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Quest for Accurate Weather Prediction
Fourteen cyclones since 2004, thousands of casualties, coastal flooding and torrential rainfall — Tamil Nadu has weathered many a storm in recent years. Though the State Government, Regional Meteorological Centre (RMC) and the India Meteorological Department (IMD) have been chalking out mitigation strategies, an infrastructure upgrade is the need of the hour. By Priya Chadha
On December 30, 2021, the weather bulletin issued at noon in Chennai, predicted ‘light-to-moderate’ showers in some areas of the city. An alert issued a little later again warned that there would light-to-moderate rain at isolated places in Chennai and nearby districts for one or two hours. However, by the time an ‘orange alert’ was sounded, there was a heavy downpour in Chennai and three other districts, inundating most areas and leading to gridlocks. There was loss of property and human lives. Apparently, two of the three radars had not been working since November 6, 2021, and as per a report, the Regional Meteorological Centre (RMC) and the Indian Meteorological Department (IMD) had been issuing conflicting predictions.
The state government relies on IMD for any weather-related information. But the department’s predictions have not been so accurate of late, and its failure to do so is costing the state dear as it is unable to put in pre-emptive efforts to save lives.
Technology upgrade is the need of the hour as in such a situation, not only is normal life crippled, but health services are also affected.
An automated weather station
On plans to set up a new weather station, Dr. Mrutyunjay Mohap-
atra, Director General of Meteorology, India Meteorological
Department, said that like other states, Tamil Nadu too wants to improve its early warning system. “For instance, if we issue a warning, some action has to be taken, and to act as per the warning, a decent support system is required by districts, tehsils or blocks concerned. In addition to our automated stations, states are also establishing their own automated weather stations, which is why the Tamil Nadu government, too, wants to set up a similar weather station,” he said.
The automated weather station will be an observatory station, and will automatically record temperature, pressure, rainfall, etc. Mohapatra added, “IMD issues the forecast. No separate prediction is issued by Tamil Nadu. All our data is stored in GIS now. It is a collaborative work between IMD and the Tamil Nadu government. As per our guidance, we are working together and there is no separate meteorological facility. It will be augmented by setting up a few observatories by the Tamil Nadu government like any other government is doing. For
instance, Andhra Pradesh, Bihar, Odisha, Kerala and Karnataka are also working on it. So, if you go to smaller areas for forecast, we need more observations, which is why IMD is supported by the states concerned.”
Current infrastructure
“We have around 735 automated weather stations across the country. Then, there are 570 manned observatories, and 1,350 automated rain gauges. And, this number will keep going up. For the purpose, respective state governments are purchasing some equipment, but the cost of these cannot be commented upon,” Mohapatra said.
Referring to inaccurate predictions in Chennai on November 7 and December 30, 2021, he said a forecast cannot be 100% accurate always. “Over the years, if you look at the forecast accuracy of IMD, heavy rainfall warning has improved by 40% in the past five years. At present, we can predict heavy rainfall 20 hours in advance with 75% accuracy. Forecast accuracy is inaccurate worldwide, not only in India. Our target is that by the next five years, our forecast accuracy should improve by 10-15%.”
When asked about the weather station, Dr. S. Balachan-
dran, DDGM, Head, RMC
Chennai, said the project was
part of their expansion plan. On the inaccurate predictions, the official said an error-free forecast is not always possible. “At present, we have 75 automatic rain gauges and 35 automated weather stations.”
Sharing his views, Nagaraj, MSSRF, said that for predictions to be precise, the equipment at weather stations needs to be updated. He also highlighted the poor drainage system plaguing the state for long: “The Cooum river has become highly polluted. Flooding has made its condition even worse.”
Data collection
A lot of data is sent to Numerical Weather Prediction (NWP) models for analysis. Observations are made round the clock in three dimensions. Observatories, which are under the surface of the earth, take measurements. Also, balloons and sensors are used to generate upper air data by tracking with radars. There are, at present, 33 radars for weather in the country. There are also two satellites — INSAT 3D and INSAT 3DR. In addition, international satellites are also used for the purpose of collecting data.
Western Ghats block most rain-bearing clouds
The northeast monsoon is responsible for most of the rainfall in the state as winds and rain-bearing clouds come from the Bay of Bengal, which ensures good rain activity over Tamil Nadu. On the other hand, the southwest monsoon has a minimal role to play in the state’s rain pattern. About 48% of the annual rainfall is received during the northeast monsoon from October to December. Only the Nilgiri areas get rain from the southwest monsoon as winds are obstructed by the Western Ghats that dominate the entire western border with Kerala, effectively blocking much of the rain-bearing clouds from entering the state. The eastern parts are fertile coastal plains. The northern parts are a mix of hills and plains. The central and the south-central regions are arid plains.
CM’s letter to the Centre
Following IMD’s alleged failure in warning the authorities about the heavy showers that lashed Chennai, Tamil Nadu Chief Minister M.K. Stalin wrote to Union Home Minister Amit Shah, urging the Centre to take steps to rectify some lapses on part of the regional wing of the IMD in predicting rainfall.
Stalin pointed at the “need for making additional investments in advanced weather prediction mechanisms and upgradation of technology being used in IMCs (Indian Meteorological Centres).”
He also urged the Centre to enhance the capacity of the weather forecast center in Chennai to enable it to make predictions in high alert situations and to inform the state government well in time.
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