A heat wave occurs throughout the summer when the maximum temperature significantly exceeds its normal range. Over the northwest regions of the country, the increasing maximum temperature that began during the pre-monsoon months frequently lasts until June, in rare instances into July.

Cold waves are occurrences of extremely low temperatures that are brought on by dry, cold winds from the north entering the subcontinent. Transient disturbances in the mid-latitude westerlies, which frequently exhibit mild frontal characteristics, have an impact on the northern sections of India, particularly the mountainous regions and adjacent plains. 

Heatwave and Coldwave:

• There are typically five to six heatwave events per year over northern parts of India between March and June, and they can even extend into July in some cases. Single events can last weeks, occur consecutively, and can impact a large population. Bihar, Jharkhand, West Bengal (Gangetic), Odisha, Punjab, Haryana, Chandigarh, Delhi, Rajasthan, Maharashtra, and West Madhya Pradesh were affected by severe heatwaves in 2016.
• Snowfall in high altitude areas such as north of Delhi, including places in Jammu and Kashmir, Himachal Pradesh, and Uttarakhand is a significant cause of Cold waves. These regions blow cold winds that lower temperatures acrossnorthwest India, including Delhi, every winter.
• In India, the number of deaths per year associated with abnormally cold temperatures is 6,55,400, while the number of deaths associated with high temperatures is 83,700, according to the research done by the Lancet study.

Cold waves have caused a lot of deaths and suffering recently in India due to the worsening of the air quality in metropolitan areas. Due to their low levels of development and lack of shelter options for farmers and outdoor labourers, UP and Bihar have the highest cold wave casualty rates. 

Casualties brought on by heat waves have slightly increased recently. Urbanization is a new factor that contributes to human death and suffering by reducing the Diurnal Temperature Range (DTR).