The research, conducted by Alireza Shakiba, Neda Esfandiari, and Babak Mirbagheri of the Center for Remote Sensing and GIS Research at Shahid Beheshti University in Tehran, was funded by the Iran National Science Foundation. Rather than treating heatwaves as a single, uniform phenomenon, the team set out to answer two linked questions: how many distinct types of heatwave behavior exist across Iran, and how does vulnerability to those events change when different analytical perspectives are applied? The answer to the first question was five. The answer to the second was that vulnerability estimates can swing dramatically, with the share of the population living in highly vulnerable areas ranging from roughly 16 percent to as much as 47 percent depending on the scenario and age group considered.

To characterize heatwave behavior, the researchers jointly analyzed four key characteristics of heatwave events: intensity, duration, frequency, and timing. Each of these dimensions matters for different reasons. Intensity determines the physiological stress imposed on the human body and on crops; duration governs whether nighttime cooling can provide relief; frequency controls how often populations are exposed and how little recovery time they receive between events; and timing influences whether heatwaves strike during critical periods such as harvest seasons or peaks in outdoor labor. Analyzed in isolation, these characteristics can give contradictory signals, so the team used principal component analysis, a statistical technique that compresses many correlated variables into a smaller set of independent axes, to distill the essential structure of the data. Clustering techniques were then applied to those components, grouping regions of Iran that share similar heatwave signatures.

The result was the identification of five distinct heatwave regimes spanning the country. What makes this finding striking is that these regimes do not necessarily correspond to Iran’s conventional climatic zones. Average climatic conditions, such as long-term temperature and precipitation norms, have long been the default framework for describing Iran’s environmental diversity, from the humid Caspian coast to the arid central plateau. But heatwave behavior, the study shows, exhibits a spatial organization of its own. Two neighboring regions with similar average climates can experience fundamentally different heatwave patterns, one dominated by rare but intense events and another by frequent, persistent, and seasonally prolonged heat. For risk managers, this means that maps drawn from average climate data are poor guides to where extreme heat will actually bite hardest.

One of the most consequential findings concerns regions with only moderate heatwave intensity. Intuition suggests that where heatwaves are less severe, danger should be lower. The study found the opposite in several areas: moderate intensity combined with high event frequency, long seasonal persistence, and a substantial cumulative heatwave burden produced elevated vulnerability. In other words, it is the total accumulation of heat stress over a season, not the peak of any single event, that erodes the capacity of communities and ecosystems to cope. This cumulative burden perspective aligns with a growing body of international research showing that health impacts of heat depend heavily on event duration and frequency, and that repeated exposure without adequate recovery can be as damaging as isolated extreme spikes.

The second half of the study tackled vulnerability, a concept that in climate research typically combines three elements: hazard, the physical threat itself; exposure, who and what lies in the path of that threat; and sensitivity, the degree to which exposed populations or systems are susceptible to harm. Rather than committing to a single weighting of these components, the researchers built three alternative scenarios representing different orientations: a climate-oriented perspective, a human-oriented perspective, and a resource-oriented perspective. All three scenarios used the same underlying hazard, exposure, and sensitivity components, but they assigned different relative importance to each dimension. This scenario-based design, grounded in multi-criteria analysis methods, allowed the team to test how sensitive their vulnerability maps were to the analytical lens chosen.

The results were dramatic. Depending on the scenario and the age group examined, between approximately 16 and 47 percent of Iran’s population was found to live within highly vulnerable areas. Yet those areas occupy only about 4 to 9 percent of the national territory. This asymmetry, a large fraction of the population concentrated in a small fraction of the land, carries a clear practical message: targeted interventions in a limited number of places could protect a very large share of the people at risk. It also underscores how much the choice of assessment framework matters. A policymaker relying on a single scenario could underestimate the exposed population by a factor of nearly three, misallocating resources for early warning systems, cooling centers, or agricultural support.

Perhaps the most surprising spatial result is where persistent vulnerability concentrates. Areas that showed high vulnerability across multiple scenarios were primarily associated with agricultural landscapes, water-dependent environments, and resource-based livelihoods, rather than being confined to major urban centers. This finding challenges the common focus of heat research on cities, where the urban heat island effect amplifies temperatures in dense built-up areas. Iran’s cities have indeed been the subject of numerous local heat studies, including analyses of spatial inequality in heat exposure in Tehran and thermal comfort in Esfahan and Tabriz. But the new national assessment suggests that rural and resource-dependent communities, whose incomes, food security, and water supplies are directly tied to land and climate, may represent the country’s structurally vulnerable hotspots. Farmers facing heat-stressed crops, communities dependent on dwindling water resources, and populations whose adaptive capacity is limited by economic precarity all fit this profile.

The demographic dimension adds further nuance. By drawing on high-resolution population data that includes age and sex structure, the researchers could assess vulnerability separately for different age groups, an important refinement given that the elderly and the very young face elevated mortality risk during extreme heat. The range of 16 to 47 percent of the population in highly vulnerable areas reflects precisely this variation: different age groups occupy different places and carry different sensitivities, so the geography of risk shifts depending on whose vulnerability is being measured. A single national number would obscure these distinctions and the targeted health interventions they enable.

The broader significance of the study extends beyond Iran’s borders. Heatwaves are intensifying worldwide, and vulnerability mapping has become a central tool of climate adaptation planning. But this research demonstrates that vulnerability is not a fixed property of a place; it is highly sensitive to the analytical perspective adopted, and no single assessment framework can adequately represent it. By integrating heatwave regime analysis with scenario-based vulnerability assessment, the Iranian team has provided a template that other countries can adapt: first understand the distinct behavioral regimes of the hazard, then test how different value judgments about hazard, exposure, and sensitivity reshape the map of who is at risk. The areas that remain vulnerable under every scenario are the most robust targets for adaptation investment, and in Iran those places are the fields, wetlands, and resource-based communities that conventional heat maps have too often overlooked.

Subject of Research: Heatwave regime characterization and scenario-based vulnerability mapping in Iran

Article Title: Heatwave analysis in Iran: identification of regimes and scenario-based mapping of vulnerability

Article References: Shakiba, A., Esfandiari, N., & Mirbagheri, B. (2026). Heatwave analysis in Iran: identification of regimes and scenario-based mapping of vulnerability. Natural Hazards, 122(20), Article 651. https://doi.org/10.1007/s11069-026-08416-y

Image Credits: AI Generated

DOI: 10.1007/s11069-026-08416-y

Keywords: heatwaves, Iran, vulnerability mapping, climate change, principal component analysis, clustering, scenario analysis, population exposure, agriculture, heat stress, adaptation, Natural Hazards