Why the new ‘normal’ for rainfall calculation may be problematic for India‘s farmers

The value for ‘normal’ rainfall decreased by 12 millimetres, according to India Meteorological Department’s new standards

By Akshit Sangomla
Published: Friday 03 June 2022

It has been predicted that India will have a ‘normal’ monsoon in 2022, even as the values for ‘normal’ rainfall have changed by the India Meteorological Department (IMD).

This has created a confusing situation for the farmers of the country because even if the volume of rainfall is as low as last year’s, it will be officially treated as normal. The lived reality of the farmers will remain the same, despite a better monsoon on record.

The long-period average (LPA) rainfall that is used as the standard for ‘normal’ precipitation, was earlier calculated as the average of rainfall from 1961-2010. From this year, it is being calculated for the period 1971-2020. The actual value for ‘normal’ has decreased by 12 millimetres. 

On May 31, 2022, IMD forecast a normal monsoon for the year 2022 — 103 per cent of LPA. The prediction also accomodated a 33 per cent climatological probability of a below-normal and deficient monsoon. 

According to the forecast, India may receive 894.7 mm rainfall in the current monsoon season. If the earlier LPA was considered, this would be 101.6 per cent of the LPA. 

This would have been considered as a normal monsoon still, as per IMD’s definition (96-104 per cent of LPA), but the situation becomes different when individual regions are considered. 

For some regions, the volume of rainfall that would be categorised as ‘deficient’ till last year, will be recorded as ‘normal’ this year because of this shift.

For western Uttar Pradesh, the lower end of the new normal monsoon rainfall is 671.3 mm, according to IMD. The earlier normal value was 721.3 mm. If there is 550 mm of rainfall in the region this year, for instance, there would have been a deficient monsoon (23.8 per cent less rains than the normal) in 2021. 

With the new normal value, it would be a normal monsoon for the region (18 per cent less rains than the normal). 

The difference for western UP becomes even more stark when annual rainfall is considered, since the decrease in annual normal rainfall for the region is in the range of 50-90.1 mm. 

This would also lead to a change in the short-term forecasts issued by IMD. The variation, in turn, will lead to problems for farmers who are dependent on the forecasts and the advisories issued by local agricultural departments for sowing their crops. 

It will also lead to an increase in complaints from them regarding wrong rainfall forecasts issued by IMD — already a raging issue among the farmers across the country.  

On April 14, IMD had announced the new country-wide normal rainfall for the southwest monsoon season, along with a new normal for annual rainfall.

Both monsoon and annual normal rainfall have decreased, which means that there was less rainfall from 1971-2020 than from 196102010. The weather agency attributed this decrease to a decadal pattern of decreasing rainfall over India which began in the 1970s. 

The decrease in normal rainfall in different regions of the country is not uniform: There is an increase in some regions while there is a drastic decrease in others. 

Monsoon rainfall in Nagaland, Manipur, Mizoram and Tripura, for instance, showed the highest decrease in normal rainfall value in the range of 90-121.5 mm, according to IMD. 

In the case of annual normal rainfall, the northeastern states of Arunachal Pradesh, Nagaland, Manipur, Mizoram and Tripura showed a decrease in normal rainfall in the range of 90-152.9 mm, it added.

In Himachal Pradesh, Uttar Pradesh, Sikkim and north Bengal the decrease was in the range of 50-90.1 mm, the national weather forecast agency noted.

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