Draft:District Wise Heat Threshold for Heat Wave Alert in India

The District Wise Heat Threshold for Heat Wave Alert has been developed by the Uttar Pradesh State Disaster Management Authority (UPSDMA) Government of Uttar Pradesh for pan India. The draft report entitled "District Wise Heat Threshold Determination for Uttar Pradesh and India-2024" addresses the escalating challenge of increasing heat wave frequency and intensity while defining Heat Threshold for each districts. The report delineates thresholds for Yellow, Orange and Red alerts, aiming to empower decision-makers with targeted intervention strategies. By integrating these thresholds into disaster risk reduction strategies, the report promotes proactive heat wave management, prioritising the protection of vulnerable populations, the preservation of livelihoods and sustainable community development, thereby fostering a culture of resilience and adaptive governance for a climate-resilient future in Uttar Pradesh and India. The study report was commissioned by Lt. Gen. Yogendra Dimri PVSM, AVSM, VSM (Retd), Vice Chairperson of UPSDMA and was initiated by the former Vice Chairperson of UPSDMA, Lt. Gen. R.P. Sahi, AVSM.

The report on heat thresholds is authored by Dr. Kashif Imdad, PhD, Member, State Advisory Committee, UPSDMA, Dr. Mehebub Sahana , PhD, University of Manchester, Dr. Aarti Krishnan, PhD, University of Manchester, Dr. Upasak Das, PhD, University of Manchester, and Dr. Bhanu Mall , MBBS, MMed, Member, State Advisory Committee, UPSDMA.

Yellow, Orange and Red alerts for Heat Wave
According to the Indian Meteorological Department (IMD), a heat wave is declared when temperatures surpass 40°C in the plains, 37°C in coastal areas, and 30°C in the hills. The other IMD criteria for declaring a Heat Wave involve a departure from the normal temperature by 4.5°C to 6.4°C, while a Severe Heat Wave is declared when the departure exceeds 6.4°C. These criteria closely align with percentile thresholds such as the 75th, 85th, and 95th percentiles. The methodology involves statistical analysis of temperature data to establish thresholds that help identify extreme heat events. The NDMA (2019) advisory recommends issuing colour-coded signals for heatwave alerts, including Yellow, Orange and Red alerts. The IMD’s "departure from normal" concept aligns with the WMO-WHO guidelines for percentile-based thresholds, providing an effective basis for determining Yellow, Orange, and Red alerts based on temperature thresholds. For estimating the district-level heatwave threshold across the country, daily temperature data from 1982 to 2023 was analyses for determining the heat thresholds. The study also proposed the introduction of the “Century Alert," which corresponds to the 99th percentile of temperature data.

The Century Alert
The report also introduced 'Century Alert' which corresponds to the 99th percentile of temperature data. As heat waves have become increasingly common and severe in recent years, posing significant challenges to public health, infrastructure, and ecosystems. To address this pressing issue, meteorological agencies worldwide have developed alert systems to warn individuals and authorities about impending heat-related dangers. Traditionally, these systems have relied on thresholds based on percentiles of temperature data, such as the 75th, 85th, and 95th percentiles. However, as extreme heat events become more frequent and intense, there is a need for a higher level of alert to signal the most severe heat waves. The Century Alert is a new category of heat alert designed to warn the public and authorities about exceptionally severe heat waves. It is based on the 99th percentile of temperature data, meaning that temperatures associated with the Century Alert occur approximately 2.05 days each year on average.