Dr Mrutyunjay Mohapatra, director general of the IMD, spoke to The Indian Express about climate change and weather forecasting; the advances that have been made, and the challenges that remain. Edited excerpts below.
On the impression that developed nations forecast weather more accurately:
India falls in the tropical region; extra-tropical regions are in the middle and higher latitudes where most of Europe, northern United States, and Canada are located. The weather in the tropical region is different from that of the extra-tropical regions. Cyclones, the monsoon, thunderstorms are characteristic of tropical weather systems. Tropical weather is associated with convective forces of the atmosphere. The intense heating of the Earth’s surface plays a dominant role in the genesis, evolution, characteristics, propagation, and movement of the weather in these areas. Extra-tropical weather systems are more systematic and periodic, and therefore, in general, easier to predict. In comparison, the weather in the tropical zones is a little less predictable.
Having said that, our weather forecasts are as good as anyone else’s. There has been tremendous improvement in the forecasting of tropical cyclones in the last 10 years; our pin-pointed forecasts is something that other countries are trying to emulate. Similarly, the accuracy of monsoon forecasts, especially of extreme rainfall events, has increased from about 60 per cent 10 years ago to over 80 per cent now.
Even for thunderstorms, the potential zone of occurrence is being predicted five days in advance. These are not easy to predict because they are localised in about a 1-10-km area, and last barely half an hour to three hours. The specific location is predicted at least three hours in advance. Here again, our accuracy is among the best in the world.
Lightning is a major killer during thunderstorms. India is one of the very few countries that provide lightning forecasts. This is constantly being improved. We are able to identify potential hotspots 14 days in advance, and a lightning warning is issued every three hours on the day of the occurrence from over 1,000 stations across the country. We have an app called Damini, which provides location-specific information about the occurrence of lightning during the past 5, 10, and 15 minutes, and a lightning forecast for the next 45 minutes.
A large number of deaths used to happen because of heat waves until a few years ago. Because of an accurate forecasting system, and effective communication and dissemination of information, the loss of lives due to heat waves has come down to single digits now. We are also working on cold wave predictions.
On visible trends in extreme weather events, and the ability to predict them:
Globally, temperatures have risen by about 1.2 degrees Celsius compared to a 100 years ago. Over India, the rise has been about 0.6 degrees Celsius. The rise has been more in the northern, central, and eastern parts, and less over peninsular India.
This rise in temperature has an impact on extreme weather events. It’s getting hotter not just on the surface, but also in the troposphere, increasing its water-holding capacity. Studies show that with a rise of 1 degree Celsius, moisture-holding capacity increases by about 7 per cent. If the atmosphere has the capacity to hold more moisture, it will have the capacity to cause more rainfall.
So, the probability of occurrence of heavy rainfall has increased. Studies also show an increase in the frequency of heavy rainfall events. These are events when 24-hour accumulative rainfall on a particular day is more than 15 cm. Such events are increasing over the tropical belt as a whole, including in India. This trend is more evident in Maharashtra, Gujarat, Odisha, and West Bengal.
On rainfall days, heat waves, cyclones:
On average, the number of light rainfall and moderate rainfall days are decreasing, while the number of extreme rainfall events are increasing. But total rainfall during the monsoon season has remained largely unchanged. This means when it rains, it rains heavily, and when it doesn’t rain, it doesn’t rain at all.
This trend is quite significant across the country’s central belt. A decrease in rainfall activity has been observed over Kerala and Jharkhand and adjoining areas, but an increase in West Bengal, western Uttar Pradesh, and parts of Karnataka.
When you consider heat waves, the increase is more in the central and northern parts of India. Cold wave conditions are likely to decrease because of the increase in temperature. Lightning also shows an increasing trend. There has been an increase in thunderstorms because of the rise in the moisture content in the atmosphere due to temperature increase.
The intensity of cyclones in the Bay of Bengal does not show any significant change, but Arabian Sea cyclones are showing an increase in intensity.
On projections of weather for the future:
In the business-as-usual scenario, the temperature can rise as high as 4 to 5 degrees Celsius by the end of this century. But this will most likely not be the case in view of our efforts to reduce emissions of greenhouse gases. Even so, heatwave conditions — area, duration, and frequency — are likely to increase.
Monsoon rainfall is projected to increase, and so are events of extreme rainfall. Rainstorm events, which are related to floods, are also expected to increase.
In general, extreme events will become more frequent and more intense, going by the current projections.
As you go towards extremes, their occurrence becomes very rare, and as the event becomes rare, the probability of prediction decreases gradually. For example, we did predict the occurrence of the recent wet spell in Maharashtra and the Konkan, but if we want a granular prediction, say over a small area of a city or a town, then there are limitations with current resources and technology. Same is the case if you want accurate quantitative rainfall forecasts, for example. We are trying to improve our capabilities, and there is an ongoing effort in Mumbai to provide very granular forecasts.
On what our weather forecasting system might be like 10 years from now:
We have three main objectives.
First, to ensure that no severe weather goes undetected and unpredicted. In the next five years, we will have augmented our observational system that will enable us to detect, and predict, every severe weather event. The idea is to enhance our capacities so that even small-scale events can be predicted at the granular level with longer lead times.
The second objective is to improve impact-based forecasts. As mentioned earlier, we are trying to have very realistic impact-based forecasts incorporating hazards, vulnerability and risk analysis, for four significant severe weather events — tropical cyclones, heavy rainfall, thunderstorms, and heatwaves. They result in major losses of life and property, and we hope to minimise the losses through effective forecasts.
The third objective is to make updated weather information available to everyone, every hour. For this, observation and communication systems have to be improved, mobile apps have to be developed.
On the IMD’s accountability for inaccurate weather forecasts:
As you focus on a smaller and smaller area, the uncertainty in predictions increases. But if you compare forecasts of 10 years ago with those of today, there has been tremendous improvement in the prediction of all weather events, including heavy rainfall. I am sure it will improve further. If you look at large-scale systems that cause widespread damage to life and property, they are being predicted fairly efficiently.
On the recent heatwave in Canada:
In heatwaves, there is a rise in temperature above normal up to about 5 degrees Celsius, so the human body cannot adjust to it. During this period, there was subsidence, that is downward movement of air because of high pressure. Warm wind was blowing from west to east. Subsidence means air is moving from the top level of the atmosphere downward, the warm air is devoid of any moisture, so it does not relate to any convective clouds and at the same time, the temperature increases.
Transcribed by Mehr Gill
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