Friday, September 23, 2016


Yesterday in the comments section I gave a brief analysis of "Peninsular" rainfall for the period 1871 to 2014 during the monsoon months, June to September.

Today we look at the same set of data ((via IITM under the All India and Macro Regional data set. (It includes six subdivisions namely Coastal Andhra Pradesh, Rayalseema, TN & Pondicherry, Coastal AP ,S I Karnataka and Kerala)) of the "Peninsular" rainfall for the period October to December.

This period is normally classified as the NEM and this is what IMD Chennai says about it..
"The period October to December is referred to as Northeast Monsoon season over peninsular India. Earlier   this period was also referred to as 'Post-Monsoon Season' or 'Retreating southwest Monsoon Season'.
Northeast Monsoon season is the major period of rainfall activity over south peninsula, particularly in the eastern half comprising of the meteorological subdivisions of Coastal Andhra Pradesh, Rayalaseema and Tamilnadu-Pondicherry. For Tamilnadu this is the main rainy season accounting for about 48% of the annual rainfall. Coastal districts of the State get nearly 60% of the annual rainfall and the interior districts get about 40-50%  of the annual rainfall. 
Though the principal rainy season for  Interior Karnataka, Kerala and Lakshadweep is the Southwest Monsoon season, rainfall continues till December in these sub-divisions, the period October-December (Northeast Monsoon ) contributing about 20 % of the annual total. " 
First we look at a graphical representation of the raw data from 1871 to 2014..

As can be seen the rainfall varies from as low as 93mm in 1876 to 585mm in 1946. Those are the extremes. The average for the entire 144 years is 345mm.
Now we look at a smoother version of the above data which has been averaged every three years..
 As can be seen there is a cyclical behavior that seems to swing between highs and lows every few decades. The lows are formed every 35 to 45 years and since the last one was in 1990 the next can be expected around 2025 to 2035 (since it is averaged for the previous three years the actual lows might form from 2022-25 or 2032-35).
An even more smoother version (9 years) gives us this ;
 Here too we get the same 35 to 45 year lows in rainfall.
We now compare the Peninsular Oct to Dec rainfall to the Annual Peninsular rainfall for all the years;
(smoothed every nine years)

Same conclusions as above!!! Also the range varies from 35% (1888) to 25%(1955).
And finally we compare the Peninsular Oct to Dec rainfall with the Peninsular Monsoonal rainfall;
(smoothed every nine years)
Again the same conclusions as far as the lows are concerned. The range varies in this case from 65%(1888) to below 45%(1912,1955).
Conclusions: The Peninsular rainfall from Oct to Dec shows a huge variation from 93mm to 600mm and ranges between 25% to 35% of its annual rainfall averaging around 29.5%. As compared to the south west Monsoon it varies from below 45% to almost 65% averaging around 54%. A cyclical behavior is very evident in the charts above and the current century shows nothing unusual.
The fact that some kind of regularity has been seen in the trend for the last 144 years does not suggest at all that a new trend might not emerge in the future..weather is too complicated for any one to truly predict accurately a hundred per cent all the time. I personally feel a time period of 150 years is too short for any kind of definitive trends to be emerge.

 

((Thanks to IITM for the data and IMD Chennai for the NEM introduction)) 

46 comments:

Vinod Desai said...

Great information. I like this blog for such awesome information/analysis the readers have been getting over the years.
Thanks for compiling and sharing.

sset said...

IMD red alert for konkan.... looks like for MAHA 3 digit rains are like 1 digit rain...

pounding rains (taken from kea blog)
Maharashtra rainfall (mm) :
Bharne - 347
Lamaj - 323
Khed - 297
Ambavali - 257
Mhasala - 244
Devhare - 229
Palgad - 212
Roha - 211

rajesh said...

superb work GSB...what an effort...praiseworthy.

rajesh said...

On Friday morning, Mumbai had a thunder shower. So, Friday morning readings saw Scruz getting 40 mms and Colab 45 mms in last 24 hrs. In line with Vagaries 40-60 ms estimate for the same period.

rohit aroskar said...

Very nice analysis..GSB sir

Hrishikesh said...

Do we expect thunderstorms in Mumbai today?

Nilay Wankawala said...

Lovely Trend Analysis- good informative article and yes conclusion is also Convincing -

sridhar. rajagopalan said...

Rajesh, just wondering what caused so much rainfall the last couple of days,without any UAC or low, in place and i guess it rained much more than the previous days where UAC was very much prevalent... and also major rainfall in places like dahanu and vasai...while place like thane city not even getting fraction of that

Akshay Shah said...

It really takes a great effort GSB sir for such an analysis in a country wherein people are not having interest in learning / maintaining data about the weather. Really commendable. More so, I am sure that post monsoon, interest of general public is substantially reduced in weather and such is so cause monsoon is the lifeline of our country even today.

