Assessing rainfall deficiencies in different parts of the country in the last 20 years and the severe drought years - 2002, 2004 and 2009 - in particular, the Pune-based Indian Institute of Tropical Meteorology (IITM) has developed an experimental model to forecast a possible drought by assessing imagery and data generated by satellite.

The 2009 drought and the failure of the South-West Monsoon may be due to some internal problems which might have crept into the system, apart from the known factors like the warming of the Pacific and Indian Ocean and the influence of the Eurasian snow cover, according to a team at the IITM.

“We have assessed the meteorological data of rainfall deficiencies in different parts of the country in the last 20 years. We also assessed the rainfall deficiencies in the years not influenced by El Nino (a phenomena caused by the warming of the Pacific Ocean). We also studied the influences of Indian Ocean Diapole, warming of Indian Ocean and came to the conclusion that some problems in the internal dynamics of the monsoon system are also the causes for prolonged dry spell,” said Dr R Krishnan of IITM.

He said that IITM will give this experimental forecast model to IMD. The IMD director-general, Ajit Tyagi when contacted said : “we will use this model from 2010.”

Dr Krishan is participating in the 97th Indian Science Congress

“Monsoon system is a complex interactive mechanism involving land-ocean-atmosphere correlation. When the moisture laden clouds enter the mainland it works according to its own mechanism. Sometimes the dry spells are lingered to the problems in the system and this causes drought,” he said.

One of the causes which disrupts the monsoon system identified by IITM is the entry of cold dry clouds from the mid-latitudes through the northwestern region of the country bordering Pakistan. In meteorological terminology it is called “westerlies”.

“These cold dry clouds suppresses atmospheric convection which leads to radiation going out to the outer space. The monsoon tough then shifts to the foothills of the Himalays and dry spell lingers,” said Dr Krishnan.

According to him in the Monsoon period in 2009 such a situation occurred and prolonged dry spell extended from India to South-East Asia also, while good rains took place in East Asia. Past data shows that in such a situation monsoon rains shifts to northeastern India and Tamil Nadu.#