Air Pollution And Irrigation Mask The Extremes Of India’s 2019 Heatwave

Air Pollution And Irrigation Mask The Extremes Of India’s 2019 Heatwave

Farmer working on irrigation dykes, Uttar Pradesh, India. Credit: Purepix / Alamy Stock Photo

India is currently suffering one of the longest heatwaves in its recent history. Northern and central parts of the country have seen intense heat for more than 30 consecutive days, with temperatures in New Delhi topping 48C – the highest ever recorded in the capital in June.

Such an extended period of ferocious heat has been deadly. In the eastern state of Bihar, for example, 180 people have so far died, with hospitals “inundated with people suffering from heatstroke”.

The extreme weather follows in the footsteps of a lethal heatwave in 2016, when India recorded its highest-ever temperature of 51C in the western state of Rajasthan – one of the hottest temperatures ever recorded on earth.

Globally, the frequency and intensity of heatwaves are generally rising due to climate change. However, we do not yet see a clear upward trend in extreme temperatures in India.

A complex mix of competing human impacts means that, despite rising average temperatures, maximum temperatures have not risen in tandem. This article looks at the data, explains the (lack of a) trend and looks at the rising risks in store for the future.

Defining a heatwave

For India, May to June is typically the hottest period of the year, with temperatures often reaching up to 40C in the hottest areas before the cooling southwest monsoon rains arrive in July.

However, this year was worse than usual. As the map below shows, maximum temperatures reached well above 40C across most of India – and even into Pakistan.

Air Pollution And Irrigation Mask The Extremes Of India’s 2019 Heatwave

Map showing highest daily maximum temperature of the year 2019, based on data from ECMWF operational analyses and forecasts up to 27 June 2019. Red shading indicates the hottest temperatures, note that the colours start at 40C. Produced by Geert Jan Oldenborgh via the KNMI Climate Explorer.

Although it is easy to define and monitor when and where local record temperatures are broken, a heatwave is less straightforward as there are different metrics available.

Focusing on the one-day maximum temperature can be most relevant for rural outdoor workers, who are among the most vulnerable to heatwaves in India. A focus on longer durations, say three days, may better capture the impacts on urban populations and indoor workers. There are also heatwave indices that account for factors beyond temperature, notably humidity, which is known to play an important role in how heat impacts the human body.

Nevertheless, in a warming climate we expect heat records to be broken more frequently and for heatwaves to become more intense. We see this in many parts of the world, with rising intensity and frequency of heatwaves attributed to human-caused climate change.

This includes the famous 2003 heatwave in Europe, responsible for more than 70,000 deaths, which was the first event where scientists were able to identify a human influence. The likelihood of this event had more than doubled due to climate change. (It has continued to increase since then.)

While it might be expected that the dominant impact of global warming would extend to India, there are a number of other important factors that affect maximum temperatures locally.

Worsening air pollution blocks more and more sunlight and, thus, decreases maximum temperatures. In addition, increasing irrigation means that more of the heat is used to evaporate water and less to warm the air.

Finally, while in many big cities the “urban heat island” effect leads to hotter heat waves, some cities in the dry north of India actually show an “urban cool island” effect driven by higher water usage compared to the surrounding arid land areas.

Taken together, these factors play as large a role as global warming and counteract the expected upward trend in heatwaves – at least for now.

Competing impacts

To investigate how all these factors affect heatwaves we need reliable observations. For India, these are not easy to obtain.

Publicly accessible global datasets often have large amounts of missing data over India. Worse, the amount of missing data in the 1970s was so high that many heatwaves were likely not recorded in those years. This leads to an artificial upward trend after the 1970s as the number and quality of weather measurements improved.

An alternative option is to use temperature records based on a combination of direct measurements and a weather model – an approach known as “reanalysis”. While these are not perfect, they are presently the best publicly available basis to study real-world occurrences of heatwaves.

Analysing both the observations (corrected for missing data) and reanalyses, we find no trend in the highest maximum temperatures of the year over most of India since the 1970s. This holds for heatwave definitions from single hot days to weekly averages and even for the monthly average of maximum temperatures in May and June.

The chart below shows the highest daily maximum temperature of the year, as an average over India, over the past 40 years (red line). The green line shows a slightly declining trend over that time.

Overall, maximum temperatures in the hottest months do not tend to show an increasing trend across India. Instead, the high temperatures of 2019 seem due to the natural year-to-year variability of the weather.