Vijayanand said...

Day2 of testmatch between India and Newzeland post lunch washed away by rain in kanpur. Hopefully next 3 days should be clearer.

Narayanan Ky said...

Very nice analysis of Cyclic characteristics of NEM can be good insight for water management and planning.

Sleepless said...

Great Analysis. I trust this blog more than any other source for Monsoon season.

GSB said...

Thanks Rajesh Sir and also all the others for your kind words...its very important that we keep a scientific and analytical worldview always in our interactions with whatever we are dealing with in our daily lives. The world has progressed immensly from the scientific method but it remains to be fully exploited by us here in India.

Looking at what has been achieved by other nations and the groups and communities they have developed, we still have a long way to go. Rajesh Sir has given us a platform which can help us build one such community in India. Hope we are successful in this effort.

sset said...

CFS model shows very weak NEM - similar to 2012 - disaster for southern india...Cauvery?
In few years linking of Cauvery with Maharashtra river may be required.

Anyway Rajesh sir has done very good work - "Time Series data modelling"

Cumulus Arjun said...

Dear SSET, looks like you are an enemy of south India. Please don't troll like this. Talk something rather meaningful

Cumulus Arjun said...

Sir, what is the forecast of the coming days for Mumbai City and Mumbai suburbs

Cumulus Arjun said...

I appreciate Vagaries for providing such a detailed analysis for not only NEM but also for other weather activities and seasons

rajesh said...

Arjun.... You asking for Mumbai Forecast. Forecasted till Friday in last blog. Let the forecast period end. I don't overlap unless there is change.

parshuram shinde said...

Thundering in santacruz

Cumulus Arjun said...

Okay sir. Very heavy thunderstorm here now (goregaon)

sset said...

No way I am from south India settled in beautiful green "Navi Mumbai" it is so contrasting here we non stop rains over our place (south india) all reservoirs that too south west -cauvery are completely dry - all are hitting dead storage.

Nilay Wankawala said...

It's raining cats and dogs since 8.00 pm borivali. Seems some one is sitting in sky throwing buckets and buckets of water from sky to earth. Thundering too.

Cumulus Arjun said...

Okay okay sset

Animish Masurkar said...

Streets are flooded in Mumbai andheri

rajesh said...

Torrential rains lashing Central Mumbai Now (22 hrs)...will give readings in an hour in Flash Snippet

Shreyas Dhavale said...

Very heavy rains (like July) have lashed konkan. Landslide reported in Parshuram ghat near Chiplun. Konkan railway shut due to water-logging on tracks. Heavy rains reported in Marathwada districts of Nanded, Latur, Beed and Parbhani.

Negative side: Heavy rains in mid/late September have damaged the crops which were in mature stage.

Positive side: Bountiful rains in Maharashtra have ensured that there will not be major water scarcity even in the interior areas.

Unknown said...

@sset : I am also from South but living in Mumbai for many many years. I love the charm and beauty of the SWM rains. But unlike you I do not keep parotting all the time about South India rains or failure and baselessly link it to SWM in every post. Thats why you are bringing a bad name to all sensible people here from the South. Infact why only South, I would say all sensible people.

Suresh

SVT said...

Some parts of Mumbai might get 150mm rains since evening. Getting impossible to forecast. Never seen such wet spell in September end before. Almost 700mm rains since thursday.

Cumulus Arjun said...

As per MCGM site, Dindoshi received around 17-20 mm in 15 minutes and around 60-70 mm in just an hour yesterday!

sset said...

Non stop torrential thunderstorms entire night over Navi Mumbai- September easily cross 1000mm!
For information -> Apart from Kerala,Coastal Karnataka,Malnad,Cauvery basin facing drought many Asian countries in similar latitude facing drought...
Sri Lanka tea production impacted,Malaysia,Thailand durian fruit production impacted...

http://economictimes.indiatimes.com/news/politics-and-nation/Cauvery-crisis-Cauverys-birthplace-Kodagu-stares-at-drought/articleshow/54308052.cms

abizer Kachwala said...

Whooping rains.....what is going on...floods in nagothane since friday .Today 3-5feet water.whats your forecast.pls tell soon.

SVT said...

So yesterday 165mm in Colaba and 93 in Santacruz. Every chance we got more rain in some places in South-Central Mumbai. Localised strong thunderstorm. 650mm rains last thursday.

SVT said...

Cumulus Arjun and others. Where exactly you guys getting local areas rainfall on MCGM site or their App? http://dm.mcgm.gov.in:8080/RESTFulWS/index.html# cant search area on this site. Any new link please.

sset said...

taken from kea blog...Looks like Nov also MAHA is going to be pounded!!
TN to be added to drought list.. GOD only can save! - entire south drought hit all because of this SWM!

