Recently, heatwaves in India, occurring during the Indian summer season of April and May are increasing and causing unprecedented number of deaths. A heatwave is a period of excessively hot weather accompanied by high humidity leading to a risk of life. For example, severe heat waves resulting in thousands of deaths of humans and livestock were reported around the eastern Indian state of Odisha, in 1998, Andhra Pradesh in 2003 and Ahmedabad and other parts of western Indian state of Gujarat in 2010. Also, a particularly major heatwave affected large parts of India and Pakistan claiming as many as 3500 lives in 2015. Even globally, world health organization (WHO) noted that more than 1. 6 lakh people died due to severe heat waves during the period 1998 to 2017.  Thus, severe heat waves are a major calamity caused due to climate change as explained below.

Temporaldistribution of 2m-Air temperature anomalies in the Arctic region during1900-2020 period using various global datasets. 

In a recent study involving researchers from India and Brazil published a research article entitled “Large-scale connection to Deadly Indian Heatwaves”. In this study they showed convincingly that deadly Indian heatwaves occur due to a theoretical mechanism called “Quasi-Resonant Amplification (QRA)”. In this mechanism, the so called planetary Rossby waves amplify by resonance when the free Rossby waves (generated due to rotation of earth, discovered by C. G. Rossby in 1939) and forced Rossby waves (forced by earths topography, discovered by Charney and Eliassen in 1949 or heating discovered by Smagorinsky in 1954) coincide in their horizontal scale, called wave length. Which is related to the number of these waves around a latitude circle.

Mortalitydue to heatwaves in India from during 2000 –2015 period

Recently, Arctic region is warming at an alarming rate, leading to what is called “Arctic Warming”. In the Arctic region, temperature is increasing more than twice as fast as the global average!!!  Arctic warming is a result of “global warming”, this arctic warming reduces normal equator (a hot region) to pole temperature gradient, because normally arctic region is very cold. Decrease of temperature gradient favors decrease of zonal wind (wind from west to east, which occurs in the mid-latitudes) and its vertical shear (because of so called thermal wind relation). A decrease of zonal wind favors in some special conditions (which are becoming more frequent recently) an increase of Rossby wave amplitudes for some wavenumbers or the QRA. The positioning of amplified Rossby waves is such, that in some specific locations (over India) a high-pressure cell occurs, leading to sinking motion and increasing surface temperature drastically. This increase of surface temperature causes heat waves.

Surfacemaximum temperature (◦C at 2 m) for the three cases: (a) climatology(1979–2018), (b) 2010events mean, (c) 2013 events mean, and (d) 2015 events mean of heatwaves     

Although, this QRA mechanism is shown to be the cause of 2003 European heatwave and 2010 Pakistan flood and Russian heat wave and other extreme events affecting human and animal life, Dr.V. B. Rao and co-authors have shown for the first time that, heatwaves leading to deaths, can occur in India, due to QRA, caused by arctic warming a result of global warming. Indeed, several authors have shown that Indian heat waves are increasing, but a possible cause is global warming Thus there is an urgent need to plan mitigation of this very adverse climate change. Dr. V. B. Rao and others have suggested in their article, that Indian heatwaves can be predicted about ~4 days in advance prior to their occurrence.

Mr. Govardhan Dandu

The results of this study were published in  reputed British journal, Quarterly Journal of Royal Meteorology. Dr. V. B. Rao, National Institute for Space Research, INPE, Brazil, Dr. K. Koteswara rao (corresponding author from Azim Premji University), Dr. B. Mahendranath, (Andhra University), Dr. T. V. Lakshmi Kumar (SRM Institute of Science and Technology), and Mr. Govardhan Dandu (University of Hyderabad, a Ph.D. student).