BL interview. Wait for IMD’s April forecast for more accuracy on monsoon: DG

There was a rise in temperature over northwest and central India (as per meteorological divisions), especially the Saurashtra and Kutch regions got maximum heating in terms of the day temperature. The temperature was about 8 degree Celcius above normal in Saurashtra.

The main reason for this abnormal increase in maximum temperature was due to an anti-cyclonic circulation formed over Gujarat, which led to subsidence of air (downward motion of air from upper to lower troposphere). As air moves downwards, it gets compressed and temperature rises.

In association with the anti-cyclonic circulation, as the wind rotates clockwise, the impact of heating in Gujarat was also felt in Punjab, Haryana, and Uttar Pradesh where the day temperature increased. But, the maximum during the day was in the range of 4-6 degrees Celcius above normal in north-west, whereas it was 8 degree in Saurashtra region.

Last year, the rise in temperature happened in March and it lasted for a longer period but this time, it took place in February. Also, it is for a short period now. The high temperature will continue till February 21 and thereafter, this anti-cyclonic circulation will become weak while moving towards the Arabian Sea. We do not expect that it will continue for a longer time.

As the anti-cyclonic circulation will not prevail, the temperature will fall after pretty fast over that area. You can expect a temporary fall in temperature but as the season progresses certainly there will be a rise in temperature because we are moving towards summer season.

India Meteorological Department (IMD) in collaboration with the Indian Council of Agricultural Research and the State’s agriculture department jointly issue the agromet advisory services every Tuesday and Friday. So, considering this higher temperature in northwestern and central India, farmers were advised what steps to take.

One of the major crops in north and central India during winter is wheat, which is likely to be affected (with such high temperatures if persisted for long). Higher temperature normally leads to early maturity of the crop, which means less yield. So, the objective should be to ensure that it is not impacted for which providing irrigation, providing mulch, etc., are necessary. So that there is no loss of water vapour from the soil and soil moisture is conserved. Secondly, agricultural practices also will be impacted because once you put irrigation your power requirement, etc., also will increase during this period.

Monsoon is a large scale process and it is a global process. It extends from Japan to America. But south Asia and south-east Asia are the major affected areas because of the monsoon. 70% to 90% rainfall occurs in India because of the monsoon. Therefore, this monsoon circulation or monsoon impact in terms of rainfall depends on many large scale processes. One of the large scale processes is El Nino and La Nina conditions - temperature distribution in East equatorial Pacific and West equatorial Pacific. So, if we look at now, it is the La Nina condition. But the La Nina condition is deteriorating and is moving towards the neutral conditions. So, in the coming months, we are expecting that it will be neutral conditions.

As you go towards the monsoon season, some models suggest that towards the second half (August-September) of the monsoon season, there could be El Nino conditions. And El Nino conditions are not good for the Indian monsoon as many deficient or normal rainfall years are associated with it. However, El Nino or La Nina is not the only parameter, which governs the Indian monsoon. So, there is also Indian Ocean Dipole (IOD), which is at present in neutral conditions. Forecasts are that the neutral condition of IOD will prevail till the monsoon season.

Regarding El Nino forecast, I want to say that the forecast of El Nino or La Nina, which is provided in the month of February, will have less accuracy because of the spring barriers etc. So, if the forecast is issued in the month of April, it becomes more accurate. So, therefore, what will be the final impact of whether it will be El Nino or La Nina, we should wait till the month of April when IMD issues a long-range forecast it takes into consideration all the large-scale processes.

Also read: Most global models see El Niño on the horizon, but unsure of intensity 

Any other climatic process that is going to impact monsoon?

The third largescale process, which also governs Indian monsoon, is the Eurasian snow cover (ESC).

This year, ESC has been less, it is quite low. The lower the snow cover, the better the rainfall activity, there is an inverse relationship. So, you have got a good favourable parameter here in terms of that, and whatever temperature you find a rise in temperature. So that rising temperature will help in melting of snow that snow cover will be less. This number has been less this year because of less number of Western Disturbances over the region.

Monsoon rainfall is impacted by large-scale inter-annual (year-to-year) variations and also large-scale intra-seasonal variations. El Nino or IOD are all inter-annual variations that we can estimate. But when the monsoon season advances during the season itself, there will be variation from day to day and that is called intra-seasonal variations.

The intra-seasonal variation is governed by the MJO (Madden-Julian Oscillation), which is one of the important factors during monsoon. When the season comes off, at that time the MJO forecast is taken into consideration. The MJO forecast can be only for next four weeks, so at this stage it cannot be issued for the monsoon season.