Ladakh experienced an unusually hot summer this year with temperatures soaring to 36 degree Celsius (96.8 degree Fahrenheit) in some parts of Leh district. The sun rays were so strong that it was difficult to step outside. The markets were empty during the afternoons as people chose to remain indoors. The merciless and fiery sun would drain anything that was exposed to it. It did not spare anything. Even the leaves of trees started to wilt and many of them were strewn along various roads.
My school friend from the plains was in Ladakh for a few days during which he signed up for a biking trip to explore different parts of the region. He had a great stay and promised to return again next year. It was from him that I first heard of the bizarre phenomenon of flights from Leh being cancelled due to high temperatures. His flight to Delhi was cancelled and he was forced to take a taxi to Srinagar and board a flight to Delhi.
Earlier, I had heard of flights being cancelled in the winter and spring, due to snowfall and reduced visibility. This made sense as Leh’s Kushok Bakula Rinpoche Airport requires a visual approach where the pilots rely on their vision—instead of using various navigational instruments—to land as well as take-off.
I started asking people about this odd phenomenon of flights to and from Leh being cancelled due to high temperatures. A Ladakhi friend mentioned that every summer, airlines that operate flights to and from Leh have to deal with the issue of heat as the airport is located at a high altitude—10,915ft (3,315m) above mean sea level (amsl). This means that these airlines do not accept cargo beyond a threshold to ensure that the aircraft does not exceed a certain weight. This is done to ensure that the aircraft can operate in the conditions prevalent in the context of the elevation and heat of Leh airport.
Even though airlines have been managing this issue all these years, most passengers have remained unaware of it. However, this precarious balancing act of temperature, altitude and aircraft got out of hand with 16 flight cancellations between 27 and 30 July, 2024 as temperatures around Leh airport soared to 36 degree Celsius (96.8 degree Fahrenheit) and above in the afternoons on those days.
Ladakh is a high altitude mountainous region. It is very challenging for pilots to manoeuvre an aircraft in such terrain even in the best conditions. It is not a surprise that only experienced pilots with years of special training and certification are deputed to operate on this sector. In addition to the terrain, pilots also have to contend with visibility in overcast conditions. Low visibility has led to a number of flight cancellations over the years, especially in the winter and spring. Furthermore, all flights in and out of Leh airport are operated from mid-morning (after 0600 hours) until mid-afternoon (1400 hours). The reason for this is that fierce wind patterns develop in this terrain later in the afternoon, which pose a serious hazard for aircrafts. High temperatures have now emerged as an additional challenge for civilian and military aircrafts in Ladakh, especially in the summer. In fact, this is the first time flight operations at Leh airport have been cancelled due to high temperatures—a clear indication of human-induced climate change. It took me some research to understand how high temperatures impacted aviation in Leh.
Based on my reading, the first thing we need to understand is the correlation between air density, temperature, and altitude. Scientists have developed a standard method to measure air density. This is called International Standard Atmosphere (ISA), which is density of air at a location at sea level at a temperature of 15 degree Celsius (59 degree Fahrenheit) and air pressure of 1,013 hectopascals. The temperature is then assumed to drop by 1.6 degree Celsius (35 degree Fahrenheit) for every 1,000 feet (305m) increase in elevation. Thus, the density of air i.e. the number of air molecules in a given unit of space, changes in relation to temperature and altitude. This means that air density can drop at sea level when temperatures increase. For instance, if the temperature at a location at sea level increases to 35 degree Celsius (95 degree Fahrenheit), it is called ISA+20 (as it is 20 degrees higher than the established standard) and the air density is equivalent to that experienced at an altitude of 2,400ft (732m) amsl even though the actual altitude has not changed. This is called density altitude and has important implications for aviation.
The second concept that we need to understand is how an aircraft functions. An aircraft gains height through the lift that is generated by its wings. Airplane wings are designed in such a manner that the upper portion of the wing is slightly curved in relation to the lower part, which is flat. When the aircraft is in motion, air travels faster over the upper portion of the wing and creates low pressure around the upper wing. Since air travels from high to low pressure, the pressure difference between the upper and lower sections of the wing generate lift, which allows an aircraft to gain height.
A similar concept is used in cricket to induce swing bowling. Fast bowlers shine one side of the ball and leave the other side rough. When the ball passes through the air, it starts to swing in the direction of the rough side where it encounters higher resistance to create low pressure. Thus, it is pressure difference that generates swing for fast bowlers. Similarly, bowlers also generate reverse swing once the ball is fairly old and one side is relatively more polished than the other. In such a condition, the ball behaves very differently and swings in the opposite side as compared to conventional swing. This is due to the pressure difference between the two hemispheres of the ball. In an old ball, both sides are rough but one side is slightly smoother. The airflow is such that it will first swing in the conventional way in the direction of the rough side but then changes its trajectory towards the end and swings in the opposite direction. That is because it experiences more turbulence as it travels through the air, which disrupts its flow and causes it to swing in the opposite direction.
Coming back to aircrafts, the amount of lift generated is determined by the air density and the speed at which the air passes over the wing. When the air density is lower due to higher temperatures, the aircraft has to increase its speed by using a longer runway. However, the thrust generated by the engines is also impacted by lower air density due to reduced air molecules available to it. Thus, the engineering design of aircrafts imposes a limit on the atmospheric conditions under which they can operate safely. As a corollary, pilots and airport staff determine the safety of aircraft operations by accounting for the altitude and temperature of the specific airport. Since, the altitude of an airport remains fixed, a standard temperature threshold is fixed above which aviation operations are deemed to be unsafe. In the case of Leh, the temperature threshold has been set at 32 degree Celsius (89 degree Fahrenheit) in the context of its altitude. The strategy of reducing the weight of the aircraft by limiting its cargo load offers no real benefits once the temperatures rise beyond the threshold.
This means that once the temperatures around Leh airport—given its altitude—rose beyond this threshold, the air became less dense with lower atmospheric pressure, and increased density altitude. This made air operations unsafe and led to the cancellations of flights. Aeronautics is a complex field, especially in relation to atmospheric conditions and high altitude conditions in mountainous regions such as Ladakh.
This highlights the seriousness of human-induced climate change and its impact on our lives. In addition to the inconveniences of flight cancellations, we are also experiencing droughts, floods, changing weather patterns, increased unpredictability, and shifts in ecosystems. This threatens all life-forms in mountainous regions such as ours, which have adapted to these challenging conditions over several millennia. Climate change is very real and it is rather scary. There is an urgent need for people around the world to unite and act to reverse and slow the process of global climate change before it is too late.
By Stanzin Kunkhen
Stanzin Kunkhen holds a Bachelor’s degree in psychology from Ambedkar University, Delhi.
