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Why IMD’s rain math doesn’t add up

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Each blue bar represents the actual rainfall recorded by a district as a percentage of its normal. There are 614 district recordings in this chart.. The red dotted line is the 100% mark, and many of the bars end below, or way below, this mark. This is the district-level view of cumulative rainfall over eight rain weeks using the IMD's own data.

Each blue bar represents the actual rainfall recorded by a district as a percentage of its normal. There are 614 district recordings in this chart.. The red dotted line is the 100% mark, and many of the bars end below, or way below, this mark. This is the district-level view of cumulative rainfall over eight rain weeks using the IMD’s own data.

Over eight weeks of recorded monsoon rain, the district-level data available with the India Meteorological Department (IMD) portrays a picture that is very different from its ‘national’ and ‘regional’ advice about the strength and consistency of rainfall.

In its first weekly briefing on the monsoon of August 2014, IMD said: “For the country as a whole, cumulative rainfall during this year’s monsoon (01 June to 30 July 2014) has so far upto 30 July been 23% below the Long Period Average.” Out of 36 meteorological sub-divisions, said the IMD, the rainfall has been normal over 15 and deficient over 21 sub-divisions.

The four regional readings that make IMD's data look less worrisome than it actually is.

The four regional readings that make IMD’s data look less worrisome than it actually is.

However, here is a far more realistic reading of the monsoon season so far, from the IMD’s own data. For the 614 individual readings from districts that have regular rainfall readings, we have the following: 86 districts have registered scanty rainfall (-99% to -60%); 281 districts have registered deficient rainfall (-59% to -20%); 200 districts have registered normal rainfall (-19% to +19%); and 47 districts have registered excess rainfall (+20% and more).

What this means, and the chart I have provided to illustrate the 614 individual values leaves us in no doubt, is that 367 out of 614 districts have had meagre rain for eight weeks. This also means that over eight weeks where there should have been rainfall that – as the IMD predicted in early June – would be around 95% of the ‘long period average’, instead three out of five districts have had less than 80% of their usual quota.

Monsoon 2014 and a third dry week

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05 to 11 June is the first week. 12 to 18 June is the second week. 19 to 25 June is the third week. The bars represent the weeks and are divided by IMD's rainfall categories, with the length of each category in a bar showing the proportion of that category's number of districts. The colours used here match those used in IMD's weekly rainfall map (below) which displays the category-wise rainfall in the 36 meteorological sub-divisions (but not by district).

05 to 11 June is the first week. 12 to 18 June is the second week. 19 to 25 June is the third week. The bars represent the weeks and are divided by IMD’s rainfall categories, with the length of each category in a bar showing the proportion of that category’s number of districts. The colours used here match those used in IMD’s weekly rainfall map (below) which displays the category-wise rainfall in the 36 meteorological sub-divisions (but not by district).

IMD's weekly rainfall chart, 19 to 25 June

IMD’s weekly rainfall chart, 19 to 25 June

We now have rain data for three complete weeks from the India Meteorological Department (IMD) and for all the districts that have reported the progress of the monsoon.

The overall picture remains grim. In the third week of the monsoon the number of districts that reported normal rains in that week (-19% to +19% of the average) is only 74. No rain (-100%) was reported by 71 districts Scanty rain (-99% to -60%) was reported by 221 districts, deficient rain (-59% to -20%) was reported by 125 districts, excess rain (+20% and more) was reported by 129 districts, and there was no data from 21 districts.

IMD_districts_table_3_weeksThe Department of Agriculture and Cooperation, of the Ministry of Agriculture, has already issued its guidance to states on the contingency plans to be followed for a delayed monsoon. That is why it is important to make available the district-level normals and rainfall departures – the meteorological sub-divisions are too broad for such analysis and are irrelevant to any contingency plans and remedial work.

By end-June, when the IMD updates its outlook for the rest of monsoon 2014, we expect more detailed assessments of the districts to be publicly available – the agromet (agricultural meteorology section) already provides this to the states, with state agriculture departments given the responsibility of ensuring that the advice – which is especially important for farmers to plan the sowing of crop staples – reaches every panchayat.

Written by makanaka

June 28, 2014 at 09:09

The new measure of monsoon

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Districts reporting monsoon data, over two weeks, colour-coded under a revised categorisation (explained in the text) for weekly rainfall. The left bar in each pair is the second week, the right bar is the first. Most districts are coloured light red, signifying rainfall much below the weekly normal. Peach is for the lesser deficient category. Green is normal. The two blue hues - lighter and darker - are for the two excess categories. It is immediately apparent that 485 out of 618 reporting districts (78%) have experienced less rainfall than they should have at this stage of the monsoon.

Districts reporting monsoon data, over two weeks, colour-coded under a revised categorisation (explained in the text) for weekly rainfall. The left bar in each pair is the second week, the right bar is the first. Most districts are coloured light red, signifying rainfall much below the weekly normal. Peach is for the lesser deficient category. Green is normal. The two blue hues – lighter and darker – are for the two excess categories. It is immediately apparent that 485 out of 618 reporting districts (78%) have experienced less rainfall than they should have at this stage of the monsoon.

The changes that we find in the patterns, trends, intensity and quantity of India’s monsoon now require an overhaul in the way we assess what is satisfactory or not for environmental and human needs. India’s summer monsoon is already late, and where it is late but active it is weak. The indications from the central earth science agencies (including the India Meteorological Department), from the Indian Institute of Tropical Meteorology, from the National Centre for Medium Range Weather Forecasting are that it will be the end of June before the summer monsoon system settles over central India and the western Gangetic plains. Even so, it will be a relief from the searing temperatures but will not assure sowing conditions for farmers and cultivators, nor will it add to the stores of water in major and minor reservoirs.

In this commentary written for India Climate Portal, I have explained why IMD’s hoary top level categorisation of rainfall weekly quantities in the subdivisions must be replaced, both for what they describe and for how frequently they are described. These currently are: ‘normal’ in a subdivision is rainfall that is up to +19% above a given period’s average and down to -19% from that same average; likewise excess is +20% and more, deficient is -20% to -59% and scanty is -60% to -99%. The ‘normals’ are calculated based on the mean weekly rainfall for the period 1951-2000 with monitoring done in 641 districts distributed amongst the 36 meteorological subdivisions.

By categorising rainfall ‘normals’ and departures from  ‘normal’ to become more administratively impelling – these proposed corrections also simplify the interpretations possible for rainfall above and below ‘normals’ – greater awareness and preparedness of administrations, key agencies and citizens to the deficiencies of monsoon can be fostered. For the district tables below therefore, I have re-cast the categories as follows (all based on the long-term average provided by IMD): Normal in a district is +5% to -5%; Deficient 1 is -6% to -20%; Deficient 2 is -21% and more; Excess 1 is +6% to +20%; Excess 2 is +21% and more.

Whereas, for the same second rainfall week the IMD categories were ‘No Rain’ in 80 districts, ‘Scanty’ in 241 districts and ‘Deficient’ in 130 districts, under the proposed revision they will simply be ‘Deficient 2’ with 449 districts – thereby showing dramatically how widespread the conditions of the late and weak monsoon 2014 are – and ‘Deficient 1’ with 36 districts. Please read the rest at 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.

IMD_monsoon_2014_probability

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.