The India Climate Observatory

Commentary, action and research on climate and development in India

India looks to a normal monsoon 2020

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The states with coastlines along the Bay of Bengal have been anxiously watching the unfolding of the giant movements of wind, sea moisture and pressure which is now called Cyclone Amphan.

Once that cyclonic threat has played itself out – and until it does Odisha, West Bengal and Assam will be on high alert – the countdown to normal rains will resume.

On 15 April, the India Meteorological Department (IMD) issued its customary first phase long range forecast for the south-west monsoon. And the primary take-away was: “South-west monsoon seasonal (June to September) rainfall over the country as a whole is likely to be normal (96-104%).”

Quantitatively, said the IMD, the monsoon seasonal (June to September) rainfall is likely to be 100% of the Long Period Average (LPA) with a model error of ± 5%. The LPA of the season rainfall over the country as a whole for the period 1961-2010 is 88cm.

IMD’s forecast based on the Monsoon Mission Coupled Forecasting System (MMCFS) uses atmospheric and oceanic initial conditions during March 2020. The forecast was computed as the average of 51 ensemble members. The forecast based on the MMCFS suggests that there is a high probability (70%) for 2020 monsoon rainfall to be above normal to excess (more than 104% of LPA).


The Indiaclimate Rainfall Index 2019

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We have compiled the Indiaclimate District Rainfall Adequacy Index for the monsoon season of 2019. As with our previous editions of the index series, this one for the 2019 monsoon applies our innovation to the communicating of the weekly changes in rainfall adequacy as recorded by the India Meteorological Department (IMD).

The graph (or visualisation as any such illustration is called nowadays, a word that makes the simple graph or chart sound sophisticated, but which usually complicates matters instead of simplifying them) is easy enough to read and interpret. What you have is several vertical bars, each corresponding to dates a week apart. The bars are made up of coloured segments – there are 11 coloured segments and one grey segment, a total of 12 segments.

Each of the 11 colours represents the number of districts whose rainfall readings for a week (the week till the date given) fall within the parameters given in the accompanying legend. There are three groups of colours: three segments in the ‘normal’ ranges, four segments in the ‘excess’ ranges and four segments in the ‘deficient’ ranges. Grey represents no data for that week.

The gradation of the segments is based on, but is not a copy of, the grades used by the UN Food and Agriculture Organisation’s (FAO) Global Information and Early Warning System (GIEWS) indicators for precipitation. The numbers that we use are from the IMD’s Hydrometeorology Division, which releases its ‘rainfall departures’ table every week. We take these numbers, reprocess them and redistribute them across the 11 grades.

It is a much more readily readable graph and provides for quick interpretation. The grades are finer than the six used by the IMD: normal (+19% to -195), excess (+20% to +59%), large excess (+60% or more), deficient (-20% to -59%), large deficient (-60% to -99%), no rain (-100%).

Our index, in which most segments are of 20 percentage points, is designed for local administrations – in districts but also municipal bodies – to take their cues from weekly signals and prepare if need be for a drought-like situation with water shortages or a flood-like situation with inundation.

How does it work in practice? Let’s look at the district of Guna, in Madhya Pradesh, in the meteorological sub-division of Western MP. The first two monsoon weeks, ending 5 June and 12 June, Guna received no rain (that is, -100% of the rainfall it normally receives in those weeks) and that corresponds to the D4 indicator. The next week, ending 19 June, it received -29% which is D1, the fourth week (26 June) it slipped back to -72% which is D3, the following week (3 July) it improved to -32% which is again D1 and in the sixth week (10 July) Guna received +34% which took it into the E1 grade.

Normally, a district that has received no rainfall or neglible rainfall for six weeks becomes a candidate for a drought-like condition – water sources after the long and hot summer have dried up and crops become parched. If such conditions continue for another two weeks, the state administration must roll out relief measures.

