Another deficient monsoon 2004 - A comparison with drought year 2002 and possible causes

The rainfall over India as a whole during the summer monsoon season of 2004 was deficient with –13% below normal. Earlier in 2002, India has faced another worst situation when large-scale drought occurred and all India rainfall was below –19%. In the present study, we have compared briefly salient observational features of both the monsoons to find out their distinct characteristics. Comparisons show appearance of many similar as well as contrasting features. Though, both seasons were deficient, their dates of onset of monsoon over Kerala were either before or near the normal date. Progress up to central India was also normal in both the seasons. While Indian Summer Monsoon Rainfall (ISMR) during June was good, a few longest stagnation periods during advancing stage in July of both the years made unexpected delay of monsoon in covering entire India. Rainfall of July also suffered the most in both the seasons with a record lowest ISMR in 2002. Not a single depression formed in 2002 while in 2004, their frequency was less than half of normal. Analysis of other large-scale monthly anomalous ocean and atmospheric conditions over Indo-Pacific region including El-Nino conditions confirms that ENSO and Equatorial Indian Ocean Oscillation or EQUINOO have caused drought in July 2002, but not in July 2004. This is because very high typhoon formation and their recurvature with significantly higher than normal convection over northwest Pacific associated with record lowest ISMR in July, 2002 in contrast to occurrence of deficient ISMR in July 2004 which was associated with few typhoon formation and less convection. Also in 2002, Indian region was happened to fall exactly under the subsidence branch of Walker circulation with ascending branch over the western Pacific in the season in contrast to 2004, when subsidence was observed to be both over large part of western Pacific and adjoining Indian region.