Air Pollution And Irrigation Mask The Extremes Of India’s 2019 Heatwave

Average over India of the highest daily maximum temperature of the year (ERA-interim extended with operational analyses and forecasts up to 30 June 2019). Produced by Geert Jan Oldenborgh.

Our analysis suggests that the combination of increased air pollution and irrigation have more or less offset the warming from increased greenhouse gases.

So, how do we know this?

Well, while maximum temperatures have not increased, minimum temperatures have. As daily minimum temperatures typically occur at night, they are much less affected by air pollution (which primarily affects incoming solar radiation).

And, indeed, we see that the hottest nights of the year have increased since the 1970s over large parts of India. This means that, overall, average temperatures have continued to rise. The chart below shows the highest daily average temperatures averaged over India for the past 40 years (red line). The green line shows a small increasing trend.

Air Pollution And Irrigation Mask The Extremes Of India’s 2019 Heatwave

Average over India of the highest daily average temperature of the year (ERA-interim extended with operational analyses and forecasts up to 27 June 2019). Produced by Geert Jan Oldenborgh via the KNMI Climate Explorer.

In addition, relative humidity in May has increased strongly since the 1970s, probably due in part to irrigation. Therefore, despite the fact that there is no clear increase in maximum temperature extremes, heat indices that take humidity into account do show upward trends: heatwaves have become more humid, posing greater risk to human health. Increased air pollution also substantially increases the negative health impacts of heatwaves, but as far as we know this has not yet been quantified.

The conclusion is that the meteorological heatwaves described by the highest one-day – and multiple-day – maximum temperature trends have not increased in intensity over India since the 1970s, contrary to most of the rest of the world.

And, so, while the current heat in 2019 is more severe than in the last few years, this is not yet part of a clear systematic trend. But health impacts of heatwaves have been getting more severe due to higher humidity and more air pollution.

Expected trends

For the future, we expect that a clear signal of human-caused climate change to emerge in maximum temperatures as measures are put in place in India to improve air quality.

A similar effect was seen in western Europe where summers only became hotter from the mid-1980s onwards when emission of pollutants was successfully regulated and reduced.

In addition, with expanding groundwater depletion, keeping up the present-day irrigation rates could prove challenging for parts of India. Thus, both factors currently counteracting the impacts of global warming on Indian heat extremes are likely to change.

Given that greenhouse gas concentrations continue to increase, we expect to see an amplified upward trend in heatwaves in the not too distant future.

It is important to note that climate models typically do not include the effects of irrigation and are sometimes limited in how they represent air pollution. More research – including better model representation of these factors – is, therefore, needed to better quantify the different drivers of heat extremes and more reliably assess future heatwave risks.

Adaptation

The impacts of heatwaves also strongly depend on vulnerability and exposure of people and the systems they rely on.

On the one hand, these factors can also contribute to the rising risk of heatwaves, but they may also offer opportunities to better manage those risks, even in the face of increasing heat.

The extent to which people have to work outside and the availability of clean water – and sometimes even air-conditioning – can make an immense difference for reducing heat deaths and hospital admissions.

Advice to vulnerable groups on behaviour during periods of heat – such as drinking enough water – and sometimes even government regulation – for instance, prohibiting outside labour during the hottest hours – can also have an enormous impact. Over the longer run, urban design, including housing but also urban green space, also needs to take more account of rising heat risks.

In France, the “Plan Canicule” initiated after the deadly 2003 heatwave has very significantly reduced excess deaths in similar heatwaves, In India, the “Heat Action Plan” implemented in the city of Ahmedabad have been shown to have drastically reduced mortality during the heatwave of 2015. Yet many cities do not yet have such plans and many countries don’t even have heatwave early warnings, despite excellent predictability and the rising risks.

In the long-term, the projected increases in heat and humidity will require much more efforts to better manage the rising risk of heatwaves. If global warming continues unabated, it could challenge the ability for humans, livestock and wildlife to survive outdoors in parts of India.

This article originally appeared on CarbonBrief

About The Author

Dr Geert Jan van Oldenborgh, Dr Gabriel Vecchi, Dr Flavio Lehner, Dr Friederike Otto, Dr Karsten Haustein, Dr Claudia Tebaldi, Dr Maarten van Aalst and Dr Krishna AchutaRao are from the World Weather Attribution collaboration.

