Rtuffli: SIGNAL publish from draft v149

2026-05-30T18:55:27Z

SIGNAL publish from draft v149

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{| class="wikitable" style="float:right; clear:right; margin:0 0 1em 1em; width:320px;"
|+ SIGNAL Earth Structured Data
|-
! Object type
| Damage Signal
|-
! SIGNAL Earth ID
| DS-00119
|-
! Observable type
| Heat index exceedance days (threshold event frequency)
|-
! Unit
| days/yr (number of days per year above heat index threshold)
|-
! Temporal structure
| Annual
|-
! Monitoring backbone
| Meteorological station networks + gridded datasets
|}


{{SignalTerm|type=DS|id=DS-00119|label=Heat index exceedance days (threshold event frequency)}} represent an environmental phenomenon characterized by the annual count of days during which the heat index surpasses a specified threshold. This metric reflects periods of elevated heat exposure that combine air temperature and humidity to assess human-perceived heat stress. Such exceedances are relevant for understanding climate impacts on human health, particularly in the context of heat-related morbidity and mortality. The frequency of these exceedance days serves as an indicator of climate-system forcing effects on heat exposure extremes globally. This signal is situated within the Climate/Health domain and provides a state condition measure of heat stress intensity and duration.

== Geographic / System Context ==
This phenomenon is observed on a global scale, encompassing diverse geographic regions and climatic zones. Heat index exceedance days occur in various environmental settings, from urban heat islands to rural and coastal areas, reflecting local and regional climate variability. The spatial distribution of exceedance days is influenced by geographic factors such as latitude, altitude, proximity to water bodies, and prevailing atmospheric circulation patterns. Understanding the geographic context is essential for assessing regional vulnerabilities and adaptive capacities to heat exposure extremes.

== Monitoring and Measurement ==
Monitoring of heat index exceedance days relies on meteorological station networks that record temperature and humidity data, which are then used to calculate the heat index. Additionally, gridded datasets derived from remote sensing and reanalysis products provide spatially continuous observations. These data sources enable the estimation of the annual frequency of days exceeding defined heat index thresholds. Standard meteorological methods and conventions for measuring temperature and humidity underpin the calculation of the heat index, facilitating consistent monitoring across regions and time periods.

Within the SIGNAL system, this phenomenon is treated as a defined environmental signal whose boundaries and measurement conventions are described below.

== Signal Definition ==
The signal 'Heat index exceedance days (threshold event frequency)' is defined as the annual count of days during which the heat index value exceeds a predetermined threshold indicative of elevated heat stress. The heat index combines air temperature and relative humidity to quantify perceived temperature, reflecting the potential for heat-related health impacts. This signal captures a state change in heat exposure extremes relevant to climate forcing and human health outcomes.

== Boundary Conditions ==
Boundary inclusions encompass all days within a calendar year where the calculated heat index surpasses the specified threshold at any monitored location within the global geographic scope. Boundary exclusions involve days where the heat index remains below the threshold, as well as periods with insufficient or missing meteorological data. The signal excludes transient or sub-daily exceedances that do not meet the daily aggregation criteria and does not account for heat exposure factors beyond temperature and humidity, such as solar radiation or wind speed.

== Aggregation Semantics ==
Geographically, the signal aggregates data from point-based meteorological stations and gridded datasets to produce regional and global summaries of exceedance day counts. Temporal aggregation is annual, reflecting the total number of exceedance days per calendar year. Cross-signal aggregation may involve integrating this signal with related metrics such as heat index spell counts or heat-related mortality rates to provide comprehensive assessments of heat exposure and health impacts. Aggregation methods ensure consistency in spatial and temporal scales to support comparative analyses and trend detection.

== Observational Status ==
Current monitoring of heat index exceedance days is supported by extensive meteorological networks and gridded climate data products, enabling robust annual assessments globally. Data continuity and coverage vary by region, with some areas exhibiting gaps due to limited station density or data quality issues. Ongoing improvements in observational infrastructure and data assimilation techniques are expected to enhance the spatial and temporal resolution of this signal in future SIGNAL releases. These advancements will facilitate more detailed analyses of heat exposure trends and their implications for public health.

== Related Signals ==
* Annual count of heat index exceedance spell events (declared spell rule)
* Heat index
* Heat-related mortality rate


== Key Associated People ==
* '''Sarah E. Perkins-Kirkpatrick''' (University of New South Wales Canberra) [Lead author]



== Sources ==
* [https://www.nature.com/articles/s41467-020-16970-7 Increasing trends in regional heatwaves — 2020]

Heat index exceedance days (threshold event frequency) - Revision history

Rtuffli: SIGNAL publish from draft v149