Frequency and Magnitude of Heat and Cold Waves over India

Abstract

AbstractHeat waves (HWs) and cold waves (CWs) are well-known forms of extreme weather events. The observed frequency, magnitude, and duration of heat waves (HWs) and cold waves (CWs) over the Indian main land have been studied. For this daily maximum temperature of 103 stations during the hot weather (AMJ (April–June)) season for the period 1961–2020 and daily minimum temperature data of 86 stations during the cold weather (DJF (December of previous year to current year February) season for the period 1971–2020 were used. The trends in the seasonal frequency of these extreme temperature events as well as their association with the ENSO events have also been examined. During the AMJ season, HWs are generally experienced over the north, northwest, central, east India, and northeast Peninsula [together called core HW zone (CHZ)] with the highest frequency during May. Noticeable increase (decrease) in the frequency and spatial coverage of HW/SHW days compared to their climatological values were observed during the El-Nino (La-Nina) years. There are significant increasing trends in the HW/SHW days at most of the stations from CHZ. The total number of HW/SHW days over CHZ showed noticeable increase during the recent decades 1991–2000, 2001–2010, and 2011–2020 compared to the previous three decades. During DJF, the CWs are generally experienced in the core CW zone (CCZ) that is nearly the same as CHZ with the highest frequency during January. Noticeable decrease (increase) in the frequency and spatial coverage of CW/SCW days were observed during the El-Nino (La-Nina) years compared to their climatological values. The total number of CW/SCW days over CCZ decreased during the recent decades, namely, 1991–2000, 2001–2010, and 2011–2020 as compared to the previous two decades. However, the areas of CW days of ≥8 days on an average increased over north along the plains of Himalayas and central India in the latest decade (2011–2020) as compared to the previous decade (2001–2010). This study coincided with the fact that the latest three decades were the warmest decades for the country as well as for the globe. Associated with intense and persistent extreme temperature events, large human mortality was reported during some years of the study period. India Meteorological Department has recently established a seamless forecasting strategy from short-range forecasts to seasonal forecasts for HWs and CWs. With this new development, IMD is able to forewarn the agencies and people and save thousands of lives.KeywordsHeat wavesCold wavesTrendsClimatologyEl Nino/La Nina