Related Books

Climate Change: What Everyone Needs to Know

by Joseph Romm
0190866101The essential primer on what will be the defining issue of our time, Climate Change: What Everyone Needs to Know® is a clear-eyed overview of the science, conflicts, and implications of our warming planet. From Joseph Romm, Chief Science Advisor for National Geographic's Years of Living Dangerously series and one of Rolling Stone's "100 people who are changing America," Climate Change offers user-friendly, scientifically rigorous answers to the most difficult (and commonly politicized) questions surrounding what climatologist Lonnie Thompson has deemed "a clear and present danger to civilization.". Available On Amazon

Climate Change: The Science of Global Warming and Our Energy Future second edition Edition

by Jason Smerdon
0231172834This second edition of Climate Change is an accessible and comprehensive guide to the science behind global warming. Exquisitely illustrated, the text is geared toward students at a variety of levels. Edmond A. Mathez and Jason E. Smerdon provide a broad, informative introduction to the science that underlies our understanding of the climate system and the effects of human activity on the warming of our planet.Mathez and Smerdon describe the roles that the atmosphere and ocean play in our climate, introduce the concept of radiation balance, and explain climate changes that occurred in the past. They also detail the human activities that influence the climate, such as greenhouse gas and aerosol emissions and deforestation, as well as the effects of natural phenomena.  Available On Amazon

The Science of Climate Change: A Hands-On Course

by Blair Lee, Alina Bachmann
194747300XThe Science of Climate Change: A Hands-On Course uses text and eighteen hands-on activities to explain and teach the science of global warming and climate change, how humans are responsible, and what can be done to slow or stop the rate of global warming and climate change. This book is a complete, comprehensive guide to an essential environmental topic. Subjects covered in this book include: how molecules transfer energy from the sun to warm the atmosphere, greenhouse gases, the greenhouse effect, global warming, the Industrial Revolution, the combustion reaction, feedback loops, the relationship between weather and climate, climate change, carbon sinks, extinction, carbon footprint, recycling, and alternative energy. Available On Amazon

From The Publisher:
Purchases on Amazon go to defray the cost of bringing you InnerSelf.comelf.com, MightyNatural.com, and ClimateImpactNews.com at no cost and without advertisers that track your browsing habits. Even if you click on a link but don't buy these selected products, anything else you buy in that same visit on Amazon pays us a small commission. There is no additional cost to you, so please contribute to the effort. You can also use this link to use to Amazon at any time so you can help support our efforts.

 

 

enafarzh-CNzh-TWdanltlfifrdeiwhihuiditjakomsnofaplptruesswsvthtrukurvi

follow InnerSelf on

facebook-icontwitter-iconrss-icon

 Get The Latest By Email

{emailcloak=off}

EVIDENCE

PBS Nova's Polar Extremes
PBS Nova's Polar Extremes
by PBS
In this two-hour special, renowned paleontologist Kirk Johnson takes us on an epic adventure through time at the polar…
Climate Research Struggles To Find Funding
Climate Research Struggles To Find Funding
by Kieran Cooke
Climate research is the poor relation of the academic world. Since 1990 it’s won less than 5% of the research funds…
Atlantic Current Could Falter Before 2100
Atlantic Current Could Falter Before 2100
by Tim Radford
v The Atlantic current won’t come to a full stop the day after tomorrow. But it could face a temporary halt later this…
Temperature in Antarctica Soars Past 69°F as NOAA Reports Last Month Was World's Hottest January on Record
Temperature in Antarctica Soars Past 69°F as NOAA Reports Last Month Was World's Hottest January on Record
by Jessica Corbett
While the reading in Antarctica still needs to be confirmed, the Brazilian scientists who logged it called the new…
CO₂ Levels And Climate Change: Is There Really A Controversy?
CO₂ Levels And Climate Change: Is There Really A Controversy?
by Guillaume Paris and Pierre-Henri Blard
The relationship between atmospheric CO2 levels and climate change is often perceived as a controversial subject.
Ancient Antarctic Ice Melt Caused Extreme Sea Level Rise 129,000 Years Ago – And It Could Happen Again
Ancient Antarctic Ice Melt Caused Extreme Sea Level Rise 129,000 Years Ago – And It Could Happen Again
by Chris Fogwill, et al
Our new research might be able to provide some insight into what effect a warmer world would have in Antarctica, by…
3 Things Historical Literature Can Teach Us About The Climate Crisis
3 Things Historical Literature Can Teach Us About The Climate Crisis
by David Higgins and Tess Somervell
New novels about climate change – climate fiction, or cli-fi – are being published all the time. The nature of the…
Antarctica Has Lost Nearly 3 Trillion Tonnes Of Ice Since 1992
Antarctica Has Lost Nearly 3 Trillion Tonnes Of Ice Since 1992
by Thomas Slater and Andrew Shepherd
It can be easy to overlook the monstrous scale of the Antarctic ice sheet. Ice, thick enough in many places to bury…

