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Monsoon 2015 could be 93% with ifs and buts

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RG_monsoon_forecast_20150422

The India Meteorological Department has just released it’s long-awaited forecast for the 2015 Indian monsoon. In terms of the quantity of rainfall over the duration of the monsoon season (June to September) the IMD has said it will be 93% of the ‘Long Period Average’. This average is based on the years 1951-2000.

What this means is the ‘national’ average rainfall over the monsoon season for India is considered to be 89 centimetres, or 890 millimetres. So, based on the conditions calculated till today, the ‘national’ average rainfall for the June to September monsoon season is likely to be 830 millimetres.

There are caveats and conditions. The first is that the 93% forecast is to be applied to the long period average for each of the 36 meteorological sub-divisions, and a ‘national average’ does not in fact have much meaning without considerable localisation. The second is that the forecasting methodology itself comes with a plus-minus caution. There is “a model error of ± 5%” is the IMD’s caution.

IMD_categories_201504This first forecast and the model that the forecast percentage has emerged from are thanks to the efforts of the Earth System Science Organization (ESSO), under the Ministry of Earth Sciences (MoES), and the India Meteorological Department (IMD), which is the principal government agency in all matters relating to meteorology. This is what the IMD calls a first-stage forecast.

As with all complex models, this one comes with several considerations. The ESSO, through the Indian Institute of Tropical Meteorology (IITM, which is in Pune), also runs what it calls an ‘Experimental Coupled Dynamical Model Forecasting System’. According to this, the monsoon rainfall during the 2015 monsoon season (June to September) averaged over India “is likely to be 91% ±5% of long period model average”. (The IMD forecast is available here, and in Hindi here.)

This is a lower figure than the 93% headline issued by the IMD. This too should be read with care as there are five “category probability forecasts” that are calculated – deficient, below normal, normal, above normal and excess. Each is accompanied by a forecast probability and a climatological probability (see the table). The maximum forecast probability of 35% is for a below normal monsoon, while the maximum climatological probability is for a normal monsoon.

As before, time will tell and the IMD will issue its second long range forecast in June 2015. Our advice to the Ministry of Earth Sciences and to the IMD is to issue its second long range forecast a month from now, in May, and also to confirm these forecasts two months hence in June, when monsoon 2015 will hopefully be active all over the peninsula. [This is also posted on India Climate Portal.]

Weighing the monsoon winds for El Niño

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Ignoring the torpor of the summer heat, the India Meteorological Department has dusted off the statutory paragraphs that give us in the sub-continent a first indication of what monsoon for the year may be like. The result this year, both scintillating pages, has been made that much more gripping by the inclusion of El Niño. The IMD’s treatment of the normal variables whose interplay determine the nature of any monsoon is perfunctory – which is surprising as the regional and international earth observation networks spare no detail and tend to inundate us with data and analysis.

Clouds and wind, land and farm. The equation that all rural districts make at this time of the year, but which is becoming more difficult with every year that climate change strengthens its grip.

Clouds and wind, land and farm. The equation that all rural districts make at this time of the year, but which is becoming more difficult with every year that climate change strengthens its grip.

But the IMD, especially for the south-west monsoon, has always preferred to be spartan. Perhaps there is some philosophical dictum that us non-meteorologists have yet to grasp, and if so then the only criticism we may be permitted, if the IMD had its way, its to ask for more such teaching. But the IMD does not have its way, and we publics whose monies support its work must continue to demand from the recalcitrant department better, much better, application and communication of its work.

The official release, ‘Long Range Forecast For the 2014 Southwest Monsoon Season Rainfall’, is delivered to us by the IMD, Ministry of Earth Sciences (MoES). There is the usual paragraph claiming a profundity of observation and of the IMD being a standard-bearer of superior method. “Operational models are critically reviewed regularly and further improved through inhouse research activities,” says the IMD. But what we still have, in a tradition that is probably three generations old, is the two stage forecast (one in April, the second in June). [Here is the release in Hindi.]

I think this proves how out of step the IMD – and the Ministry of Earth Sciences (grand title isn’t it?) – is with what citizens of India experience in their villages, towns, fields and hills. For, the south-west monsoon no longer arrives in the first week of June, and it no longer begins to depart by mid-September. Climate change began to alter that comfortable rhythm years ago, but the IMD’s forecasting grindstone is the same, never mind how many new earth observation satellites India pelts into orbit.

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With all these provisos, stated and implicit, what has the IMD told us?

First, that the “experimental ensemble forecast based on IMD seasonal forecast model (SFM) indicates that the rainfall during the 2014 monsoon season (June to September) averaged over the country as a whole is likely to be 88% ± 5% of long period average (LPA)”. This means that in places it could be as low as 83% of the average, and no more than 92% of the average. Combine this with the assessments about the 2014 El Niño and we can see why, far from being satisfied that the IMD is considering both the monsoon and El Niño, we ought to monitor independently both and force the IMD to become more responsive.

Second, that “the experimental forecast based on the coupled dynamical model forecasting system suggest that the monsoon rainfall during the 2014 monsoon season (June to September) averaged over the country as a whole is likely to be 96% ± 5% of long period model average (LPMA)”. This is a more hopeful set, but also shows that the IMD, by telling us of two different scenarios from two models, is hedging its forecast, which is not what its job is.

Third, the IMD has said “the experimental five category probability forecasts for the 2014 monsoon season rainfall over the country as a whole using the experimental dynamical prediction system are 33% (deficient), 20% (below normal), 24% (normal), 6% (above normal) and 17% (excess)”. This means, using this ‘probability’, that a normal monsoon for 2014 has only a 1-in-4 chance whereas a deficient monsoon (that is, total rain less than 90% of the long period average) has a 1-in-3 chance.

This is a prognosis that stands between serious and grim, for a 10% drift towards the lower side of an expected average, for any of our 36 agro-meteorological regions, can spell ruin for farmers and severe hardship for water consumers. How have central and state governments prepared for such a forecast? We have no information, most likely because there has been no preparation (there are contingency plans for the chronically drought-prone districts, but these are normally triggered when there is an official declaration by  the state government that there are conditions of drought in parts of the state). Elections or no elections, El Niño cares not, and it is up to the state governments to make preparations for a monsoon 2014 whose delivery of water already looks uncertain.