface warming will also be accounted for in the forecasting process. Cyclones Titli, Luban and Gaja were the first cyclones to be forecasted using this model. The IMD is also working closely with the National Disaster Management Authority (NDMA) to improve the early warning systems for various disasters especially along the Indian coastline. It has started off with an advanced tsunami warning system for the Andaman and Nicobar islands. The IMD is also working on a model to monitor the behaviour of reservoir catchments in real time during heavy rainfall episodes like what happened in Kerala in August.

“During the floods in Kerala and earlier in the Northeast, an increased surface run-off was observed. Natural degradation and unbridled development in these regions has led to narrowing down of natural drainage. This is a major cause of flooding, apart from the heavy rainfall events”, Ramesh said. Therefore these factors need to be taken into account when floods are monitored. 

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