US Heat Wave

US Heat Wave

Subject: Geography

Context : One of the hottest cities on the continent on Monday was Salem, Oregon, about 45 miles southwest of Portland, where the high temperature reached 117 degrees Fahrenheit in the afternoon, a record for the city.

Concept :

• In most parts of the country, temperatures must be above the historical average in an area for two or more days before the label “heat wave” is applied to a hot spell, according to the National Weather Service

Why is it hotter than normal in North America?

• We have long known that the world has warmed by more than 1 degree Celsius (about 1.8 degrees Fahrenheit) since 1900, and that the pace of warming has accelerated in recent decades. The warmer baseline contributes to extreme-weather events and helps make periods of extreme heat more frequent, longer and more intense.

Heat Wave

• A heat wave is a period of abnormally high temperatures, more than the normal maximum temperature that occurs during the summer season in the North-Western and South Central parts of India.
• Heat waves typically occur between March and June, and in some rare cases even extend till July.
• Higher daily peak temperatures and longer, more intense heat waves are becoming increasingly frequent globally due to climate change.

Criteria for Heat Waves in India

• The heat wave is considered when the maximum temperature of a station reaches at least 40°C for Plains and at least 30°C for Hilly regions.
• If the normal maximum temperature of a station is less than or equal to 40°C, then an increase of 5°C to 6°C from the normal temperature is considered to be heat wave condition.
• Further, an increase of 7°C or more from the normal temperature is considered as severe heat wave condition.
• If the normal maximum temperature of a station is more than 40°C, then an increase of 4°C to 5°C from the normal temperature is considered to be heat wave condition. Further, an increase of 6°C or more is considered as severe heat wave condition.
• Additionally, if the actual maximum temperature remains 45°C or more irrespective of normal maximum temperature, a heat wave is declared.

Heat Domes

• High-pressure circulation traps hot ocean air like a lid or a cap trapping heat at the surface and favouring the formation of a heat wave.
• Higher daily peak temperatures and longer, more intense heat waves are becoming increasingly frequent globally due to climate change