Podcast: Calculating Threats from Rising Temperatures Using Heat Indexing, with Professor David Romps

March 15, 2024

Extreme Heat: More Dangerous Than We Think?

Extreme heat, one of the adverse consequences of climate change, exacerbates drought, damages agriculture, and profoundly impacts human health. Heat is the top weather-related killer in the United States, contributing to deaths that arise from heart attacks, strokes, and other cardiovascular diseases. As temperatures are projected to increase, so will the risk of heat-related deaths. Urban heat islands, cities with large numbers of buildings, roads, and other infrastructure, are ‘islands’ of hot temperatures due to the reduced natural landscape, heat-generating human-made activities, and large-scale urban configuration. More than 40 million people live in urban heat islands in the United States, with this number only increasing as people continue to move from rural to urban areas. Around 56% of the world’s total population lives in cities. Those living in large cities are more vulnerable to the effects of extreme heat, with research showing an increased mortality risk of 45% compared to rural areas. The risk of heat-related exhaustion and death is a major public health concern that is exacerbated by the climate crisis. 

The National Weather Service is in the process of creating a new interface known as HeatRisk, which uses a five-point scale to monitor the heat-related risk for vulnerable populations based on local weather data and health indicators. By mapping heat risk, climate scientists hope that individuals will now have a better understanding of the safety concerns associated with being outside during times of extreme heat. 

Understanding Heat Index Dynamics

Before stepping outside, most individuals check the daily weather prediction to get a sense of the average temperature. In order to measure the perceived temperature, climate scientists use a heat index, a calculation that combines air temperature and relative humidity to create a human-perceived equivalent temperature. Accurate prediction of the heat index is imperative as every passing year marks the warmest on record, with dangerous extreme heat predicted to become commonplace across arid regions of the world. Therefore, tracking such calculations is necessary in assessing future climate risk. Areas especially vulnerable to extreme heat heavily rely on an accurate prediction of temperature to determine if it is safe to go outside.

However, there are over 300 heat indexes used worldwide to calculate the threat from heat, defeating the potential universality of this metric. Each heat index weighs factors differently, making it difficult to differentiate between various metrics. Dozens of factors are used to estimate the daily temperature based on predictions of vapor pressure, height, clothing, or sunshine levels. In addition, most heat indexes report the temperature assuming that you are a young, healthy adult and are resting in the shade, not in the sun. If outdoors, the heat index could be 15 degrees higher. If you are older, you may not be as resilient during intense temperatures.

As a result, many climate scientists are calling for heat indexes that reveal the apparent risk of being outdoors on any given day. The elderly, children and infants, and those suffering from chronic diseases are more vulnerable to high temperatures than healthy, young adults, which needs to be accounted for when surveying temperature risk. 

Advanced Heat Assessment Tools: HeatRisk and WBGT

The National Weather Service’s HeatRisk index is different from previous models as it identifies unusual heat times and places, also taking into account unusually warm nights. As such, it provides a more universal measure accounting for the degree to which people in the area are acclimated to various heat temperatures. The HeatRisk index can thus be used to gauge levels of danger associated with temperature, potentially altering an individual’s behavioral patterns. 

For those working in outdoor fields, the WetBulb Globe Temperature (WBGT) measure can be particularly useful as a way to measure heat stress as it takes into account temperature, humidity, wind speed, sun angle, and cloud coverage. Different from the heat index, the WBGT includes both temperature and humidity and is calculated for areas in the shade. If not exercising or working outdoors, people can revert to the HeatRisk scale to calculate the potential hazards of being outside for longer periods. 

Heat Indexes are Harder to Calculate Than They Appear

Because scientists have to account for a variety of factors like geography, physics, and physiology, establishing a truly universal heat index is unlikely. For regions like Colorado, creating the criteria for a heat advisory has proven shockingly difficult. Heat indexes typically rely on temperature and humidity, however, the Colorado landscape is so dry that an advisory is very rarely triggered, even during heat waves. In such scenarios, the HeatRisk index provides a better gauge for outdoor safety. Most people underestimate the dangers of extreme heat and often ignore warning messages from local authorities. Educational programs are vital in informing the public on the dangers of extreme heat.

Who is David Romps?

David Romps, UC Berkeley professor of Earth and Planetary Science, is at the forefront of heat index research. Romps has found that those exposed to extreme heat suffer restricted blood flow and are often unable to physiologically compensate. Through his research, Romps believes that heat index calculations often underestimate the potential heat impacts on individuals, with the human body being more susceptible to heightened temperatures than commonly understood. 

Listen to the podcast or read the transcript >