Climate Change

Monsoon Arrival Delayed, Below-Normal Rainfall Expected: The Weather Channel

By TWC India Edit Team

April 2019

TWC India

File photo of dark monsoon clouds over the city skyline in Mumbai.(SL Shanth Kumar / BCCL, Mumbai)

At a Glance

  • The Weather Company forecasts suggest less than the long-term average rainfall from June to August.
  • The onset of monsoon, which is normally June 1, could be around June 6 this year.
  • The primary factor that may impact the monsoon is persistent El Niño conditions.

Only two months left for the monsoon’s onset! And meteorologists around the world are using various models to try and predict the arrival and extent of rainfall in 2019 in India. Many raw (uncalibrated) climate models suggest a drier June, followed by a wetter July and August—making for an overall normal monsoon.

But wait. Raw models may not give us the complete picture! Working with large amounts of data, raw models are prone to biases and systematic patterns of errors, and may not account for extremes noted in actual weather observations.

In contrast, The Weather Company’s fully-calibrated probabilistic seasonal forecast model, which factors in actual observed weather extremes, indicates that the rainfall from June to August will be less than the long-term average. This means this year’s monsoon will likely be drier in many parts of the country.

Calibrating models using actual observations helps meteorologists improve the accuracy of monsoon and other long-range forecasts. “The process of calibration corrects biases and systematic errors and modifies the forecast distributions to better resolve the extremes that are observed in nature,” explains Dr Todd Crawford, Chief Meteorologist at The Weather Company. Dr. Crawford led the Southwest Monsoon Outlook report that described the above findings.

So what do the signs indicate at present?

The calibrated probabilistic forecast predicts slightly deficit monsoon (June to September) rainfall at around 93% of the long-term average. In addition, the onset of monsoon, which is normally June 1, could be around June 6 this year. Further, the forecast suggests an up to 80% chance of below-normal precipitation in some parts of India.

The Weather Company’s forecast of June-August rainfall in India compared to the long-term average.(Dr Todd Crawford / The Weather Company)

As we move closer to the monsoon, these forecasts will be updated as per global weather patterns. Long-range seasonal forecasts come with inherent uncertainty. The Weather Channel has used currently available evidence, as explained below, to skew its forecast towards later-than-normal onset and lower-than-normal rainfall.

El Niño

The primary factor that may impact the monsoon is persistent El Niño conditions in the Pacific Ocean. Experts have been debating the impact of El Niño on this year’s rainfall for quite a while now. Although there are numerous factors that determine the onset date and amount of rainfall, El Niño often generates the maximum interest, both from meteorologists as well as the general public, as it is considered one of the biggest and most important determining factors.

“While there are two months for the monsoon to arrive in the mainland of India, its formation is already underway. In fact, in a few weeks from now, we should start seeing the monsoon winds shaping up in the southern Indian Ocean. Most of the conditions related to the current El Niño have pretty much maintained themselves since February end. While there is no consensus regarding when the current El Niño will reach its peak intensity, its presence during the early part of the monsoon season is becoming increasing likely. Thus, authorities in India (esp. in the drought hit regions) should start thinking about the potential situation”, says Akshay Deoras, a meteorologist and researcher at the University of Reading, UK.

In normal (neutral El Niño-Southern Oscillation or ENSO) conditions, the easterly trade winds pool warm water in the western Pacific Ocean region near Australia and Indonesia. During El Niño (positive ENSO conditions), the trade winds weaken or reverse causing the area of warmer water to spread across central and eastern Pacific towards South America.

The monsoon arrives to India due to the difference in heat between the land and ocean. The differential heat leads to a pressure difference which is such that land (Indian subcontinent) has relatively lower air pressure than the ocean. Since winds always flow from high pressure to low pressure, the the monsoon winds blow towards India. El Niño induces changes in these wind patterns and weaken south-westerly monsoon flow. Thus, El Niño and the associated atmospheric circulation is often associated with lower-than-normal rainfall for the country.

File photo of a farmer looking at the monsoon clouds near Jaipur.(Bhagirath Basnet / BCCL, Jaipur)

While the formation of a weak El Niño was confirmed by Met departments like NOAA in January, the India Meteorological Department (IMD) confirmed it only this month. Historical data suggests that more often than not, monsoons following El Niño winters arrive later than normal in India. Research indicates a weak relationship between the later onset of monsoon and lower-than-normal rainfall.

In addition, the latest forecasts suggest a 70% probability that El Niño conditions will prevail during the early monsoon season. The Indian Ocean Dipole, a counterpart of El Niño in the Indian ocean, is neutral at present, and may not have any significant impact on the monsoon rainfall this year.

Multi-decadal dry phase

Analysing monsoon data from the past 150 years, one observes an approximately 30-year cycle comprising alternate phases of high and low rainfall. This multi-decadal variability in monsoon rainfall is primarily dependent on variability in ocean temperatures. Currently, we are in a drier multi-decadal phase, and Dr Crawford suggests that in case of limited information, one should always skew an early season prediction towards the dry side.

File photo of Bailey road in Patna during monsoon rain.(K M Sharma / BCCL, Patna)

The monsoon, which highly influences the growth of India’s $2.9 trillion economy, accounts for up to 70-80% of rainfall in the country. It feeds the agricultural economy— a lifeline to over 70 crore people across the country. Early forecasts help policymakers and authorities plan well in advance.

Even though a good monsoon is important across India, this year, it is absolutely crucial for a few regions. Gujarat, Marathwada, north Karnataka, Vidarbha, Madhya Maharashtra, Rayalaseema, West Rajasthan, and the entire east and northeast parts of India have faced significant deficits in rainfall last year. Another deficit this year may spell trouble for water security, agriculture, and livelihood in these regions.

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