Normal Indian monsoon forecast offers relief

The India Meteorological Department (IMD) has forecast normal rainfall during the monsoon months of June-September 2021.

As reported by the Weather Channel, the upcoming southwest monsoon season may restore some form of normalcy to the year. The report states that termed as the ‘Real Finance Minister of India’ by former President Pranab Mukherjee, the monsoon season is crucial for the Indian economy. Its immense influence on the farming sector also impacts the overall livelihood of more than half of India’s population, and therefore, bountiful monsoon showers are absolutely essential for the country as a whole.

Now, in its first long-range forecast for the 2021 southwest monsoon season, the IMD has predicted that the seasonal rainfall across India is likely to be 98% of the Long Period Average (LPA), with a model error of ±5%.The LPA refers to the average monsoon rainfall from 1961-2010, which stands at 88 cm (880.6 mm to be precise). Accordingly, this forecast of 98% indicates that a total of around 86.2 cm rainfall is expected across the country during the entirety of this year’s monsoon season. It has added that there is also a 21% chance of excess rainfall this season. The IMD declares a monsoon season ‘normal’ when rainfall is between 96% and 104% of the LPA. The last two years, India recorded excess rainfall of 110% and 109% of LPA during the monsoon season.

The predictions are also based on the global model forecast, the latest of which indicates that the neutral El Nino-Southern Oscillation (ENSO) conditions that currently prevail over the Pacific Ocean are likely to continue over the equatorial Pacific during the course of the monsoon season.

However, the IMD also adds that the neutral Indian Ocean Dipole (IOD) conditions that currently exist over the Indian Ocean are expected to change, with negative IOD conditions likely to develop during the ensuing monsoon months. This weather condition is usually results in warming and more rainfall in the eastern Indian Ocean and cooling and less rainfall in the western Indian Ocean.

Global climatic factors such as the ENSO will not be at play during the monsoon season of 2021 as its cooling phase, La Nina, which began in October 2020 has come to an end.  There is also very little chance of the development of the warming El Nino. Since 1951, only three of the total 14 years that followed a La Nina year had deficient rainfall. Two of them were El Nino years which are generally linked to below-normal or deficient monsoon seasons.

The department, for the first time, will be predicting how India’s rainfall will be distributed across its various regions. The spatial seasonal forecasts with regional averages are in keeping with the demands from users and government authorities for better local planning.

For instance, in its initial spatial distribution forecast, the IMD predicted that the rainfall over many parts of northern, eastern and north eastern India might receive below-normal rainfall, while most parts of western, central and southern India might receive normal or above-normal rainfall.

Further, as the Weather Channel highlights, as per the state-wise rainfall probability forecast, the likes of Himachal Pradesh, Uttarakhand, Punjab, Rajasthan, Madhya Pradesh, Maharashtra, Telangana, Karnataka, Kerala and Arunachal Pradesh are all likely to receive above-average rainfall in most places. But on the flip side, a majority of the places located in Jammu & Kashmir, Ladakh, Haryana, Delhi, Bihar, Jharkhand and Meghalaya may be in for below-average precipitation during the monsoon season. These forecasts are prepared using the state-of-the-art Statistical Ensemble Forecasting System (SEFS) that was developed indigenously by the IMD.

As the sea surface temperatures over the two oceans have a strong influence on the Indian monsoon, the IMD will continue to carefully monitor the evolution of the sea surface conditions over these ocean basins, as even minor changes can lead to wide gaps between the forecasted figures and actual figures. Such an instance was witnessed last year itself, when the early seasonal outlook predicted the 2020 monsoon rainfall to be 100% of its LPA, whereas the actual rainfall received over the country was 109% of its LPA – the third-highest since record-keeping began.

Following this first stage forecast in April, the IMD will also release the second stage of its seasonal monsoon outlook by the end of May 2021. It will consist of additional countrywide monthly rainfall forecasts for July, along with forecasts for seasonal rainfall (June to September) for the four homogeneous regions of India.