In our example, for the five weeks until the week of 3 July Guna had two D4s, one D3 and two D1s before coming out of the D grades. Our index gives the district (or town) administration the means with which to set their own triggers for action. If the water sources in the district were still at 10%-15% of their water holding capacities by the week of 3 July, then they could consult the medium term forecasts to gauge whether likely rainfall will be enough to hold off relief action. If not, and stored water slipped under 10% with uncertain forecasts, they could ask for relief and issue appropriate crop advisories.

Our index graph – the stacked and segmented bar chart I am sorely tempted to call a ‘signature’ – is a representation of the numbers in the rainweeks table we compile. This table has 684 components which are the districts, each of which has a rainfall reading for the week given (in millimetres) and a rainfall departure (in %). The graph is a set of stacked bars for each week, with each segment sized according to the number of districts in the grade that the segment corresponds to.

What does the index graph for six weeks tell us? The first two monsoon weeks were alarming, with 342 and then 356 districts in the D4 grade. The situation has slowly improved thereafter, with the latest week, that of 10 July, being the best so far – it has 80 districts in the N1 grade. That last week also has for the first time in monsoon 2019 more E grade districts than D grade districts. What needs to be looked out for is districts that have been in the D4 and D3 grades for four and more weeks and whose recovery is patchy. That monitoring becomes much easier with the Indiaclimate District Rainfall Adequacy Index.

Rahul Goswami

Late, but on the way

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At this point, the monsoon 2019 system is farther away, in terms of its movement, than where it is normally found at this time of the year. The India Meteorological Department maintains its maps showing the movement of the system through late May and early June.

Judged against its averaged movement over the last decade and over a 50-year long-term average, the northern limit of the system is some 450 kilometres away from where it usually is in the south-west Bay of Bengal, and is about 400 kilometres away from the more easterly end of the same perimeter in the east-central Bay of Bengal. Whereas around 27 May the monsoon system would have normally been some 150 kilometres north of the Andaman Islands, now it is at 11N (near Little Andaman).

This delay has no bearing on the forecast for the overall adequacy of rainfall during monsoon 2019 because, as the IMD has said, the large-scale features which influence our monsoon are favourable, these being:
* Weak El Niño conditions that are prevailing over the equatorial Pacific Ocean; the latest Monsoon Mission Climate Forecasting System (MMCFS) forecast indicates that these conditions are likely to continue during the monsoon season but with reduced intensity.
* Neutral Indian Ocean Dipole (IOD) conditions over the Indian Ocean; the latest MMCFS forecast indicates these conditions are likely to continue during the monsoon season.

The weekly outlooks are as follows.
The week 24 May to 30 May: the south-west monsoon cloud cover belt moves into sea regions – the south-east Arabian Sea, the south-west and south-east Bay of Bengal, and the north Andaman Sea. Showers in the entire north-eastern region with heavier daily rain (5-10 mm/day) in Manipur, Nagaland and Assam hills. Light showers in Karnataka, Kerala, adjacent Tamil Nadu and Rayalaseema.

The week 31 May to 06 Jun: the south-west monsoon cloud cover belt does not advance further into the Arabian Sea while it moves further north into the east-central Bay of Bengal. The north-east region continues to have showers as the eastern Himalayan region is fully covered. Lower Assam and Meghalaya to have heavier showers of up to 20 mm/day. The spread of light showers in Tamil Nadu is wider as the north Lankan gap between the cloud fronts over the Arabian Sea and Bay of Bengal closes, light showers (up to 5 mm/day) continue in Kerala and south interior Karnataka.

The week 07 Jun to 13 Jun: the main feature is the advance of the south-west monsoon cloud cover belt into the east-central Arabian Sea (off the central Konkan coast). With the limits of the south-west monsoon cloud cover belt remaining as they were over the Bay of Bengal, light showers extend over Tamil Nadu, south interior and coastal Karnataka, Goa and the Maharashtra Konkan with heavier showers (5-10 mm/day in Kerala). All states of the north-east continues to receive heavier showers (10-20 mm/day) and the western Himalaya – all divisions of Jammu & Kashmir, the northern halves of Himachal Pradesh and Uttarakhand – receive light showers.

