IMD predicts normal Monsoon rainfall but says northeast may see less rain

The India Meteorological Department (IMD) Thursday forecast that the monsoons this year are likely to be “normal”. The IMD has said that the southwest monsoon seasonal rainfall, between June and September, will be between 96% to 104% Long Period Average (LPA) – which points to a normal monsoon season, while quantitatively the rainfall is likely to be 99% LPA.

The IMD has, however, indicated that certain areas in the country will receive below normal rainfall during the monsoons, especially states in northeast India that have been experiencing below normal rainfall in the recent years due to climate change. The South West Monsoon rainfall of India contributes 74.9% to the annual rainfall.

While the IMD will release an updated forecast for the monsoons mid-May, detailing rainfall distribution patterns across the country, IMD DG Dr M Mohapatra Thursday said that the dry spells being witnessed over the past few years are part of the “decadal variability in India” of the monsoons.

“The new all-India rainfall normal computed by the IMD now has been based on data from 1971-2020 and is 87 cm, as opposed to the earlier normal of 88 cm computed based on data from 1961-2010,” he added.

“This decadal variability includes large dry as well as wet spells. But the total rainfall received remains the same. Presently, the southwest monsoon is passing through a dry epoch that started in 1971-80. The next decade (2021-30) will come closer to neutral south west monsoon and will enter the wet epoch in the decade after that. So far, temporal variability (in rainfall patterns) has not been detected,” said Dr Mohapatra.

The new rainfall normal has been computed using rainfall data from the 4,132 raingauge stations well distributed over the country representing 703 districts of India.

“During the monsoons, the number of days with heavy rainfall have been increasing, while the number of days with moderate and low rainfall has been decreasing,” he added.

The IMD also said that currently, La Niña conditions are prevailing over the equatorial Pacific region. Climate model forecasts have indicated that La Niña conditions are likely to continue during the monsoon season. At present, neutral IOD conditions are present over the Indian Ocean and the latest forecast indicates that the neutral IOD conditions are likely to continue until the beginning of the southwest monsoon season. Thereafter, enhanced probability for negative IOD conditions is predicted.

As sea surface temperature (SST) conditions over the Pacific and the Indian Oceans are known to have strong influence on the Indian monsoon, IMD is carefully monitoring the evolution of sea surface conditions over these Ocean basins.

Mohapatra pointed out that last year, IMD had implemented a new strategy for issuing monthly and seasonal operational forecasts for the southwest monsoon rainfall over the country by modifying the existing two stage forecasting strategy. The new strategy uses a newly-developed Multi-Model Ensemble (MME) forecasting system based on coupled global climate models (CGCMs) from different global climate prediction and research centres, including IMD’s Monsoon Mission Climate Forecast System (MMCFS), along with the existing statistical forecasting system to generate these forecasts.

The spatial distribution suggests normal to above normal seasonal rainfall is most likely over many areas of northern parts of Peninsular India and adjoining Central India, over foothills of the Himalayas and some parts of Northwest India. Below normal rainfall is likely over many areas of Northeast India, some areas of Northwest India and southern parts of the South Peninsula.

“The below average monsoons in North East India, and certain parts of northwest India and extreme southern peninsula can be attributed to climate change. But the regional impact of climate change on the rainfall patterns needs to be further investigated,” said Mohapatra.

The DG added that the parameters studied by the IMD to assess the impact of the climate change include an analysis of the maximum, minimum and mean daily temperatures, temperatures of oceanic areas and land for the country as a whole, total rainfall in a month and the distribution of rainfall during the monsoon period, as well as frequency of extreme weather events such as cyclones, heatwaves and heavy rainfall events.

The new system was introduced because of demands from different users and government authorities for forecasts of spatial distribution of seasonal rainfall along with the regionally averaged rainfall forecasts for better regional level planning of activities, he said.

Based on the new model, the forecast for the last monsoon had been accurate, said the DG. “Above normal rainfall observed over many parts of plains of northwest India, Central India and Eastern coast were well predicted. Similarly, below normal rainfall observed over the extreme northwest India, northeast India were also as per the forecast. However, the observed below normal rainfall over some parts of central India could not be predicted,” he said.

Leave a Reply

Your email address will not be published. Required fields are marked *

Back to top button