Del­uge and deficit

The monsoon of 2017 has chal­lenged In­dia's con­ven­tional and sim­plis­tic def­i­ni­tion of the com­plex trop­i­cal cir­cu­la­tion

Down to Earth - - CONTENTS - SHREESHAN VENKATESH @shree­shanV

The 2017 In­dian monsoon is any­thing but nor­mal

IT WOULDN'T be in­ac­cu­rate to say that the 2017 monsoon has been all about floods. At least 11 states ex­pe­ri­enced floods since the on­set of the monsoon in June. Till the mag­a­zine went to print, 150 dis­tricts, or over a fifth of the coun­try’s dis­tricts, have re­ceived more than 100 mm of rain in a sin­gle day. More than 1,000 peo­ple have died and sev­eral mil­lions af­fected. The sit­u­a­tion has not abated.

But as we en­ter the fi­nal month of the monsoon, it would seem para­dox­i­cal to say that the monsoon of 2017 is also about a drought loom­ing over large parts of the coun­try. Around 40 per cent of the dis­tricts have re­ceived de­fi­cient rain­fall. Parts of north, cen­tral and south In­dia are about to face a drought. The dis­tri­bu­tion map is­sued by the In­dia Me­te­o­ro­log­i­cal De­part­ment (imd) shows a large cor­ri­dor of de­fi­cient rain­fall ar­eas (see map).

Con­sider this: only less than a fourth of the 400-odd weekly monsoon ob­ser­va­tions from June 1 at the 36 me­te­o­ro­log­i­cal sub­di­vi­sions recorded a nor­mal rain­fall. Yet, imd has cat­e­gorised all four ge­o­graph­i­cal re­gions within the mar­gins of a “nor­mal” rain­fall. That means ex­treme rain­fall for a few days has com­pen­sated—and in some cases over-com­pen­sated—for the strik­ing de­fi­ciency, in­di­cat­ing wide­spread im­bal­ances in rain­fall dis­tri­bu­tion.

Ra­jasthan is a glar­ing ex­am­ple of this im­bal­ance. In the third week of Au­gust, the state reg­is­tered an ex­cess of 20 per cent rain­fall. While west­ern Ra­jasthan, pri­mar­ily a desert, recorded an ex­cess of 58 per cent, eastern Ra­jasthan recorded 1 per cent deficit. Chandi­garh, on the other hand, did not get a de­cent spell of rain till Au­gust 21, and had a rain­fall deficit of over 24 per cent. The deficit re­duced to 8 per cent af­ter the city re­ceived heavy rain­fall on Au­gust 21. So sud­den and heavy down­pours are mark­ing the new “nor­mal”. Even Ben­galuru, which faced un­prece­dented floods re­cently, has a rain­fall deficit of about 8 per cent.

The Gu­jarat sub­di­vi­sion has seen four weeks where rain­fall ex­ceeded the nor­mal lev­els by more than 50 per cent, two weeks where it ex­ceeded the nor­mal by more than 20 per cent, and, five weeks where rain­fall was de­fi­cient by more than 60 per cent. So not a sin­gle week reg­is­tered a nor­mal rain­fall! Ditto for Suarash­tra and Kutch.

In stark con­trast, the rain-rich re­gions of Ker­ala and coastal Kar­nataka re­ceived de­fi­cient rain­fall, while the rain shadow re­gion in south­ern Tamil Nadu re­ceived rain­fall far above the nor­mal, thanks to heavy down­pours in Au­gust.

In drought-prone Marath­wada and Vi­darbha, the deficit stands at 32 and 28 per cent, de­spite strong pre-monsoon show­ers. Farm­ers in the re­gions have faced heavy deficit in seven of nine weeks—five of which recorded more than 60 per cent rain­fall de­fi­ciency. De­spite a third wave of floods, As­sam has recorded a near nor­mal rain­fall. And while Tripura and Mi­zo­ram have re­ceived ex­cess rain­fall, Ma­nipur and Na­ga­land have suf­fered heavy deficits.

Whole­sale fore­casts?

Since April, imd has been say­ing in all its fore­casts that it will be a nor­mal monsoon this year. But the per­for­mance of the monsoon can no longer be only ac­counted by the amount of rain as ex­treme rain­fall days are in­creas­ing, trig­ger­ing floods and crop dam­age. A “nor­mal” monsoon should take into ac­count the chang­ing dis­tri­bu­tion pat­terns as well as at­mo­spheric con­di­tions. Only such fore­casts will be able to pre­dict floods as well as help farm­ers know when to sow.

There are damn­ing er­rors too. For in­stance, pre-monsoon show­ers in Marath­wada and Vi­darbha were an­nounced as “mon­soonal rains” in the be­gin­ning of June. Thou­sands of farm­ers, who un­der­took sow­ing fol­low­ing the an­nounce­ment, now stand to lose their crops fol­low­ing heavy rain­fall deficits in the sub­se­quent weeks.

In­cor­po­rat­ing wind di­rec­tions in its fore­cast and as­sess­ment method­olo­gies would have en­abled imd to make an ac­cu­rate pre­dic­tion. An­other at­mo­spheric pat­tern that in­flu­ences the monsoon, but finds lit­tle men­tion in imd’s as­sess­ment is the west­ern dis­tur­bances. It usu­ally ar­rives in Au­gust but this year it ar­rived in July, caus­ing heavy rain­fall in sev­eral parts of north, north­west and cen­tral In­dia.

It is time, the imd de­fined its new “nor­mal” as floods are tak­ing a heavy toll on lives and prop­erty across the coun­try. Mean­while, farm­ers else­where await an­other year of drought.

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