The week 14 Jun to 20 Jun: consolidation of the south-west monsoon cloud cover belt over the seas with the east-central and north-east Arabian Sea fully reached, the north-east Bay of Bengal likewise, and its north-west entered. This brings heavier daily rain (up to 20 mm/day to all states of the north-east and light showers to West Bengal, parts of Bihar, Jharkhand, parts of Odisha. The entire west coast has rain with the northern precipitation line from Thane (20N) to Latur (18N), to Warangal (18N) and Kondagaon (in Chhattisgarh, 20N), to Rayagada (in Odisha, 19N). Light showers also in the western Himalayan region (up to 5 mm/day).

Misreading monsoon

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As usual in May, there is a welter of forecasts and opinions about the monsoon, the great majority of which are short on understanding and shorter on elementary science. The media – newspapers, television news channels, their websites – are to blame for spreading half-baked forecasts and wild prognoses. Not one of the numerous newspapers and TV channels, whatever the language they employ, bother to provide their reporters a basic grounding in the climatological system that gives us our monsoon.

In the first place, the India Meteorological Department (IMD) issues an operational forecast for the south-west monsoon season (June to September) rainfall for the country as a whole in two stages. The first stage forecast is issued in April and the second stage forecast is issued in June. These forecasts are prepared using state-of-the-art Statistical Ensemble Forecasting system (SEFS) and using the dynamical coupled Ocean-Atmosphere global Climate Forecasting System (CFS) model developed under Monsoon Mission of the Ministry of Earth Sciences.

On 15 April 2019 the IMD issued its first stage forecast. Based on our own in-field observations from the west coast, from the patterns of maximum termperature bands and variations in the lower and central peninsular region, from the sea surface temperatures in the Arabian Sea particular its southerly reaches and ditto for the Bay of Bengal, and from the wind patterns that can be experienced at various places in the peninsula and on the west coast, we find the IMD first stage forecast to be reliable.

It is the chronically ignorant media – which over the last few years has displayed a tendency to prefer some so-called private sector weather forecasters instead of what the Ministry of Earth Sciences provides – found irresponsibly claiming that the monsoon of 2019 will be ‘deficient’ and will also begin ‘late’. Neither of these terms is sensible in any way, and we take no satisfaction in noting that only a media that is insensible to planetary and mesoscale events like climate, will employ such insensible terms in reporting that is meant to educate and benefit the public.

IMD’s April forecast used the following five predictors: 1. the Sea Surface Temperature (SST) Gradient between North Atlantic and North Pacific (in December and January), 2. the Equatorial South Indian Ocean SST (in February), 3. the East Asia Mean Sea Level Pressure (in February and March), 4. North-west Europe Land Surface Air Temperature (in January), and 5. Equatorial Pacific Warm Water Volume (in February and March).

There are two forecasts the IMD makes. One is based on the Monsoon Mission CFS Model, which considers global atmospheric and oceanic initial conditions up to March 2019 and use 47 ensemble members (or kinds of data). The forecast based on the CFS model suggests that the monsoon rainfall during the 2019 monsoon season (June to September) averaged over the country as a whole is likely to be 94% ± 5% of the Long Period Average (LPA).

The second is the forecast based on the operational Statistical Ensemble Forecasting system (SEFS). This shows that quantitatively, the monsoon seasonal rainfall is likely to be 96% of the Long Period Average (LPA) with a model error of ± 5%. The SEFS comprises five category probability forecasts for the June to September rainfall over the country as a whole:

Overall therefore the IMD forecast is for the 2019 monsoon rainfall to be near normal. The IMD has already pointed out (which can be seen from the probabilities of the categories given in the table) that there is only a small chance for the monsoon rainfall to be above normal or excess. In view of the weather events and the climatological changes that we are seeing from day to day in May, ascribing a ‘lateness’ to the monsoon is absurd. Monsoon conditions already exist in and over the Indian land mass and in and over the great watery zones extending southwards from latitude 8 degrees North – and that is why we will find rain-bearing clouds crossing the south-western coastline in the first week of June 2019.

