What can cause a drought in India? Meteorologists till now were familiar with the warming of the Pacific waters that cause drought. This phenomenon is called El Nino. Recently, the Bangalore-based Indian Institute of Science (IISc) has found that surface temperature anomalies of the Indian Ocean can influence monsoon rains and can even cause drought as was in 2002.
PN Vinayachandran of IISc Centre for Atmospheric and Oceanic Sciences speaking at the 96th Indian Science Congress said, "The temperature distribution in the Indian Ocean, unlike that of the Atlantic and Pacific oceans, is characterized by warmer water on the western side and cooler water on the east. This is primarily due to the huge coastal up welling in the system in the western Arabian Sea. During certain years, the equatorial Indian Ocean presents unusually cold surface temperature anomalies in the east and warm anomalies in the west known as Indian Ocean Dipole (IOD)." An IOD phenomenon was discovered in 1999.
According to Vinayachandran, IOD is seasonally phase-locked and the anomalies appear in the period August-December. Atmospheric convection during IOD years is enhanced over the western equatorial Indian Ocean and suppressed over the eastern side. When winds blow from east to west along the equator, equatorial jets in the Indian Ocean reverse their direction, oceanic thermocline shallows in the east, coastal upwelling strengthens along the coast of Indonesia and biological productivity increases in the eastern side. Being a coupled ocean-atmosphere phenomena, the IOD affects weather and climate of countries bordering the Indian Ocean. Indonesia and Australia face drought while Africa and India receive excess rainfall in IOD years.
"The reverse of this phenomena occurred in 2002 which led to the worst drought of the century in India," he said. Similar conditions caused drought in 1972. In 2003, IOD phenomena were seen developing, but it did not develop to the full. Recent occurrence of IOD was in 2006, which gave good rains in the monsoon. Vinayachandran said that more research should be done to know more about the behaviour of the Indian Ocean.