In a first, the effects of land moisture on monsoon studied

THE TEAM STUDIED THE ROLE OF MOISTURE TRANSPORT FROM LAND AND OCEAN IN ACTIVE AND BREAK PERIODS

MUMBAI : There could be an answer as to why rain forecasts sometimes go awry.

In a first, researchers led by the Indian Institute of Technology – Bombay (IITB) have found that land-based moisture is as important a determinant as moisture from the sea that influences monsoon and widespread extreme rain events over central India – from Gujarat to Assam – that also includes Mumbai.

A four-member team, based on data between 1980 and 2014, studied the role of moisture transport from both land and ocean in active and break periods during the monsoon which has implications for Kharif crops.

A monsoon active period is when there is more than above average rain for a minimum of three consecutive days; break period is when there is less rain for three consecutive days.

Researchers said active and break periods in India are characterised by two things – east-west and north-south asymmetry.

Describing their east-west asymmetry finding as “important and interesting”, the study found that the Ganga basin produces a lot of moisture during the monsoon due to evapotranspiration from dense vegetation and agricultural land. As a result, during the active period this moisture along with winds gets dissipated only over the Central Indian region resulting in high rainfall. However, during the break period, high speed winds transport the moisture that gets evaporated from the Ganga Basin leading to rainfall over northeast.

In contrast, the north-south asymmetry means when the Central Indian landmass receives good rain, the Indian Ocean does not – and vice-versa.