Rahul Goswami

‘Fani’ aims for Odisha, AP

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Update: Cyclone Fani will make landfall on the coast on 3 May. Depending on whether the Extremely Severe Cyclonic Storm (IMD’s classification) gains more speed over the Bay of Bengal, Fani could cross the coast as early as 1000 hours on 3 May.

Based on the weather charts released by IMD and corroborated by the climatological forecasts produced by the World Meteorological Organisation’s members, Fani will cross the coast between Kakinada, East Godavari district, Andhra Pradesh, and Puri, district Puri, Odisha, which is about 60 km south of Bhubaneshwar.

Previously: The India Meteorological Department has issued a forcast for and warning about a cyclonic storm which as of today (27 Apri) is a low pressure area lying over the East Equatorial Indian Ocean and adjoining south-east Bay of Bengal.

It is already intensifying into a depression over the East Equatorial Indian Ocean and adjoining central parts of the southern Bay of Bengal and will further intensify into a cyclonic storm. Thereafter the storm is forecast to move north-westwards along and off the east coast of Sri Lanka near the north Tamil Nadu coast on 30 April.

The IMD has already issued warning to fishermen about strong winds. Wind speed reaching 45-55 kmph gusting to 65 kmph over East Equatorial Indian Ocean and adjoining central parts of the southern Bay of Bengal are already being recorded. Gale wind speeds will be reached of 65-75 kmph gusting to 85 kmph over the south-west Bay of Bengal and adjoining Equatorial Indian Ocean by 27 April.

Thereafter 80-90 kmph gusting to 100 kmph over the south-west Bay of Bengal and adjoining Equatorial Indian Ocean and along and off the Sri Lankan coast on 28 April and 90-100 kmph gusting to 115 kmph over the south-west Bay of Bengal, along and off the Sri Lankan coast and off the Tamil Nadu and Puducherry coast on 29 April. The sea condition will be very rough in all these areas.

There will be light to moderate rainfall at many places with heavy rainfalls at isolated places in north coastal Tamil Nadu on 30 April and 1 May and over Kerala on 29 and 30 April. Light to moderate rainfall at many places with heavy rainfall at isolated places is also very likely over south coastal Andhra  Pradesh on these dates.

Forecast updates are available here.

A mixed report for the monsoon so far

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The India Meteorological Department in its ‘Long Range Forecast for the Rainfall during Second Half (August –September) of the Southwest Monsoon 2018’ has said:
(a) The rainfall during August 2018 is likely to be 96 ± 9% of LPA and expected to be higher than was predicted in June.
(b) Quantitatively, the rainfall for the country as a whole during the second half of the season (August and September) is likely to be 95% of LPA with a model error of ±8%.
(c) The tercile probability forecasts for the rainfall over the country as a whole during the 2018 second half of the monsoon season are: 47% forecast probability that it will be less than 94% of the LPA (below normal), 41% forecast probability that it will be between 94% and 106% of the LPA (normal), and only 12% forecast probability that it will be over 106% of the LPA (above normal).
The Department said that “distribution of rainfall is very good over all parts of the country except Bihar, Jharkhand and NE States. Such a scenario of favourable distribution of rainfall is expected to continue during rest of monsoon season of 2018 so as to remain favourable for agricultural operations”.

