A sixfold rise in concurrent day and night-time heatwaves in India under 2 °C warming

Abstract

Heatwaves with severe impacts have increased and projected to become more frequent under warming climate in India. Concurrent day and nighttime heatwaves can exacerbate human discomfort causing high morbidity and mortality; however, their changes in the observed and projected climate remain unrecognized. Here using observations and model simulations from climate of 20th century plus (C20C+) detection and attribution (D&A) and coupled model intercomparison project 5 (CMIP5) projects, we show that 1 and 3-day concurrent hot day and hot night (CHDHN) events have significantly increased during the observed climate in India. Our results show that the anthropogenic emissions contribute considerably to the increase of 1 and 3-day CHDHN events in India. The frequency of 3-day CHDHN events is projected to increase 12-fold of the current level by the end of 21st century and 4-fold by the mid 21st century under the high emission pathway of RCP 8.5. The increase in 3-day CHDHN events can be limited to only 2-fold by the end of 21st century under low emission scenario of RCP 2.6. One and 3-day CHDHN events are projected to increase by 4, 6, and 8 folds of the current level in India under the 1.5, 2, and 3 °C warming worlds, respectively. Restricting global mean temperature below 1.5° from the pre-industrial level can substantially reduce the risk of 1 and 3-day CHDHN events and associated implications in India.

Half‐a‐Degree Matters for Reducing and Delaying Global Land Exposure to Combined Daytime‐Nighttime Hot Extremes

“…However, this univariate definitional framework, on the one hand, may introduce potential entanglements among types of hot extremes (Oswald & Rood, 2014;Oswald, 2018) and, on the other hand, tends to underestimate impacts exacerbated by coincident/interacted drivers (Fischer & Schär, 2010;Zscheischler et al, 2018). Instead, a bivariate definitional framework, with the extremity of both daytime and nighttime temperatures constrained, is warranted to achieve a genuine nonoverlapping classification consisting of daytime-only, nighttime-only, and combined daytime-nighttime hot extremes (hereafter called combined hot extremes; Chen & Zhai, 2017;Gershunov et al, 2009;Mukherjee & Mishra, 2018;Oswald & Rood, 2014). A case in point is that a univariate constraint for hot days (daily maxima ≥90th percentile), which is intended for extreme daytime temperature only, may lead to an unintended identification of nighttime hot extremes as well, since the constraint fails to eliminate the possibility of threshold-exceeding nighttime minima.…”

“…A case in point is that a univariate constraint for hot days (daily maxima ≥90th percentile), which is intended for extreme daytime temperature only, may lead to an unintended identification of nighttime hot extremes as well, since the constraint fails to eliminate the possibility of threshold-exceeding nighttime minima. Instead, a bivariate definitional framework, with the extremity of both daytime and nighttime temperatures constrained, is warranted to achieve a genuine nonoverlapping classification consisting of daytime-only, nighttime-only, and combined daytime-nighttime hot extremes (hereafter called combined hot extremes; Chen & Zhai, 2017;Gershunov et al, 2009;Mukherjee & Mishra, 2018;Oswald & Rood, 2014). These distinct types actually arise from differing thermodynamic-dynamic drivers (Barbier et al, 2018;Cowan et al, 2017;Freychet et al, 2017;Ma et al, 2015), show type-specific responses to global warming Fischer & Schär, 2010), and hold varying levels of impact relevance to various sectors (Gosling et al, 2009;Karl & Knight, 1997;Nairn & Fawcett, 2013;Robinson, 2001).…”

Anthropogenically-driven increases in the risks of summertime compound hot extremes

“…In a warming climate, increasingly frequent and intense hot extremes have been reported globally with strong evidence pointing to a large contribution from anthropogenic warming [5][6][7][8] . Severe damage comes from sequential occurrences of hot day and hot night within 24 h, which accumulate and aggravate adverse impacts of daytime and nighttime heat on various sectors 9,10 . Some studies considered both diurnal and nocturnal temperatures, for instance using daily mean temperature as a measurement 11,12 .…”

Assessing Changes in Characteristics of Hot Extremes Over India in a Warming Environment and their Driving Mechanisms

“…Long observational records reveal a significant increasing trend in the mean (0.48 °C), minimum (0.22 °C), and maximum (0.74 °C) temperatures over India during 1901India during -2003 18 . In recent decades, India has been considerably affected by hot extremes that killed more than thousands of people in the years 1998, 2010, 2013, and 2015 [20][21][22] . The station data over India shows an increasing trend in the frequency of hot days (especially over the eastern and western coasts as well as over the interior peninsula) 23 and a widespread increase in the intensity of those events (i.e., out of 121 stations considered, 70% of stations illustrate an increasing trend) during the last three decades of the 20 th century 24 .…”