Excess Heat & Excess Cold

Project Overview

Hazardous heat and cold cannot be characterized by temperature alone. Humidity and wind affect how atmospheric conditions are experienced, while the significance of a particular temperature also depends on location, season, event duration, and the conditions experienced during the preceding several weeks.

This Excess Temperature Project developed and evaluated measures of excess heat and excess cold based on apparent temperature. These measures identify conditions that are unusually hot or cold relative to locally defined thresholds and incorporate an acclimatization component that accounts for recent weather conditions. Together, these elements provide a unified duration–intensity framework for characterizing potentially hazardous temperature conditions.

This work was supported by the National Oceanic and Atmospheric Administration from 2022 through 2026 under the project Excess Heat and Excess Cold Factors: Establishing a Unified Duration–Intensity Metric for Monitoring Hazardous Temperature Conditions in North America (Grant Number: NA22OAR4310142). It was later expanded to the entire globe.

Building on Earlier Research

This project extended research initiated through an earlier NOAA award funded in 2017. That work developed absolute and seasonally relative measures of heat and cold events for North America and examined their historical trends.

The 2022 project expanded this foundation by evaluating the representation of apparent temperature in several major reanalysis datasets, examining recent changes in hazardous heat and cold across the contiguous United States, assessing county-level population exposure and social vulnerability, and extending the resulting data products globally.

Global Excess Temperature Dataset

The primary public data product from this project is a global daily dataset of absolute and seasonally relative excess apparent-temperature factors and events covering 1940–2024.

The dataset contains four complementary types of event identification:

• Absolute excess heat events (EHE)
• Absolute excess cold events (ECE)
• Seasonally-relative excess heat events (REHE)
• Seasonally-relative excess cold events (RECE)

The absolute measures identify sustained conditions exceeding locally defined hot or cold thresholds. The seasonally-relative measures identify unusually hot or cold conditions for a particular time of year, including events that may occur outside the climatological core of summer or winter.

All measures are calculated from apparent temperature, which combines air temperature, atmospheric moisture, and wind speed to better represent human-perceived thermal comfort. The calculations also include an acclimatization component that compares current conditions with those experienced during the preceding 30 days.

Access the Data

The complete dataset is publicly available through Zenodo:

Access the Excess Heat & Cold Factors and Events dataset

The repository contains monthly NetCDF files on the global ERA5 grid. The files include daily apparent temperature, excess heat and cold factors, seasonally relative excess heat and cold factors, daily event classifications, event-level information, spatial coordinates, grid indices, and time variables.

Please consult the Zenodo record for the complete metadata, file documentation, recommended dataset citation, and terms of use.

Major Research Findings

The project produced three linked studies that evaluated the input data, applied the excess-temperature framework, and investigated the societal implications of changing hazardous-temperature conditions.

Evaluating Reanalysis-Based Apparent Temperature

The first study compared apparent temperature from ERA5, MERRA-2, NARR, and the 20th Century Reanalysis with station observations across the contiguous United States. ERA5 provided the strongest overall representation of both daily apparent temperature and unusually hot and cold conditions, supporting its use as the basis for the project’s expanded gridded analyses and global dataset.

Ibebuchi, C.C., Lee, C.C., Silva, A.L., and Sheridan, S.C. (2024). Evaluating Apparent Temperature in the Contiguous United States From Four Reanalysis Products Using Artificial Neural Networks. Journal of Geophysical Research: Machine Learning and Computation, 1, e2023JH000102. DOI: https://doi.org/10.1029/2023JH000102

Recent Changes in Hazardous Heat and Cold

The second study compared excess-temperature events derived from ERA5, MERRA-2, and NARR. The results showed geographically varying patterns of change, but the datasets generally agreed that excess heat events have become more frequent across portions of the western and southern United States. Excess cold conditions have generally declined, with seasonally relative cold conditions decreasing across a particularly broad area and at a greater rate than the corresponding increase in heat.

Ibebuchi, C.C., Lee, C.C., and Sheridan, S.C. (2024). Recent Trends in Extreme Temperature Events Across the Contiguous United States. International Journal of Climatology 45(2), p.e8693. DOI: https://doi.org/10.1002/joc.8693

Population Exposure and Social Vulnerability

The third study translated the gridded climate results to the county scale and evaluated the intersection of increasing hazardous heat, population exposure, and social vulnerability. Increasing heat exposure was concentrated particularly in populous counties in the southern and western United States. The study also demonstrated the importance of considering seasonally relative heat, which can identify hazardous conditions occurring outside the period when the most intense summer heat is normally expected.

Ibebuchi, C.C., Lee, C.C., and Sheridan, S.C. (2026). Risk Assessment of Counties in the Contiguous United States Impacted by Increasing Frequency of Hazardous Temperatures. Natural Hazards, 122(14). DOI: https://doi.org/10.1007/s11069-025-07800-4

Project Outcomes

The project established a consistent framework for evaluating excess apparent-temperature conditions across locations, seasons, and climate regimes. Its principal outcomes include:

• A publicly available global daily dataset covering 1940–2024
• Validationing apparent temperature across multiple observational & reanalysis products
• Analysis of changes in absolute and seasonally relative excess heat and cold
• County-level assessment of hazard, population exposure, and social vulnerability
• Peer-reviewed publications documenting the methods and major findings
• Reusable data products and methods for climate, health, environmental, and hazard research.

Funding and Project Team

This research was funded by the National Oceanic and Atmospheric Administration Climate Program Office under Award NA22OAR4310142: Excess Heat and Excess Cold Factors: Establishing a Unified Duration–Intensity Metric for Monitoring Hazardous Temperature Conditions in North America

Principal Investigator:
Cameron C. Lee, Kent State University

Co-Investigators:
Scott C. Sheridan, Kent State University
Karin Gleason, NOAA National Centers for Environmental Information

Postdoctoral Scholar:
Chibuike Chiedozie Ibebuchi

The project also supported research collaboration, professional development, presentations to scientific and stakeholder audiences, NOAA webinar participation, student research, and consultation with an external project advisory board.