The IMD in its latest weekly ‘performance sheet’ on rainfall has calculated the cumulative rainfall up to 1 August 2018 on an ‘area weighted’ basis as being 431 mm as compared with a normal of 462 mm. But this is a measure that doesn’t tell us anything local and we have advised the IMD to abandon it. What is more useful is the enumerating of subdivisions according to cumulatie rainfall: by 1 August, there were 28 which had normal rainfall, 7 which had deficient, and one which had excess. For this period – monsoon rainfall until 1 August – this year has had the most number of subdivisions with normal rainfall in the last five years.

However it is a concern that five of the seven subdivisions which up to 1 August 2018 have had deficient rainfall are in the East and North-East India region and they are: Arunachal Pradesh (-36%), Assam and Meghalaya (-33%), NMMT which is Nagaland Manipur Mizoram Tripura (-25%), Jharkhand (-24%) and Bihar (-22%). The other two subdivisions with deficits are Rayalaseema (-41%) and Lakshadweep (-43%).

In states, Uttar Pradesh has the largest number of districts (26) registering deficient rainfall up to 1 August 2018, even though 25 of the state’s districts have had normal rainfall for the period and 18 have had excess or large excess. Bihar has 24 districts which have registered deficient rainfall for this period, followed by Jharkhand (15), Assam (14), and Gujarat, Tamil Nadu and Karnataka each with 13.

Three views of monsoon 2018

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The India Meteorological Department (IMD) on 16 April had issued its first long range forecast for the 2018 South-West Monsoon season, which the IMD has historically taken to be 1 June to 30 September. The IMD had said that the “monsoon seasonal rainfall is likely to be 97% of the Long Period Average with a model error of ± 5%”. The IMD had also said that its forecast “suggests maximum probability for normal monsoon rainfall (96%-104% of the long period average) and low probability for deficient rainfall during the season”.

In early June, the IMD will issue its second long range forecast for the 2018 monsoon. Until then, we have studied three of the more reliable (in our view) international multi-model ensemble forecasts for the monsoon. What are ensemble forecasts? Each consists of several separate forecasts (some ensembles use 50) forecasts made by the same computer model – these are run on super-computers such as the High Performance Computer System of the Ministry of Earth Sciences (one is at the Indian Institute of Tropical Meteorology in Pune with 4.0 petaflops capacity and the other at the National Centre for Medium Range Weather Forecasting in Noida with 2.8 petaflops capacity).

The MME forecast is based on estimated precipitation anomalies relative to the period 1993-2016, based on initial conditions calculated at the beginning of May 2018. Four blocks of three months each.

The separate forecasts that make up one ensemble are all activated from the same starting time. The starting conditions for each differ from each other to account as far as possible for the staggering number of climatological, atmospheric, terrestrial and oceanographic variables that affect and influence our monsoon. The differences between these ensemble members tend to grow as the forecast travels two, three, four and more months ahead of the present.

We have considered the ensemble forecasts for the 2018 monsoon of the Multi-Model Ensemble (MME) of the USA National Centers for Environmental Prediction, the NOAA Climate Prediction Center and the European Centre for Medium-Range Weather Forecast (ECMWF). In this order, we find that the MME is optimistic, the NOAA CPC is largely neutral and the ECMWF forecast is somewhat pessimistic. The forecasting periods are in blocks of three months.

Here are the details:

