Heat and Cold Waves Over India
D.S. Pai, A.K. Srivastava and Smitha Anil Nair
During the period 1901-2012, almost the entire globe has warmed with a rise of about
0.84 °C in the annual surface air temperature averaged over the globe (land + ocean) leading to significant changes in the frequency and intensity of extreme weather and climate events, such as heat waves (HWs) and cold waves (CWs), droughts and floods, hurricanes, tornadoes and thunderstorms, over various parts of the world (IPCC 2013). Changes in the extreme weather and climate events pose significant threats on our environment as well as on the life, health and well-being of the human society (Easterling et al. 2000; Meehl and Tebaldi 2004; Balbus and Malina 2009; Coumou and Rahmstorf 2012). The HWs and CWs are one of the less-known forms of extreme weather as they are not visible as other forms of severe weather. However, these abnormal temperature events can impose severe physiological stress on the human body as the body operates best within a fairly normal temperature range. There is a marked relationship between human mortality and thermal stress. During unusually cold/hot episodes, deaths from different causes can rise significantly with the elderly at greater risk than others (WMO 1996). In USA, 3829 of the 8015 heat-related deaths recorded during the period 1979-1999 were attributed to weather conditions (Donoghue et al. 2003). In 2003, Europe witnessed the hottest summer on record since 1540, which had huge adverse impacts (Garcia-Herrera et al. 2010).
In India, manifold increase in the human deaths was observed during various heat waves (HWs) of 1995, 1998 and 1999 (De 2001). Similarly, an intense cold wave over North India during the first to third week of January 2003 caused deaths of more than 900 people of which 813 were from Uttar Pradesh (De et al. 2005). Figure 1 shows the deaths caused by HWs and CWs during the period 1971-2010. In Fig. 1, time series of deaths due to both HWs and CWs does not show any
© Springer Science+Business Media Singapore 2017 51
M.N. Rajeevan and S. Nayak (eds.), Observed Climate Variability and Change Over the Indian Region, Springer Geology, DOI 10.1007/978-981-10-2531-0_4
Fig. 1 Number of deaths in India annually due to HW/CWs for the period 1971-2010 obtained from media reports and IMD’s annual disaster weather reports. The red (blue) bars corresponds to deaths due to HW/SHWs (CW/SCWs) (color figure online)
noticeable trends. However, number of deaths due to heat wave events was the highest during the recent decade (2001-2010) compared to the previous three decades.
The heat (cold) waves represent rise (fall) of maximum (minimum) temperature at a given place by a certain amount from its climatological value. In India, the HWs are generally observed during March to July, and CWs are observed during November to March with each of these extreme events mostly experienced during the middle 3-month period of the respective seasons; hot weather season of April- June (AMJ) and cold weather season of December to February (DJF), respectively. Due to significant impact of HWs and CWs on the human health and observed changes in their frequency, intensity and persistency over various parts of the globe, there have been many studies on these extreme temperature events over India and their impact on human mortality (Raghavan 1966, 1967; Rai Sircar and Datar 1963; Natarajan 1964; Bedi and Parthasarathy 1967; Bedekar et al. 1974; Subbaramayya and Surya Rao 1976; Chaudhury et al. 2000; De 2001; De et al. 2005; Pai et al. 2004, 2013). However, each of these studies used different threshold temperature values to describe the HWs and CWs.
Here, we describe various characteristics such as frequency, persistency and spatial coverage of HWs and CWs in the country during the seasons of AMJ and DJF, respectively, and the associated decadal variations. In addition, trends in the frequencies of these extreme temperature events and changes associated with the two ENSO phases (El Nino and La Nina) have been also highlighted.