A heatwave that's too hot for India to handle, with more to come

India is currently in the throes of yet another extreme heat event, with the death toll rising past 1,100. The current heatwave began on May 21, and is forecast to continue until May 30, with temperatures in many regions exceeding 45C, and reaching 47.6C and beyond.

Delhi has now endured seven consecutive days over 44C, the worst extreme heat event recorded in a decade, according to the India Meteorological Department.

Even in the mountain town of Mussoorie close to Nepal, 2,010 m above sea level, temperatures rose to 36C.

Residents of the Indian subcontinent might be acclimatised to heat and humidity, but they too have their heat tolerance limits. So what can this tell us about the future?

What happens in a heatwave?

Despite health warnings of high chances of heatstroke, dehydration and fatality, more than 1,100 deaths have been recorded (as of May 27). However these figures are expected to escalate. Construction workers, the elderly and young are vulnerable. Taxi drivers stopped work between 11am and 4pm in Kolkata after two died from heat stroke.

The southern regions of Andhra Pradesh and Telangana have been most severely affected. Yet these regions are accustomed to high summer temperatures peaking at 45C, but this hot spell is exceeding even their high heat tolerance.

Heat at this level is inescapable. People die in their homes, at work, even in hospitals. The human thermoregulatory system has limits. Our muscles generate heat, which must be shed to the environment to maintain our core temperature of about 36.7C. Evaporation of sweat helps us keep cool when it is hot, but we can only sweat a few litres per hour, which makes us dehydrated. And when this is not enough to drive sufficient heat loss, our core temperature rises to dangerous levels (my paper on this is under review, not yet in print).

Acclimatisation to heat can only offer limited protection. Avoiding the sun and physical exertion, maintaining hydration, and resting in a cool place are critical to survival in these conditions.

However, serious challenges arise when extreme heat events linger for prolonged periods, as cessation of activities for weeks is often not an option. Societal life cannot grind to a stop. Yet persevering in the heat can be lethal.

Relief for India is not anticipated until the Indian Ocean monsoon makes landfall in the southern state of Kerala on May 30 or 31, and it will take weeks before it reaches the northern half of the country, where intense heat and dry winds have caused severe dehydration on a mass scale.

The number of people affected by this event is staggering. India is home to nearly 1.3 billion souls, one sixth of the world’s population. Every year, India adds more people than any other nation in the world, and some of its individual states are as populous as large nations like Brazil.

In Delhi, India’s second-biggest city, home to nearly 10 million people, electric power has been cut off multiple times as many households run their air-conditioners to their maximum for several hours during the day. Without power, food spoils. Street food vendors also struggle to prevent spoiling of food, even when recently prepared. Outbreaks of food poisoning spike after heat events, and water security is also a challenge.

Is it climate change?

While we will have to wait for analysis of this heatwave, others have calculated how climate change has affected the likelihood of extreme heat.

Attribution analyses can now detect the climate change finger print. We can now calculate the increased likelihood that specific extreme events are due to anthropogenic forcings, that is, our continually escalating rate of greenhouse gas emissions.

Human influence at least doubled the chances of recent UK events according to the first formal event attribution study, which also made the ominous forecast that severe heatwaves could become commonplace by the 2040s. Sophie Lewis and David Karoly calculated that there was at least a 2.5 times increase in the odds that Australian extreme heat events are due to human influences to 2005, and a fivefold increase in this risk using simulations for 2006–2020.

On average, India as warmed 0.60C during last 112 years, with Goa and Tamil Nadu in southern India recording the highest increase in monthly mean maximum temperature (0.05C per year) and (0.04C per year) respectively.

Heavy rainfall events are increasing in frequency and low and medium rainfall events are decreasing. This current heat wave was most intense across the southern regions of Andhra Pradesh and Telangana where projected temperature increases by 2100 are lower, compared to the north where changes of up to 4.5C are projected.

The economic costs

Food crops are also highly sensitive to heat. Globally, more than 220 million hectares are annually sown to wheat, making it the most widely grown crop in the world, and a vital global food source. Preferring relatively cool temperatures, wheat is harvested before early summer. Temperatures above 30C shorten grain-filling duration, interrupt photosynthesis and then slows or stops grain-filling rates. Yields are reduced and nutritional quality is degraded.

Extreme heat exposure, such as the current heat wave will undoubtedly lead to crop losses in India. Two of India’s major crops (wheat and rice) are projected to decline with continued global warming. The economic value of these losses could reach $US208b by 2050 and US$366b by 2100 (all prices are in 2010 US$).

In a country where the agriculture sector provides a livelihood source for more than 65% of the population the ramifications of this heat event will be widely felt. Annual incomes lost, food price rises, increases in hunger and malnutrition, which further lowers resilience and increases population susceptibility to disease, and can easily ignite or exacerbate poverty cycles.

In response to the 2010 heatwave and fires around Moscow, Russia ceased grain exports following the massive reduction in yield, and to protect national food security. Global food prices soared. This is becoming a regular phenomenon. Over recent years, heat and drought events have slashed yields in Australia, the US, and Argentina.

The Indian government’s aim is to be self-sufficient in terms of food production. Given these realities, any decline in agriculture production is bound to be costly for the nation.

Climate change can affect well-being in poor economies more than previously shown if its effect on economic growth, and not only on current production, as well as health and wellbeing, and capacity to contribute to society are also considered.

The combination of rapidly expanding population, and increasing extreme heat events reducing food yields suggests a perfect storm is brewing.

We can stop this if we want to by mitigating and adapting to climate change. But we must want to. Waiting for someone else do make a difference is condemning us all to a future where these events are commonplace.

Liz Hanna receives funding from an NHMRC grant to research impacts of heat on human population, specifically workers, and has previously received other NHMRC project grants to identify health impacts, acclimatisation limits and adaptive options. She is President of the Climate and Health Alliance and Fellow at the Research School of Population Health, National Centre for Epidemiology & Population Health at ANU