(1) The MME forecast, precipitation anomalies relative to the period 1993-2016, based on initial conditions calculated at the beginning of May 2018.
June July August (JJA) – west coast and Konkan, coastal Andhra Pradesh and Odisha, West Bengal, part of the North-East, the entire upper, middle and lower Gangetic region (Uttarakhand, Himachal, Uttar Pradesh, Bihar, Jharkhand), Madhya Pradesh, Chhattisgarh, Maharashtra and Telengana to have up to +1 mm/day. Rest of India other than Gujarat (-0.5 mm/day) normal.
July August September (JAS) – Gujarat to have up to -1 mm/day, Rajasthan up to -0.5 mm/day, Sikkim, Brahmaputra valley and Arunachal Pradesh up to -0.5 mm/day. Himachal Pradesh and Uttarakhand up to +0.5 mm/day, Madhya Pradesh, Odisha, Chhattisgarh, Jharkhand and West Bengal up to +0.5 mm/day. Andhra Pradesh and Tamil Nadu up to -0.5 mm/day.
August September October (ASO) – Gujarat up to -0.5 mm/day. Tamil Nadu up to -1 mm/day. Kerala and adjacent Karnataka up to -0.5 mm/day. Madhya Pradesh, Chhattisgarh, Odisha, West Bengal up to +1 mm/day. Tripura, Mizoram, Manipur, Nagaland, Uttarakhand, Himachal Pradesh up to +0.5 mm/day
September October November (SON) – Tamil Nadu, Kerala and adjacent Karnata up to -1 mm/day. Maharashtra, Madhya Pradesh, Chhattisgarh, Odisha, West Bengal, Himachal Pradesh and Uttarakhand up to +0.5 mm/day.

The NOAA CPC forecast is based on estimated seasonal precipitation anomalies using initial conditions of 30 April 2018 to 9 May 2018. Three blocks of three months each.

(2) The NOAA CPC forecast, seasonal precipitation anomalies using initial conditions of 30 April 2018 to 9 May 2018.
May June July (MJJ) – for most of India a normal reading (+0.5 to -0.5 mm/day fluctuation) and for the west coastal, Konkan, Kerala, south Tamil Nadu and coastal Andhra Pradesh areas variation of up to +1.5 mm/day.
June July August (JJA) – for most of India a normal reading (+0.5 to -0.5 mm/day fluctuation).
July August September (JAS) – normal for most of India. Some areas in the central Deccan plateau, on the west coast and east coast variation of up to -1 mm/day.

The ECMWF forecast is based on estimated mean precipitation anomaly based on climate period data of 1993-2016 and initial conditions as on 1 May 2018. Four blocks of three months each.

(3) The ECMWF forecast, mean precipitation anomaly based on climate period data of 1993-2016 and initial conditions as on 1 May 2018.
June July August (JJA) – all of the southern peninsula and part of the Deccan region (Kerala, Tamil Nadu, Karnataka, Andhra Pradesh, part of Telengana up to -100 mm for the period. West Bengal, Bihar, Jharkhand, Uttar Pradesh up to +100 mm for the period.
July August September (JAS) – all of the southern peninsula and the Deccan region – Kerala, Tamil Nadu, Karnataka, Andhra Pradesh, part of Telengana and Maharashtra up to -100 mm for the period.
August September October (ASO) – Maharashtra, Telegana, Andhra Pradesh and Karnataka up to -100 mm for the period.
September October November (SON) – Central and western India, eastern states and entire Gangetic region up to -50 mm for the period.

Rahul Goswami

Vidarbha’s monsoon secret comes out in our innovative new rainfall index

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Monsoon rains in Vidarbha better than the rains in Konkan Maharashtra? How can this be possible? Especially when the average rainfall for the seven districts of Konkan Maharashtra, over 1 June to 9 August, is 1,812 mm and the average rainfall for the 11 districts of Vidarbha Maharashtra is 427 mm over the same period?

The measure that we are piloting is not based on the cumulative totals, for each district during each week of monsoon 2017, but for how adequate the rainfall has been over each week. What does that mean? Maharashtra’s Konkan region receives over four times the amount of rainfall that Vidarbha does. This does not mean that Vidarbha is more ‘rain poor’ than Konkan Maharashtra. The two meteorological regions are different just as their agro-ecologies, soils, water retention structures and flora are different.

Because of this difference, it is more useful to us to judge how adequate rainfall has been over any given period of measurement. We have taken a week because that is what we have data for, as provided by the Department of Hydrometeorology or the Department of Agricultural Meteorology of the India Meteorological Department, Ministry of Earth Sciences.

