A lot is being said about the failure of the south west Monsoon in the southern regions of the country especially in the sub divisional zone of South Interior Karnataka.
Comparisons are being made between different zones as if data from a single year or a few years can be then used to make long term predictions.
I therefore present here an analysis of long term data that has been taken from the year 1871. It is up to the year 2014 and taken from the website of Indian Institute of Tropical Meteorology.
I have compared the sub divisional data of South Interior Karnataka (SIK) with that of Konkan and Goa(K&G).
The above chart represents the range of percentage variation between the monsoonal rainfall of SIK and K&G. This ranges from between 42% which was the highest in 1941 and 12% which was the lowest in 2003. (42% here means that SIK received 42% of what K&G received and therefore is a good number as against only 12% which it got in 2003)
I present a summary of some important observations;
The ten best years since 1871 are as follows..1941 (42%) , 1986 (36%), 1899 (34%), 2009 (33%), 1968 (32%), 1906 (32%), 1920(32%), 1889 (31%), 1912 (30%), 1882 (30%).
The ten worst years since 1871 are as follows..2003 (12%), 1934 (12%), 1976 (13%) , 1875 (13%), 1970 (14%), 1990 (14%) , 1955 (14%), 1937 (14%), 1884 (15%), 1963 (15%).
(All percentages are rounded off to nearest decimal)
The average for the entire period is marked with a pink line on the chart which is 21.78%. That means on an average SIK receives about 22% of the monsoonal rainfall of K&G.
Now lets look at the figures for 2015 and 2016 as provided by IMD. In 2015 SIK received 30% of the rainfall of K&G. And in 2016 this was about 15%. Admittedly 2016 was a bad year for the whole of southern peninsula (Coastal AP and Telengana were normal).
And here is the most important finding....
The average percentage rainfall (SIK vs K&G) for the period 2000 to 2014 is 21.27% !!!!
This is just 2% below the long term average of 21.78%, well within the margin of error !!
And if we add the two IMD figures for 2015 and 2016 the average is 21.4% !!! This is less than 2% of the long term average.
So far this year up to 30th July 2017 the percentage is slightly over 12%. We wait for the final outcome in September.