24hrs pounding in MAHA
Maharashtra rainfall (mm) :
Shirgaon - 385
Murdav - 260
Kadwai - 247
Pen - 220
Washi - 220
Kamarli - 220
Roha - 216
Margtamhane - 215
Nagothane - 210
Devale - 207
Murud - 203
Dajipur - 200
Alibag - 192
Uran (Navi Mumbai) - 172

Nilay Wankawala said...

SWM brings rains to entire country- It can not be a source of DROUGHT

Saurabh Dwivedi said...

Hi SSET
Please do share your views on this blog. I have noticed that you do not comment on posts/comments that do not support your hypotheses. Some days back i pointed out that in Tamil Nadu last 9 out of 12 north east monsoons(up to 2015) have been surplus. Here is the link http://www.imdchennai.gov.in/nemweb.pdf . This link is up to 2014. 2015 was surplus for Tamil Nadu, every one knows that.

The northern half of southern India is getting pounded by rain for the last few weeks.
Here in Hyderabad schools are closed on and off, offices are disrupted, lakes overflowing, roads washed away.

Please do comment on this post as well my comment. Only if you engage with facts you can get people to agree with you. Right now you just share opinions based on no evidence.

Again i repeat based on evidence . 9 out of the lat 12 north east monsoons for tamil nadu have been surplus.
Regards
Saurabh

Avtansh said...

sset, trolls like you are the exact reason why we have issues in our country. The mindset of us vs them. Instead of finding any real solutions focusing on putting one region against another. Atleast leave nature out of your dirty politics.

I take strong exception to the language you use.
Only illiterate people like you will say incendiary stuff like south has a drought because of this swm and that Maharashtra will get pounded in November. Stop this rumour mongering and get a life.

Rajesh sir, I understand the need to have free comments. But this person who even refuses to divulge his identity seriously compromises the quality of learning/discussion on our forum. It is most unfortunate. Request you to filter comments as per your best judgement. I am confident if you do it a few times people will fall in line subsequently. Thanks.

Cumulus Arjun said...

SVT you rather download the app of the MCGM, you will get the rainfall amounts

Cumulus Arjun said...

SVT you rather download the app of the MCGM, you will get the rainfall amounts

sset said...

after long long long long time.............after long long wait.....after all hairs become white.....Bhagmandala cauvery receives 35 mm of rain !!!!!! (from MAHA angle it is just 1 drop!)

sset said...

It is only raining in southern indian places bordering Maharashtra or Orissa... 3/4th of southern india is dry...yourself will come to know next week in all headlines cauvery is completely dry...

Unknown said...

@sset : since you refer to kea blog all the time, can you please attempt writing such similar posts there since it is more based on south rains ? I assure you that in such case Pradeep John will suspend you from Kea. Recently there was a case when someone attempted to compare Mumbai rains with Chennai rains again and again. Pradeep issued a strong warning and to give credit to the other person he stopped doing so immediately. But you do not seem to be learning. Please do not take advantage of Rajesh's kindness to you and all of us. Rather than use that freedom constructively you are abusing that freedom. Please stop this immediately.

Suresh

MIRAL KALWADIA said...

rajesh sir, pls give your forcast for mumbai ...i will be in city for next 2 weeks ...waiting for your forcast !! :)

Vijayanand said...

Well said Suresh. But my friend, SSET will not stop his anti south india comments and also his writings would get published here. SSET would not last a day in keaweather. Dear Pradeep would first warn him and then ensure cheap comments do not get published.

Its just so sad. Dear rajesh sir's tolerance and kindness is being so badly misused by this chap.

One idea, rajesh sir can you please make it mandatory for people to register with their phone number here. Unknown identity makes it easy for people to write irresponsible stuff.

Nilesh Ladhad said...

Very localised rain in Valsad for the past few days,last rains of the season going on, I think. Hope the new system will bring atleast one heavy shower in Valsad. Please forecast for Valsad proper, sir.

rajesh said...

sset: All contributors to articles and comments put in a lot of efforts and hard work to substantiate their views.
Recently i noticed that your comments on this blog are getting a bit repetitive. Our readers our clever enough to understand and appreciate a point commented upon on publishing. Once a point is conveyed, it is well understood.But i notice your points are getting pessimistic and "head hammering." Vagaries being a free blog, I dont want to filter or censor any comment (I have not deleted any so far), but, this being an international blog, it should not be one of conveying a particular message or leaning towards one side.
Finally, I would like readers to put in their comments with their names,and not any initials or pseudo names. Becomes difficult to have a one to one interaction without the real name.