Over the previous ten years, there has been a roughly 50% increase in the accuracy of severe weather forecasts. At 88% accuracy, heatwaves can now be predicted 24 hours in advance.
Over the past two weeks, the India Meteorological Department (IMD) issued multiple heat wave alerts for different parts of the nation.
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Not even locations like Mumbai, whose coastal climate usually results in high moisture content lowering temperatures, escaped the heat. Nevertheless, compared to previous years at this time of year, Mumbai is said to have seen fewer cases of heat stroke. The better execution of heat wave action plans is credited with the reported decrease in cases.
In order for local governments to be better equipped to handle the extreme temperatures of this summer, the IMD—India’s official agency for meteorological observations, weather forecasting, and seismology—must provide them with timely, accurate, and informative forecasts.
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Thankfully, the agency’s heat wave predictions have improved dramatically over the last several years.
Science behind heat wave predictions:
An index or standard procedure for identifying a heat wave does not exist. Definitions also vary because the nature of a heat wave depends on the location and season. According to the National Disaster Management Authority (NDMA) of India, it is a time of exceptionally high temperatures—above the average maximum temperature—that have a negative impact on local residents by causing physiological stress and occasionally even death.
Before a situation is classified as a heat wave by the IMD, a few requirements must be met. These requirements are based on the highest temperature and the temperature deviation from normal at that specific weather station.
Usually, heat waves happen in the months before the monsoon. During this season, eight to ten of these days are typical, but over the previous ten years, there have been more frequent and prolonged heat waves. Thankfully, the dynamics of heat wave events are now better understood by meteorologists. For instance, we can now confirm that these are not regional occurrences.
“Heat waves are actually caused by large-scale atmospheric circulation processes, though local conditions like lack of rain and lack of soil moisture can support them,” explained MN Rajeevan, a meteorologist and former secretary to the earth sciences ministry.
According to Rajeevan, who also worked for the IMD for more than 20 years, “we can predict heat waves three to four days in advance with good confidence and we can also predict how long they will last if we know the basic dynamics of heat waves.”
How IMD forecasts heat waves:
IMD uses a vast network of surface observatories spread out across the nation to gather information on temperature, pressure, relative humidity, wind direction, and speed. They establish the parameters for heat waves in a given area by calculating the normal maximum temperature using historical daily maximum temperature data.
The forecast is then produced by IMD scientists using numerical weather prediction models that are fed initial conditions and observational data. Various models are employed to generate distinct forecast types, including seasonal, extended-range, and short-range forecasts. Rajeevan clarified, “The model can only predict the parameters conducive for a heat wave; it does not say that a heat wave will come.”
Accuracy of heat wave data:
Just in the last ten years, the forecast accuracy for all kinds of severe weather events has increased by roughly 50%. This is probably because there is now more data available, data processing techniques have improved, and more research has been done to understand the physical mechanisms underlying the phenomena.
In particular, heat waves can now be predicted with an accuracy of 88% 24 hours in advance. Rajeevan and his coauthor P. Rohini assessed how well different models predicted heat waves in India in a paper that was published in the journal Earth and Space Science last year.
The European Centre for Medium-Range Weather Forecasts (ECMWF) model performs exceptionally well in predicting heat waves in India, according to their research. The reason for this, the researchers reasoned, might be that the model’s mathematical formulas can forecast large-scale atmospheric forcing, a meteorological phenomenon linked to heat wave occurrences over India.
The daytime maximum temperature is the main parameter that IMD uses to track heat waves in the nation. This makes sense because most people are supposed to be awake and outside during the day, which makes it the period of time when we are most susceptible to severe weather. However, Rajeevan noted that heat can also have an impact on our bodies at night.
It’s also important to remember that measuring a heatwave requires more than just temperature. If the humidity is 70%, which is the case in many of the nation’s coastal regions, even 35 degrees can be harmful to humans.
Rajeevan strongly recommended that India start utilizing indices like the heat index, which is used in the US and provides “apparent temperature,” or what some weather apps refer to as “Feels like,” by combining air temperature and relative humidity.
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However, it might be necessary to modify even this for the physiology of India. “IMD is attempting to determine what our threshold is because our bodies react differently,” Rajeevan said. This is challenging because, even within our own population, there are significant differences in things like age and lifestyle.
Heat wave prediction in the future:
How much more accurate can heat wave forecasts get? According to a study that was published in Scientific Reports, machine learning models can be used in conjunction with numerical models to forecast maximum temperatures up to ten days in advance. It might not be possible to go beyond this. Rajeevan reminded him that there was such a thing as a predictability limit. “It is, after all, nature.”(Source: Hindustan Times).
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