IMD forecasts ‘normal’ rainfall; expert says below-normal rainfall over western, southern, south central and northern parts of India likely
This story has been updated.
This August was officially declared the driest one in the last 123 years. For 2023 to be not declared a drought year climatologically, September needs at least 92 per cent of the month’s average rainfall, Down To Earth (DTE) has calculated.
While the above calculation — 92 per cent — is to avoid being a declared a drought year, for 2023 to experience a ‘normal’ monsoon, September should receive 123 per cent of the month’s average rainfall.
India Meteorological Department has forecast September rainfall to be ‘normal’. However, according to Akshay Deoras, climate scientist at the University of Reading, the United Kingdom, the chances look bleak.
“It doesn’t look like a normal monsoon rainfall ahead. There is an enhanced probability of below-normal rainfall over western, southern, south central and northern parts of India,” he said.
So how alarming is the current situation? To put some context, DTE compared the current situation to other drought years in the last 123 years.
A drought year is when the monsoon seasonal deficiency stands at -10 per cent to the long term average of 1971 to 2020. In the last 123 years, there have been 14 instances or years when the monsoonal deficiency threshold has been over -10 per cent.
Of these 14 drought years, 10 were El Nino years as well. El Nino and La Nina are the warm phase and cool phases of a recurring climate pattern across the tropical Pacific Ocean called the El Nino-Southern Oscillation. La Nina’s three-year run ended in 2023 and El Nino announced its arrival.
Even though analysis of the data suggests no coherent pattern, it would require little over 154 millimetres of rainfall or 92 per cent of the normal rainfall in September for 2023 to avoid being called a drought year.
IMD has forecast favourable Madden-Julian Oscillation (MJO) conditions coupled with positive Indian Ocean Dipole (IOD) development to aid in September reporting normal rainfall.
Like El Nino unfolds in the tropical waters of the Eastern Pacific, IOD is the difference in sea surface temperature stretching from the Arabian Sea to the eastern region of the Indian Ocean along the southern Indonesian coast.
MJO, according to United States’ meteorological agency National Oceanic and Atmospheric Condition, “eastward moving disturbance of clouds, rainfall, winds and pressure that traverses the planet in the tropics and returns to its initial starting point in 30-60 days, on average,” while a positive IOD usually manifests itself in above average rainfall across the Indian subcontinent.
But a normal monsoon is unlikely, according to Deoras. “Only a few areas mainly in eastern India are expected to get above normal rainfall, so the rainfall distribution is likely to be skewed once again,” he said.
The potential benefit from the MJO is going to remain confined to a few days in the month, added Deoras. The Oscillation is likely going to play a role in the development of a monsoon low-pressure system in the first week of September, which is expected to bring rain over eastern and central parts of India.
“The positive IOD normally enhances rainfall along the west coast of India as well as western parts, but the IMD’s long-range forecast is pointing towards below normal rainfall in these regions. So the positive IOD is unlikely to help the monsoon during September 2023,” he further said.
But Deoras expressed caution for 2023 to outwardly be called a drought year.
“Given that there will be some rainfall improvement in early to mid September, we will need to wait until mid September to get a precise estimation of June to September rainfall deficiency,” he said.
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