Friday, September 25, 2015

El Niño not solely responsible for poor monsoon

This season, parts of India witnessed one of the driest monsoon spells

India's crucial south-west monsoon season is coming to an end. With less than ten days to go in the official wind up of the season, India is all set to witness another year of below normal rain. All India seasonal rainfall departure will set close to -15 per cent (with slight variance possible). A departure of -15 per cent means rain has been 15 per cent below normal. As per India Meteorological Department (IMD), a departure of -15 per cent comes under a broad "normal" rain category which runs from +19 per cent to -19 per cent. However, things aren't that normal in most of the 16 (out of 36) meteorological subdivisions which till date have recorded "deficient" rain. With a departure of -46 per cent between June 1 and September 20, Eastern Uttar Pradesh tops the list. It is followed by Western Uttar Pradesh at -44 per cent, Punjab at -41 per cent and Haryana at -39 per cent.

This year's monsoon has been dicey and full of ups and downs. Speculations about El Niño affecting India's monsoon were there since early 2015. But the first blow to the chances of a good monsoon came on April 22, when the IMD issued the first part of Long Range Forecast (LRF) of monsoon. This suggested that India would get 93 per cent of normal rain of 89cm (with a variance of plus minus 5 per cent). On June 2, in the second part of LRF, IMD downgraded their previous forecast. The updated forecast suggested that India would get 88 per cent of normal rain in the monsoon period (variance of plus minus 4 per cent). But, to everyone's surprise, the monsoon's mood remained very good during the onset phase (i.e in June). In this month, India received 16 per cent above normal rain. Thirteen subdivisions recorded excess rain, 20 recorded normal rain and only 3 recorded deficient rain. Performance of rain was impressive in Jammu and Kashmir, Rajasthan, Western Madhya Pradesh and other parts of Central India. This was welcoming news for the citizens and it even brought back their hopes of a normal monsoon. Already debt-ridden but encouraged by good rain, farmers in drought-prone areas of Maharashtra like Marathwada took fresh loans and invested heavily in their fields in June hoping for a good harvest. The situation was similar in other parts of India too. No one even imagined what was in the offing.


IMAGE 1- All India rainfall in the month of June '15. Courtesy IMD

Come the fourth week of June, things started changing. Central India witnessed a big dry spell of the monsoon which lasted for around one month. Such dry and wet spells are regular features during the season. Their intensity, frequency and time of occurrence play a very vital role in monsoon's performance, which in turn, influences the agricultural productivity. But, the one month long dry spell which Maharashtra, Gujarat and Madhya Pradesh witnessed was very severe. It severely damaged the kharif crops and even led to their complete destruction at many places in Marathwada and western Maharashtra (Madhya Maharashtra) where irrigated area is too low. It also kicked off drought conditions and agrarian crisis in these areas, leading to acute shortage of drinking water and fodder for thousands of cattle. For the first time in the history of Maharashtra, cattle shelters were set up in the month of August in Marathwada. At the end of July, India's seasonal rain which was 16 per cent above normal in June came down to 5 per cent below normal. The trend continued in August, due to which the amount of seasonal rain further came down to 11 per cent below normal. And on September 20, we are at 14 per cent below normal. This is how June's rain fooled the farmers in suicide-prone areas of Maharashtra. The farmers wouldn't have gone for early sowing had June's rain been scanty and in such a case, the loss certainly would have been lesser than what it is right now.

The overall poor performance of the monsoon confirms the influence of suppressing factors like El Niño. But why was June an exception? Where was El Niño in June? Was it absent?


IMAGE 2- Schematic representation of wet phase of MJO over India. This is reflected by stormy and wet weather over India.   Courtesy: Martin

