Context: Canada broke a national heat record on June 27, when the temperature in a small town in British Columbia reached almost 116 degrees Fahrenheit. At least 134 people have died suddenly in Canada.

  • A historic heat wave is prevailing in the Pacific Northwest.
  • Heat waves are generally the result of trapped air. 

Causes behind heat waves: The heat wave was caused by what meteorologists described as a dome of high pressure over the Northwest and worsened by human-caused climate change

  • Heat domes: Heat domes or sprawling ridges of high pressure are a staple of summer. They bring copious sunshine and sinking air that heats up as it is compressed.
    • As the ground warms, it loses moisture, which makes it easier to heat even more. 
    • One should liken the Pacific ocean to a large swimming pool in which the heater is turned on. 
    • Once the heater is on, the portions of the pool close to the heating jets will warm up faster and therefore, the temperature in that area will be higher. 
    • In the same way, the western Pacific ocean’s temperatures have increased in the past few decades and are relatively more than the temperature in the eastern Pacific.
    • This strong change in ocean temperature from the west to the east is the reason for the heat dome, which is when the atmosphere traps heat at the surface, which encourages the formation of a heat wave. 
      • This is also the reason that the planet Venus is the hottest in the Solar System is because its thick, dense cloud cover traps the heat at the surface, leading to temperatures as high as 471 degree Celsius.

Heat Wave

  • A heat wave is a period of unusually hot weather that typically lasts two or more days. 
  • To be considered a heat wave, the temperatures have to be outside the historical averages for a given area. 
  • Heat waves begin when high pressure in the atmosphere moves in and pushes warm air towards the ground. 
  • That air warms up further as it is compressed and one begins to feel a lot hotter.
  • Criteria for heat wave in India: Heat wave is considered if maximum temperature of a station reaches at least 40 degree Celsius or more for Plains and at least 30 degree Celsius or more for Hilly regions.

What are favorable conditions for Heat wave?

  1. Transportation  /  Prevalence  of  hot  dry  air  over  a  region : There should be a region  of warm  dry  air  and  appropriate  flow  pattern  for  transporting  hot  air  over the region. 
  2. Absence  of  moisture  in  the  upper  atmosphere (As the presence of moisture restricts the temperature rise). 
  3. The  sky  should  be  practically  cloudless (To  allow  maximum  insulation  over the region).
  4. Large amplitude anti-cyclonic flow over the area: Heat waves generally develop over Northwest India and spread gradually eastwards &  southwards  but  not  westwards  (since  the  prevailing  winds  during  the  season  are westerly  to  northwesterly). 

Are heat waves dangerous for humans?

  • So as long as the body is producing sweat, which is then able to evaporate quickly, the body will be able to remain cool even under high temperatures. 
  • But there is a limit called the wet-bulb temperature–that considers heat and humidity–beyond which humans cannot tolerate high temperatures. 
  • Some heat-related illnesses include heat stroke, heat exhaustion, sunburn and heat rashes. 

Sources: https://www.hindustantimes.com/world-news/explained-what-s-causing-heat-wave-in-northwestern-us-canada-101625036778779.html