Average Number of Heat Wave Days refers to the average count of days in a year or season when a region experiences heat wave conditions, based on long-term historical climate data. A heat wave is typically declared when the maximum temperature rises significantly above normal—usually 4.5°C to 6.4°C or more above the average—or when the temperature exceeds 45°C (or 40°C in coastal areas) for at least two consecutive days, as defined by the India Meteorological Department (IMD).

The average number of heat wave days is a crucial metric in understanding climate variability and change, especially in the context of global warming. Rising trends in this indicator signal increased exposure to extreme temperatures, which can severely impact public health, agriculture, water resources, and energy consumption. Prolonged heat waves increase the risk of heat strokes, dehydration, and cardiovascular stress, particularly among vulnerable groups like the elderly, outdoor workers, and low-income populations. In agriculture, heat waves can cause crop failure, reduce yields, and affect livestock. Monitoring this average helps in formulating climate adaptation strategies, improving early warning systems, and guiding urban planning (e.g., designing heat-resilient infrastructure). It also supports national and regional efforts in building climate-resilient communities and ensuring sustainable development under increasing temperature extremes.