El Niño was very much present in the month of June! It was trying its best to suppress India's monsoon but it was the Madden-Julian Oscillation (MJO) which gave it a "fight". MJO was discovered by two atmospheric researchers—Roland Madden and Paul Julian in the early 1970s. Simply put, MJO is an atmospheric disturbance which travels around the world in the tropical regions over an average period of 30-60 days. This disturbance propagates eastwards with time and with a varying intensity. The most important property of MJO is that it influences the clouds/rain i.e the process of convection in the areas it travels through. It has two "faces". One face or phase boosts the process of clouds/rain (called the wet phase) while the other one suppresses it (called the dry phase). India's monsoon gets benefitted whenever there are wet phases over the nation. This is because such a phase helps in the rising motion of moist air, which is necessary for cloud formation. The more intense it is, the more rain that particular region gets. In a sense, it counters the negative effects of El Niño for a certain period of time. But when a dry phase enters, it suppresses the rainfall and under the prevailing El Niño conditions, the suppression factor is pretty strong. MJO has dipole nature as can be seen from the above image. Over India, there is a wet phase, but over the Pacific there is dry phase at the same time. This is because the warm moist air that rises over India diverges and cools at upper levels of the atmosphere. This cool and dry air then sinks over the Pacific (see the arrow) causing lack of clouds/rain there.

MJO became active in early June of this year and the Indian subcontinent was blessed by one such wet phase. It continued its presence till the middle of the month which helped the monsoon onset and also gave bountiful rain. But shortly after this, a strong dry phase entered the subcontinent and maintained its presence till mid-July. This dry phase was likely the strongest one seen over India since the last few years. This was the reason why central and other parts of India witnessed such a big dry spell between June-end and July-end. MJO activity has been weak since July due to which the El Niño has maintained its hold over India's monsoon.

El Niño to strengthen further in the coming months


IMAGE 3: Representation of Sea Surface Temperature anomalies in the Pacific Ocean between 31st August and 6th September 2015. Red colour depicts above normal temperatures and blue colour depicts below normal temperatures. Courtesy: NOAA


El Niño is pretty strong now and the Oceanic Nino Index for June-July-August is 1.22°C in the Niño 3.4 region. The Niño 3.4 region (situated at 5°N-5°S, 120°-170°W) is very important as it is that part of the Pacific Ocean whose sea surface temperature anomaly (difference between the observed value and the average value) will reveal if there is an El Niño or not. This means that the average of sea surface temperature between June and August is 1.2°C above normal. This is the third highest value since the year 1950 (we have records from 1950), with the highest being 1.42°C in 1997 (the strongest known El Niño). The latest weekly departure in the Niño 3.4 region is 2.3°C, which suggests a strong departure. The big red patch across the equatorial Pacific Ocean in the above image clearly reflects the strength of El Niño.

El Niño isn't just about warmer sea surface temperatures. The atmospheric circulations too demonstrate changes during it. Weakening or reversal of trade winds is one of the important atmospheric indicators of an El Niño. Gradually, a coupling between the Pacific Ocean and the atmosphere above it is observed and at present we have that! It is because of this coupling that the ocean and the atmosphere are able to influence each other. As per the Bureau of Meteorology, Australia (which independently monitors the Pacific Ocean), these present oceanic and atmospheric indicators are at record levels. El Niño isn't going to end soon! As per the latest advisory from Climate Prediction Centre, there is approximately a 95 per cent chance of it continuing through this winter of the Northern Hemisphere. In fact, these models suggest that El Niño will strengthen around the Northern Hemisphere's winter and it would be a strong one. El Niño's influence will likely be witnessed on India's winter also as it tends to bring warmer than normal winter in India.


IMAGE 4: El Niño's impact during the winter   Courtesy: CPC/NCEP

 Monsoon's withdrawal to resume in north India after some rain

The withdrawal of the south-west monsoon commenced on September 4 from western Rajasthan. After that, the monsoon withdrew from some parts of Punjab and Haryana but the process has been stalled since then. IMD has three criteria for declaring the monsoon's withdrawal. Out of them, two state that rainfall must cease in a particular region for (at least) five days and there must be considerable reduction in the moisture content. However, widespread rainfall is expected in the whole of North India and Rajasthan till Wednesday, September 23 due to the combined effect of a low pressure area and a western disturbance. Jammu and Kashmir will get light to moderate rain in this period due to which there will be a possibility of landslides and some water logging in areas like Srinagar. Rainfall amount will be higher on Tuesday, September 22 in North India. Delhi NCR has been severely hit by dengue. As light rain will continue in Delhi till Wednesday and this will be followed by clearing of weather, there will be a possibility of further increase in dengue cases in the remaining days of September if things aren't handled properly.

The monsoon's withdrawal would stay suspended in this week. But, starting from next week (September 28 onwards), the process of monsoon withdrawal will resume in North India as the rain will cease and humidity will considerably fall.


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