Un­mask­ing the mon­soon

Putting to­gether the finer pieces of the mon­soon puz­zle re­mains a chal­lenge as new key driv­ers have emerged

Down to Earth - - FORECASTING -

But who wants to be fore­told the weather? It is bad enough when it comes, with­out our hav­ing the mis­ery of know­ing about it be­fore­hand.” This charm­ing piece of dry Bri­tish wit from the pen of Jerome K Jerome mocks the weather-ob­sessed Brit, and it may even amuse ur­ban In­di­ans, who ev­ery scorch­ing sum­mer, sub­mit them­selves to the tan­ta­lis­ing tease of the mon­soon rains. But for the mil­lions of poor In­dian farm­ers, whose lives de­pend on not only gen­er­ous but also timely rains,Jerome’s wit might ap­pear a tad too blithe, even rude. The re­cent ill-timed hail­storms that dec­i­mated crops of thou­sands of un­sus­pect­ing farm­ers in north and west In­dia un­der­score the ab­so­lute im­por­tance of fore­knowl­edge. If truth about the mon­soon could be fore­told, the In­dian farmer would be cer­tainly bet­ter off.

So come April ev­ery year, In­dia’s of­fi­cial weather tracker, aka the In­dia Me­te­o­ro­log­i­cal Depart­ment (imd), goes into a tizzy try­ing to an­tic­i­pate—with the help of reams of weather data, com­plex math­e­mat­i­cal mod­els and brute com­put­ing power, not to men­tion a bit of gam­bler’s gump­tion,for­ti­fied by a sense of history—whether the mon­soon is go­ing to be nor­mal,gen­er­ous or miserly.

A sea­sonal or long-range forecast (lrf ), as it is com­monly called, only gives the odds for the quan­tum of to­tal rain­fall from June to Septem­ber.Al­beit of no prac­ti­cal use to an in­di­vid­ual farmer’s sow­ing de­ci­sions, it is, nonethe­less, a por­tent of hope, or pos­si­ble gloom,for the na­tional gdp and the agrar­ian econ­omy.

imd pro­vides lrf for the In­dian mon­soon rain­fall in two stages—first,in the third week of April,and then in the sec­ond week of June.Along with th­ese,imd also is­sues monthly fore­casts for July and Au­gust for the coun­try as a whole.

Con­ven­tion­ally,lrf is made us­ing sta­tis­ti­cal mod­els, which har­ness his­tor­i­cal data to as­cer­tain In­dian mon­soon’s re­la­tion­ship with a host of at­mo­spheric


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