The anomalous weather parameters that lead to the extreme rainfall of Kerala in August 2018

Abstract

Extremely heavy rainfall occurred over Kerala, southwest coast of India, during mid-August 2018 resulting in devastating floods. This flood may be called “the flood of the century” as the state has not experienced a flood of this magnitude since the 1924 flood. The rainfall over Kerala during June, July and August 2018 was 15%, 18% and 164% above normal. To examine the reasons for this anomalous phenomenon, the meteorological conditions during this period are studied by analysing different parameters, such as wind, rainfall, potential evaporation, latent heat, outgoing longwave radiation, etc., and it is found that a combination of several rain favouring conditions prevailed at that time. The positive phase of Madden–Julian Oscillation (MJO) coupled with a monsoon depression in the Bay of Bengal and a weak trough in the south-eastern Arabian Sea strengthened the monsoon Low-Level Jet (LLJ) bringing moisture-laden winds over Kerala. The rising limb of Walker and Hadley circulations was also found over Kerala, which gave favourable updraft for cloud formation. In addition, the core of the Tropical Easterly Jet (TEJ) was found over the Kerala and Karnataka region. The cyclonic circulation in the mid-troposphere observed around the monsoon depression extended up to the west coast of India. Spatial variation of different weather parameters and their anomalies showed that many of the parameters were anomalously high during the second week of August 2018, when the torrential rainfall occurred. The simultaneous occurrence of all these conditions could have contributed to the extreme rainfall events and severe floods over Kerala.