If you examine the cumulative totals – this means the running totals which from one week to the next carry over extras or deficits – the picture is as follows. One district only (Mumbai City) of the seven in Konkan Maharashtra is deficit (with -22%), all the rest being ‘normal’ in the range of -19% to +22%. The cumulative measurement picture for Vidarbha is this: only four out of the 11 districts (Buldana, Gadchiroli, Nagpur and Wardha) are ‘normal’ and in the range of -15% to -19%. The remaining seven are ‘deficit’ in the range of -23% to -36% (Amravati and Yavatmal being the lowest).

The weakness of the cumulative measure is that it ‘carries forward’ deficits and surpluses. A deficit in weeks 3 and 4 can be ‘made up’ for by better rains in week 5 and 6. But when rain in weeks 3 and 4 are important for a particular phase of a crop’s growth, the surplus that follows is of little use.

That’s where this pilot measure, what I have called the ‘rainfall adequacy index’, comes in. It indexes normalcy and variation from normalcy, plus or minus, and so records how adequate every week has been for the district. Using this method, we find that among Maharashtra’s meteorological regions, it is Vidarbha that has done best over 1 June to 9 August, followed by Konkan Maharashtra, then by Madhya Maharashtra and with Marathwada last.

The footnote is that the three districts with the best ‘rainfall adequacy index’ over this period are, in order, Sindhudurg, Nagpur and Wardha. The three districts with the worst index are Osmanabad, Nashik and both Thane and Palghar.

– Rahul Goswami

Rain for the Rani

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We find that the heavy rains that soaked the north Gujarat plains on the night of 1/2 July are testimony to the genius and far-sightedness of the builders of the Rani-ki-Vav, the famed stepwell which was initially built as a memorial to a king in the 11th century AD. The central heavy rainfall zone was immediately to the north-west of Patan, the town nearest to the Rani-ki-Vav, and it is precisely for this sort of rain that this fabulously constructed stepwell was built.

 

 

 

 

 

 

 

 

 

 

 

 

A typical June for the 2017 monsoon

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Three weeks of rainfall during the ‘official’ monsoon (which both within meteorological circles and outside is still said to begin on 1 June) season, we are now able to present the week by week trend.

The graphic (click for full size image) shows the distribution of districts according to our expanded measure for rainfall adequacy. We call this expanded as it has 12 categories (11 plus ‘no data’) which we debuted in 2015.

To be used mainly as a planning and response indicator – such as preparing for the consequences of a dry spell or readying contingency plans if continued heavy rainfall make flooding a likelihood – our expanded measure also provides a weekly snapshot of rainfall at the district level. These snapshots, which in the graphic take the form of coloured horizontal bars, when stacked together give us a trend.

The indiaclimate visualisation of rainfall distribution by districts using our 12-grade category scale.

What we see from the bars that represent district rainfall distribution for three weeks is that the 2017 monsoon has for this period been what the India Meteorological Department first forecast in April, and then confirmed in May: that this year’s monsoon will be normal.

In each horizontal bar the most important category is the one marked “+10% to -10%” as this is the ‘core’ normal range of 10% above and below the long-term average. Since our time-frame for each snapshot is one week, this means the long-term average rainfall for a district for that week. Next in importance are the two categories that follow, above and below. These are the “-11% to -20%” and “+11% to +20%” and may be interpreted as satisfactory.

Thus we see that for the week ending 07 June (the lowest bar) 41 districts recorded normal rainfall for that week, 22 recorded satisfactory (but below normal) and 15 recorded satisfactory (but above normal). The similar distribution the following week, that is ending 14 June and the middle bar, was 39, 26 and 11. And the distribution for the latest week, that is ending 21 June and the top bar, is 61, 35 and 21.

However as the monsoon has weakened over the last few days and may not regain its customary vigour for this time of the year until 27 or 28 June, we expect our next instalment to show more districts in the browner shades towards the left of the categories bar.

You can follow our monsoon data, graphics and commentary on both our website and twitter channel.