Anatomy of Indian heatwaves

Abstract

India suffers from major heatwaves during March-June. The rising trend of number of intense heatwaves in recent decades has been vaguely attributed to global warming. Since the heat waves have a serious effect on human mortality, root causes of these heatwaves need to be clarified. Based on the observed patterns and statistical analyses of the maximum temperature variability, we identified two types of heatwaves. The first-type of heatwave over the north-central India is found to be associated with blocking over the North Atlantic. The blocking over North Atlantic results in a cyclonic anomaly west of North Africa at upper levels. The stretching of vorticity generates a Rossby wave source of anomalous Rossby waves near the entrance of the African Jet. The resulting quasi-stationary Rossby wave-train along the Jet has a positive phase over Indian subcontinent causing anomalous sinking motion and thereby heatwave conditions over India. On the other hand, the second-type of heatwave over the coastal eastern India is found to be due to the anomalous Matsuno-Gill response to the anomalous cooling in the Pacific. The Matsuno-Gill response is such that it generates northwesterly anomalies over the landmass reducing the land-sea breeze, resulting in heatwaves.

Increasing heat waves and warm spells in India, observed from a multiaspect framework

“…Furthermore, Jenamani [] observed that the recurving of cyclonic storms strengthen low‐level westerly and thus prevent the onset of cooler sea breeze over coastal region, causing persistent heat waves. In contrast, the northcentral India heat waves are due to the anomalous quasi‐stationary wave originating at the entrance of the African Jet [ Ratnam et al ., ].…”

“…Moreover, the large‐scale climatic mode that modulate of the mean and extreme metrics of temperatures is the rising SST over Indian Ocean (SST‐IO) (heat waves generally occur during or succeeding El Niño events), which also induces less rainfall in India [ Panda et al ., ; Roxy et al ., ; Ratnam et al ., ; Rohini et al ., ]. Therefore, it is difficult to separate the influence of the significantly warming SST‐IO during 1951–2013 and 1981–2013 from that of the corresponding drying tendency (Figures d and f).…”

The Deadly Combination of Heat and Humidity in India and Pakistan in Summer 2015

“…Hospitals were overwhelmed with patients suffering from heat-related symptoms and at some point had to turn away patients (Salim et al 2015). It is difficult to be precise about the ultimate number of fatalities associated with these heat waves, but upwards of 2500 excess deaths are estimated to have occurred in the Indian heat wave (Ratnam et al 2016) and at least 700 alone in the Pakistani megacity of Karachi (Masood et al 2015) with many more throughout the country.…”

ENSO’s far reaching connection to Indian cold waves

“…The methodology followed for identifying the cold wave events is similar to that used by the authors for identifying heat wave events over India15. In this study, for identifying the cold wave events, we use the high resolution gridded temperature daily minimum temperature dataset of the India Meteorological Department (IMD)16.…”