have periodically led to major Indian famines. These include the Bengal famine of 1770, in which up to one third of the population in affected areas died; the 1876–1877 famine, in which over five million people died; the 1899 famine, in which over 4.5 million died; and the Bengal famine of 1943, in which over five million died from starvation and famine-related illnesses. All such episodes of severe drought correlate with El Niño-Southern Oscillation (ENSO) events. El Niño-related droughts have also been implicated in periodic declines in Indian agricultural output. Nevertheless, ENSO events that have coincided with abnormally high sea surfaces temperatures in the Indian Ocean—in one instance during 1997 and 1998 by up to —have resulted in increased oceanic evaporation, resulting in unusually wet weather across India. Such anomalies have occurred during a sustained warm spell that began in the 1990s. A contrasting phenomenon is that, instead of the usual high pressure air mass over the southern Indian Ocean, an ENSO-related oceanic low pressure convergence centre forms; it then continually pulls dry air from Central Asia, desiccating India during what should have been the humid summer monsoon season. This reversed air flow causes India's droughts. The extent that an ENSO event raises sea surface temperatures in the central Pacific Ocean influences the extent of drought. Heat waves A study from 2005 concluded that heat waves significantly increased in frequency, persistence and spatial coverage in the decade 1991–2000, when compared to the period between 1971–80 and 1981–90. A severe heat wave in Orissa in 1998 resulted in nearly 1300 deaths. Based on observations, heat wave related mortality has increased in India prior to 2005. The 2015 Indian heat wave killed more than 2,500 people. Extremes Extreme temperatures: low India's lowest recorded temperature was in Dras, Ladakh. However, temperatures on Siachen Glacier near Bilafond La () and Sia La () have fallen below , while blizzards bring wind speeds in excess of , or hurricane-force winds ranking at 12—the maximum—on the Beaufort scale. These conditions, not hostile actions, caused more than 97% of the roughly 15,000 casualties suffered among Indian and Pakistani soldiers during the Siachen conflict. Extreme temperatures: high The highest temperature ever recorded in India occurred on 19 May 2016 in Phalodi, Jodhpur District, Rajasthan at . Before this, the highest reliable temperature reading was in Alwar, Rajasthan in 1955. The India Meteorological Department doubts the validity of readings