Impact of El-Niño-Southern Oscillation (ENSO) on extreme temperature events over India

Abstract

In this paper we examine the impact of extreme phases (El-Niño and La-Niña)  of El-Nino- Southern Oscillation (ENSO) on the frequency, duration, magnitude and spatial coverage of Heat waves (HWs) computed using daily maximum temperature of 103 stations during the hot weather season (April-June or AMJ) for the period 1961-2020 and Cold waves (CWs) computed using daily minimum temperature of 86 stations during the cold weather season (December-February or DJF) for the period 1971-2020 from India. HWs are generally experienced over the north, north-west, central, east India and north-east Peninsula [together called core HW zone (CHZ)] with highest frequency during May.  Whereas, the CWs are generally observed in the Core Cold Wave Zone (CCZ) which is nearly the same as CHZ but includes Jammu and Kashmir and excludes coastal Andhra Pradesh. The study observed noticeable decadal variation in the frequency, spatial coverage and area of maximum frequency both in the HW/SHW and CW/SCW days over the country. It was also observed that there is an appreciable increase (decrease) in the number of HW days during El-Niño (La-Niña) events. Severe Heat waves were more prominent (longest and hottest) in El-Niño years. Exactly opposite association was observed in case of CW days. El-Niño event mostly inhibits the CW activities in India.  Significant increasing (decreasing) trends in the HW (CW) days were observed in many stations from CHZ (CCZ), which is in tune with similar trends observed over various other parts of the world.  The possible physical mechanisms for the observed linkage of these temperature extreme events over the country with the El-Nino / La-Nina are also discussed in the paper.