The India Meteorological Department (IMD) has changed the languages and also re-defined terms that are not scientifically precise in weather forecasting.
In this regard, IMD has issued official notification to do away with outdated language to avoid communication gap with the civil administration so they can be more realistic in case of upcoming weather events.
IMD has reviewed the terminology and factors determining each of these terms based on supporting observational data.
Following are the changes
Classification all-India rainfall into five categories
- Normal: ± 10 percent of the long period average (lpa).
- Below normal: Rainfall lower than 10 percent below average of the lpa.
- Above normal: Rainfall greater than 10 percent above average of the lpa.
- Deficient year: Rainfall deficit between 10 and 20 percent up to 40 percent of India’s spatial area.
- Large deficient year: Rainfall deficit of over 10 percent across more than 40 percent of India’s area.
IMD New standardized key terms
- Heat wave: Temperatures greater than 4.5 Degrees Celsius above usual temperatures for the region.
- Severe heat wave: Temperatures greater than or equal to 47 Degrees Celsius.
- Cold wave: Temperatures less than 4.5 Degrees Celsius below usual temperatures for the region.
- Severe cold wave: Minimum temperature is 2 Degrees Celsius or lower.
Criteria to classify seasonal rainfall
- The rules have been changed to classify seasonal rainfall. IMD has introduced 6 new categories replacing old four rainfall categories (excess, normal, deficient and scanty). New categories are
- Large excess: 60 per cent and above.
- Excess: between 20 per cent and 59 per cent.
- Normal: minus 19 per cent to plus 19 per cent;
- Deficient: minus 20 per cent to minus 59 per cent.
- Large deficient: below 60 per cent
- No Rain: 0 per cent.