10 years of alternating rain, drought and shifting Seasons

Hi Subbu, I heard there is continuous downpour in Nanguneri (near by town which is 10 Km west of my farm). Is there rain in our farm ?.  No sir, nothing. The climate is as dry as it was for the past many days. There is no sign of any clouds.

Not my farm, but nearby

This is very natural and is expected in my farm. From my farm you can see the beautiful western Ghats silhouetted against the horizon.  You can also see wandering thunder clouds pouring rains over distant village. You can even smell rain. That is about it. The farm is neither near any mountain, nor near the sea. There are no water bodies or forest nearby. It is in rain shadow region.  No wonder it is a DRY LAND.  That is the challenge.

While thinking of this and browsing the internet, I came across some very useful first hand information in the net. Further analyzing the data I could prepare some useful notes.   Generally the rain, reservoir and meteorological data are not made available to public.  They are maintained in manual registers.   All measurements are monthly average rainfall in mm. i.e., amount of rain falls in a month.

I have selected three towns which are to the East, West and South of my farm land for the presentation here from the available data.  Of these the south town Radhapuram may experience more rain due to its natural position.  It lies ahead of a gap in western Ghats mountain range.  The other two towns mimic climate that of the farm.   

Tamilnadu  Anuual Rainfall.

The below graph must give an indication of what I can expect for myself.  Reference table above shows Tamilnadu State average rainfall.  From this we come to know that the state gets 81 mm rainfall every month on an average.  That should be our benchmark.

Comparing this with monthly rainfall average for over 11 years between 2000 to 2010 in three towns around my farm, clearly shows I can expect a decent rain of above 80mm/month only for 4 months.  

Strictly March, April and then October and November. This year there is no rains till now. The situation will become worse and will pickup only in September.  It is going to be a challenge to store the rain water for entire year in such narrow window.  the rain-fed crops can be sown only for one quarter which is the last quarter. I also hear that there is a shift of this rainy season to the right due to global warming. The second quarter rain is not guaranteed.

How does the climate change over a period of time ? 

A yearwise trend clearly shows that the volume of rainfall / month varies every alternate years.  There is a rhythm. One year dry and one year wet. If one year is 80mm/month the other year is only 40mm/month. There is also some flooding observed in 2008 and has upset the cycle, but is catching up.

This means that if this year is drought, we can recover next year and can expect dryness subsequent year. But this is a gamble. What if the subsequent year also happens to be dry ?

We hear that the el-Nino prediction for this year is not so great. Past year had been dry. Therefore I am hoping this year will be wet except for el-Nino factor. We expect the current year also will be dry only if we read the early warnings like the one below.

"Since 1951, the country has had 13 drought years (during SW monsoon), of which 10 have been during El Nino. The current patterns of El Nino are similar to the year 1968. "That year, there was a deficit of 11%. But this year, given local factors, we predict a deficit of 6% across the country," said Palawat"

Happy Farming.

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Credits:

State Ground and Surface Water resources data centre

http://www.igu.in/17-4/2paper.pdf

http://timesofindia.indiatimes.com/city/chennai/El-Nio-may-hit-cauvery-delta-with-drought/articleshow/33840746.cms