Explained: Taking stock of monsoon rainhttps://indianexpress.com/article/explained/india-monsoon-2019-forecast-weather-today-el-nino-taking-stock-of-monsoon-rain-5834844/

Explained: Taking stock of monsoon rain

How long will it take before it covers the entire country? Why is annual monsoon rainfall often below average? India’s Earth Sciences Secretary weighs in on monsoon forecasts and climate technology.

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New Delhi gets 95% of its monsoon rain in just 99 hours. (Express photo by Praveen Khanna)

How is the monsoon progressing this year and when will the entire country be covered?

After remaining very active until recently, the southwest monsoon has shifted to the Himalayan foothills and has caused widespread rainfall over the North and Northeast regions of the country. Reports of good rainfall have emerged from Uttar Pradesh, Bihar and even parts of Delhi. A fresh monsoon pulse is expected that will bring rainfall over Kerala, regions in the Southern Peninsula and along the West coast during this week. Though the monsoon will remain weak during the next few days, a low-pressure system that is likely to develop around July 25 will help in its revival. There is no need to worry as this fluctuation is part of the monsoon system.

However, the problem this season was due to a delayed start (onset) and its effects are still lingering. But our forecasts had indicated a delayed onset over Kerala and accordingly farmers, too, were intimated of take up sowing late. Overall, after the weakening of cyclone Vayu, which really slowed down the progress of the monsoon, the system picked up, and so far, the rainfall distribution has been good. The system is now picking up and monsoon is doing well so far. On Monday, the monsoon covered parts of Haryana and Punjab with a very small area of west Rajasthan now remaining. It will take another few days. The monsoon will cover the entire country before the end of July.

What are the notable variations observed in monsoons over the years?

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As per the rainfall data available for the last 150 years, there is no large variation in the total rainfall (all India), though there may be some higher variations observed at subdivisional levels. However, the southwest monsoon is a very robust phenomenon that undergoes largescale variabilities within the season. If one considers the annual all-India rainfall during the last 10 years, the realised rainfall over most of the years was less than 100 per cent of the LPA (long period average) and had varying negative departures. It was normal only for one or two years. This trend may continue for another few [years]. This could be because we are currently passing through a low monsoon epoch (a period of 30 years). But we have remained in the same epoch for many years now. This happens due to the variations controlled mainly by the oceans, which are largescale variations and importantly for the monsoon, variations realised from the Pacific and Atlantic Oceans. Ideally, we should have shifted from this low monsoon epoch to the positive epoch about 10 to 15 years ago but that has not happened yet. Scientists are still investigating the causes for this prolonged stay in this low phase. This means that we should expect total rainfall that is a little below than the normal. Even though it does not indicate any kind of drought, it simply means that the all-India rainfall could remain limited between 95 per cent to 97 per cent of the LPA. It is, however, still not known when the shift towards positive epoch will happen.

How is India’s work for the upcoming Intergovernmental Panel on Climate Change (IPCC) report progressing?

All our efforts for contributing towards this report are going on well and scientists at the Centre for Climate Change Research (CCCR) at the Indian Institute of Tropical Meteorology (IITM), Pune, have developed a model for this purpose. Almost all the required model runs are nearly completed. The IITM has been working on bringing out regional assessments for India and a report is expected to be released some time later this year. The IPCC report, with global-scale features and assessments, will be released during 2021 or 2022. Since no regional-scale analysis is covered in the IPCC report, India is aiming to provide [this]. Our focus remains on furthering our understanding of the effects of heat waves, cold waves, aerosols and tropical cyclones on lives of people in covering South Asia, with special emphasis on India.

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How long will it take before it covers the entire country? Why is annual monsoon rainfall often below average?

What is the next technological leap that India needs for enhancing its forecasting capabilities?

We currently operate a global model on a 12-km grid size — that is, every 12 km, we can get information. This is the highest resolution ensemble system, and at present India has the best model in the world. Consider the ensemble model European Centre for Medium-Range Weather Forecasts (ECMWF), which is otherwise considered the best in the world, that offers a resolution of 16 km. So, Indian models offer higher resolution.

At the regional level, there are weather models operating in a range of 4 km while further narrowing down at city levels. There are weather models operating at 330 metres, which is used at the Indira Gandhi International Airport, New Delhi, mainly for predicting fog. So, if we need to improve forecasting, we will need better resolution for which better computing facilities will be required.

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How long will it take before it covers the entire country? Why is annual monsoon rainfall often below average?

At present, our efforts and discussions are on adopting a technology that can be more energy efficient. This is because, for operating High Performance Computers (HPCs) to run the weather models, we spend several crores of rupees on power bills.

As explained to Anjali Marar