LATEST VIDEOS

PBS Nova's Polar Extremes
PBS Nova's Polar Extremes
by PBS
In this two-hour special, renowned paleontologist Kirk Johnson takes us on an epic adventure through time at the polar…
A huge iceberg just broke off West Antarctica’s most endangered glacier
A Huge Iceberg Just Broke Off West Antarctica’s Most Endangered Glacier
by Madeleine Stone
Huge blocks of ice regularly shear away from Antarctica’s ice shelves, but the losses are speeding up.
The Rise Of Solar Power
by CNBC
Solar power is on the rise. You can see the evidence on rooftops and in the desert, where utility-scale solar plants…
World's Largest Batteries: Pumped Storage
by Practical Engineering
The vast majority of our grid-scale storage of electricity uses this clever method.
Hydrogen Fuels Rockets, But What About Power For Daily Life?
Hydrogen Fuels Rockets, But What About Power For Daily Life?
by Zhenguo Huang
Have you ever watched a space shuttle launch? The fuel used to thrust these enormous structures away from Earth’s…
Fossil Fuel Production Plans Could Push Earth off a Climate Cliff
by The Real News Network
The United Nations is beginning its climate summit in Madrid.
Big Rail Spends More on Denying Climate Change than Big Oil
by The Real News Network
A new study concludes that rail is the industry that's injected the most money into climate change denial propaganda…
Did Scientists Get Climate Change Wrong?
by Sabine Hossenfelder
Interview with Prof Tim Palmer from the University of Oxford.

LATEST ARTICLES

Stories Of When Your Kids Make You Feel Old! | The Curls
Old Conservative White Men: Pass The Football To Someone Who Will Try To Score
by Robert Jennings, InnerSelf.com
We have had important US elections but this one in November 2020 is undoubtedly the most important. Why? America and…
How Tiny Microbes Are Revolutionizing Big Agriculture
How Tiny Microbes Are Revolutionizing Big Agriculture
by Mathew Wallenstein, Colorado State University
Walk into your typical U.S. or U.K. grocery store and feast your eyes on an amazing bounty of fresh and processed…
Uk’s Nuclear Future Hangs On Electricity Tax
Uk’s Nuclear Future Hangs On Electricity Tax
by Paul Brown
The new British prime minister, Boris Johnson, must soon decide whether to save the UK’s nuclear future with an…
Extreme Weather Could Push The U.S. Into Recession
Extreme Weather Could Push The U.S. Into Recession
by Karen Nikos
Physical climate risk from extreme weather events remains unaccounted for in financial markets, a new paper warns.
Why West Coast Water Troubles Will Head East
Why West Coast Water Troubles Will Head East
by Daniel Stolte
Even under modest climate change scenarios, the continental United States faces a significant loss of groundwater, a…
Ecuador's Fuel Protests Show The Risks Of Removing Fossil Fuel Subsidies Too Fast
Ecuador's Fuel Protests Show The Risks Of Removing Fossil Fuel Subsidies Too Fast
by Katherine Monahan
The protests started on Oct. 2 in response to the federal government’s “Decreto 883,” a packet of economic adjustments…
Natural Flood Management Would Be Overwhelmed By Britain's Winter Super-floods
Natural Flood Management Would Be Overwhelmed By Britain's Winter Super-floods
by Robert Wilby and Simon Dadson
As large swathes of the UK endure the worst floods in living memory, hearts and minds are rightly focused on protecting…
Keeping The City Cool Isn't Just About Tree Cover – It Calls For A Commons-based Climate Response
Keeping The City Cool Isn't Just About Tree Cover – It Calls For A Commons-based Climate Response
by Abby Mellick Lopes and Cameron Tonkinwise
A recent report by the Greater Sydney Commission singles out urban heat as one of four priority areas given our coming…