A Dry June in 2012 – Why Bangaloreans Shouldn’t Worry.

It’s the end of June, and Bangalore has received very little rain till date. The monsoon so far has turned out to be a not-very-damp squib. There is a lot of concern and worry among people as to what this portends for the rest of the season and year.

I maintain that now isn’t the time to worry, but instead it’s time to prepare for the monsoon.

Rainfall this June in Bangalore has been quite dreadful, with Bangalore getting only 13mm of rain till the 25th of June, against a monthly average of 80mm. and even that in small, scattered showers of 1-2mm. The lowest rainfall ever received in June was in 1945, when Bangalore got only 4.5mm. June 2012 does not fare much better. When June numbers are laid out in ascending order as below, you can tell quite clearly that 2012 is in the bottom 5 percentile when it comes to June rainfall. Pending copious rain in the next couple of days, the quantity is dreadfully low and there aren’t two ways to see it. Farmers close to town without irrigation facilities would have no doubt suffered. Lakes and the water table will also have to wait to get recharged.

However, what does this mean for the year? To begin with, June is only the sixth wettest month for Bangalore. We get more rainfall during all other months between May and October. June, on average, contributes less than 10 percent of annual rainfall. That being said, it’s useful to check if there is a correlation between rainfall in June, and rainfall annually. That is, it’s important to investigate whether deficit rains in June imply a drought year.

Turns out that the answer is a resounding NO. Below is a plot of Annual rainfall versus June rainfall. If the two numbers were linked positively (or ‘positively correlated’), an increasing trend would have been seen on the graph. Instead what is found are data points scattered all across the board. The three encircled points are from the three years that received lesser rain in June than 2012. Only one of them is a drought year, while the other two appear to have received over 1000mm, more than the annual average.

There you have it. June is not the most consequential of months for Bangalore. Bad rains in June alone are not sufficient cause for Bangaloreans to worry. What each of us could do on our own is prepare our houses and buildings to harvest the rains that we are certain to get over the next few months. The onset of the monsoon, if nothing else, cooled Bangalore down for good. Rejoice, for the summer is over, and await the rains to come.

Written by Pavan Srinath.

Data used in this post is from here and here. June rainfall for the year 2001 is missing. The number used for June rainfall in 2012 is the sum of what was received between June 1 and 26, as collected from IMD’s automated weather station in Bangalore.

Update: June 27, 2012. 10:50 AM.
Karthik has an excellent graph of June rainfall versus rain from July-October that underscores what was said on this post. Click on it to view it in full size.

Update #2: June 27, 2012. 1:47 PM.

Karthik also has a similar graph for all of India, which tells the same story: that rainfall in June has no bearing on how much it would rain across the country during the monsoon. While scanty rain in June across much of India (except the north east and the western coast) has caused stress for farmers and others, it does not imply that the rest of the monsoon will necessarily be bad. What it does, however, is place a lot of importance on rains over the next few weeks. The IMD has released coarse-grained forecasts for the season which says that the monsoon this year will be normal or a little below normal for all parts of the country other than the North East. The accuracy and the limitations of this forecast will be tested over the coming months.

5 Comments

  1. Excellent post. Now the key questions.
    1. When would the rains have to fail for Bangaloreans to be worried ? Is it the rainfall of August or September ?
    2. Since the September-October rains which contribute almost 40 % of the rains to the fair city are actually from the NE Monsoon how is June which is the SW linked causally to the NE Sept- Oct ones?

    In any case your recommendation of being prepared to harvest rain is welcome. In fact it is in the years of less rain that the collection becomes more important.:)

  2. Thanks!

    Much of the rain we get in Bangalore is from the SW Monsoon. The NE Monsoon sets in on the Bay of Bengal coast only around October 15-20, so the rains after that could be classified as the NE Monsoon rains, not before. The IMD, out of convenience, labels Jun-Jul-Aug-Sep as the summer monsoon months, and Oct-Nov-Dec as the returning monsoon months. The actual monsoons don’t give a whit about when a month begins. :) A useful frame to think in terms of would be: “It rains in Bangalore as the monsoon starts retreating from the north of India”.

    It’s largely an academic exercise, but I want to calculate how much rain Bangalore gets from the summer (ie before monsoon onset), SW and NE monsoons using real onset and withdrawal dates… it’s in the pipeline. :)

  3. All that being said, the question that begs a very serious answer is Q1: When should we worry? On what basis should we worry? That, I hope, will be something that I and others start exploring in depth.

    Data analysis apart, “Worrying” is objectively useful only when it spurs us to action, or acts as a precursor to it. Timeliness of information that either causes or assuages such worries is paramount: if one gets information in March about failing rains in August, that’s one thing… it is something one can act on. If I learn through data only in November that the ongoing year is terrible, it’s completely useless. :)

    So the idea is to find ‘teleconnections’ in the climate data that provide useful information in advance. Hope something turns up. :)

  4. Pavan, You must have seen this in DH yesterday – they have the opposite view and mention this research project. Did you update your ‘no worry’ status to ‘worry’ status? :).

    http://www.deccanherald.com/content/263010/no-shortage-problems.html

    Lalita

  5. Its Closing to October already.. and we know how much rain we’ve had in Bangalore! Guess you should be changing the title of the article?

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