29 May 2014

Pre-monsoon heat approaches 50C in India

Temperatures across India have soared close to 50C in some parts of the country in recent days, ahead of the annual Monsoon.

Whilst such intense heat may sound stifling, it is experienced every year before the heavy rains arrive from the south.

The Indian Monsoon, that takes place between May and September, is a vital source of rainfall across the country, relied upon heavily for agriculture. 


It is caused primarily by the differential heating between the Indian landmass and the oceans to the south of the country, which effectively sets up a huge sea breeze effect.

As summer takes hold in the northern hemisphere, the land over India heats up quickly. This causes hot air to rise upwards from the surface, high into the sky, leading to low pressure forming.

However, at the same time, very moist air feeds in off the oceans from the south or south west, in order to replace the air over the land that has risen up from the surface.

As this moisture-laden air encounters the intense heat and mountains over the land, it rises on a large scale, causing intense rain and thunderstorms that drift northwards across the country over the space of around six weeks.

Where is the monsoon now?

The Indian Meteorological Department tracks the progress of the monsoon in detail, producing daily reports on its position.

The Monsoon arrived in the Andaman sea a few days earlier than normal, however, it has since stalled in the Bay of Bengal and is currently where it should be at this stage of the season.

In the graphic below, the blue line shows the monsoon’s current position, with the red dashed lines indicating where the monsoon would normally be on a given date in a typical year.



2014 monsoon prediction

Each year, the Indian Meteorological Department produces a seasonal forecast on how it expects the monsoon to behave – both in terms of its arrival time and how much rain is likely in comparison to average.

This year, its quantitative forecast expects the monsoon seasonal rainfall to be below normal, at 95 per cent of the long period average, with a model error of plus or minus 5 per cent.

In addition, it also produces a probability-based forecast to highlight the most likely outcome, based on rainfall being deficient, below normal, normal, above normal or excess.

Based on these categories, the following has been predicted;

Deficient: 23 per cent

Below normal: 33 per cent

Normal: 35 per cent

Above normal: 8 per cent

Excess: 1 per cent

All eyes on El Nino

However, this year, there’s an additional factor to take into account when predicting the monsoon: El Nino.

warm_sst_wpEl Nino is a naturally occurring ocean-atmosphere phenomenon that is characterised by unusually warm surface water temperatures in the central and eastern Pacific.

This is of great importance for India because when El Nino occurs, rainfall between May and September tends to be below normal – sometimes to the extent that drought takes hold in north western parts of the country, as well as in Pakistan.

So whilst the monsoon is where it should be at the moment, it will be interesting to see how its progress is affected in the coming months, with El Nino very likely to develop.

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