Scope to improve local heavy rain forecasts: Mrutyunjay Mohapatra

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More than three months into the start of the southwest monsoon season (June-September), the pan-India average rainfall is above normal (5% above baseline), according to forecasts issued by the Meteorological Department. Indian (IMD). However, the distribution of rainfall has been uneven as central India and the southern peninsula receive excess rainfall, the eastern and northeastern regions have received insufficient rainfall. Mrutyunjay Mohapatra, dIMD Managing Director spoke with Sandip Das about the challenges faced in localized weather forecasting and the steps being taken to predict extreme weather events in rural and urban areas in advance through the deployment of Doppler radars and more vantage points.

Q: Although large parts of the country have received normal to above normal rainfall since June, the distribution of rainfall has been uneven?

As the IMD said at the start of the monsoon season, we expected the overall rainfall this year to be within the “normal” range and quantitatively, it was predicted that the cumulative rainfall would be 103% of baseline – long run average (LPA). So far, the cumulative monsoon rains have accounted for 105% of the LPA. However, the plains of the Ganges have become deficient and especially Uttar Pradesh which had received until now very insufficient rainfall. Rainfall deficit over Bihar, West Bengal and Jharkhand is now around 25% to 35%, while Uttar Pradesh’s deficit has been around 40% from baseline. However, we predicted that the Southern Peninsula region would receive deficit rains which did not happen as Kerala and Tamil Nadu have excess rains this season.

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Q: What are the factors that caused lack of rainfall in Uttar Pradesh, Bihar, West Bengal and Jharkhand this monsoon season?

Until June 15, rainfall was very poor across the country. From June 25, the monsoon rains accelerated. In June, there was no low pressure system triggering the rain. This has resulted in late monsoon arrivals in the central part of the country. This was not a typical monsoon advance. In July and August there were several consecutive low pressure systems. We saw 47 days of low pressure system versus 41 days of low pressure that we usually get from June to September which triggered more rainfall. All these low pressure systems developed over the northern Bay of Bengal near the Odisha coast moved northwest towards Madhya Pradesh, Chhattisgarh to Rajasthan. except for the recent low pressure system which moved across the Gangetic West Bengal.

The position of the monsoon trough which crosses Sri Ganganagar, Allahabad and Kolkata was located south of the normal position. This had brought rains to Gujarat, Rajasthan, Madhya Pradesh, Chhattisgarh and Odisha.

Q: How robust is our weather forecasting system and what are areas for improvement to accurately predict extreme weather events?

There has been a great improvement in the forecasting system, especially over the past five years or so. Quantitatively, there has been a 25-30% increase in the accuracy of forecasting severe weather events such as heavy rains, heat waves and thunderstorms compared to five years ago. Currently, forecasts for weather events we provide at the district level. We need to extend our weather forecasting to block and panchayat levels. Although block-level forecasting, IMD has started since 2021, the accuracy of the forecast needs to improve. When looking for location-specific heavy precipitation events, the accuracy was not high. At the 36 forecast levels provided by the IMD, the accuracy is around 75% to 80%.

Currently, we have 4500 meteorological observation stations in the country and the number of these observation stations is expected to increase significantly. We are setting up more automatic weather stations or automated rain gauges in collaboration with state governments. We will soon start using drones for weather forecasting for which we have requested expressions of interest from private entities.

Q: What are the plans to add Doppler radars to improve weather forecasting?

We started using Doppler radar since 2002 and in the following four years four radars were installed in Visakhapatnam, Machilipatnam, Chennai and Kolkata. Currently, we have 34 radars installed at various locations to provide advance information on extreme weather events. Ideally, we need more speed cameras. We plan to install 67 radars by 2025. Doppler radars of different frequencies – S-band, C-band and X-band – are used by IMD to track the movement of weather systems and cloud bands, and measure precipitation on its coverage area from 200 to 500 km. Doppler radars measure rainfall intensity and impact area in real time, which benefits farmers as well as local people.

We plan to install radars in urban areas to provide forecasts of urban flooding. Currently we have installed speed cameras in Chennai and Delhi, we are planning to install speed cameras in cities like Mumbai, Bengaluru, Pune, Bhubaneswar and Ahmedabad.

Q: On the impact of climate change on weather patterns and the increase in the number of dry spells?

Since 1970 due to the impact of climate change, the frequency of heavy rain events has been increasing in India as well as in all tropical countries. The duration of dry periods is longer and the duration of wet periods is less but more intense. Especially when there is a low pressure system, the intensity increases. While the mitigation strategy must be localized, the monsoon is a global phenomenon. We must opt ​​for severe weather warnings, especially heavy rain. We should increase the observation network so that all heavy precipitation events can be dedicated. We should go for high resolution modelling. Specific models for hilly areas and urban areas so that location-specific cold warnings are issued more accurately. We have a 10 petaflop IT system and the goal is to reach 30 petaflops in the next two to three years.

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