The first heatwave of the summer is approaching: these are the areas where temperatures will exceed 40 degrees

Official procedures and criteria of AEMET to declare a heat wave

AEMET declares a heat wave when thermal intensity, duration, and spatial extent criteria occur simultaneously, defined objectively based on data from its stations. Technically, there must be at least 3 consecutive days during which, at minimum, 10 % of the stations exceed their local maximum temperature threshold, set at the 95th percentile of the maximums in July and August of the reference period. From this basis, AEMET formally identifies the episode as a “heat wave” and communicates it in its informative notes and climatological reports. Simultaneously, the declaration serves as a reference for Civil Protection and the National High Temperature Plan of the Ministry of Health to activate public health measures.

Thermal criteria: thresholds and percentiles

According to AEMET's technical studies on heat waves in Spain, such as “Heat waves in Spain (update Dec. 2024)” and previous documents like the January 2021 update and the June 2019 update, the definition is based on:

For each reference meteorological station, a local heat wave threshold is calculated: it is the daily maximum temperature corresponding to the 95th percentile of the maximums in the months of July and August over a climatological reference period. Historically, studies have used 1971‑2000, while other organizations' dissemination may refer to 1981‑2010, but the concept is the same: it compares with the hottest 5 % of summer days in the climatology.

This implies that there is no single national value (for example, 40 °C) but different thresholds according to local climatology. However, in media and political practice, episodes exceeding 40 °C in areas such as the Guadalquivir valley or the interior of Castilla‑La Mancha are highlighted, and tropical nights (minimums >20 °C) and even equatorial nights (minimums >25 °C) are recorded, as reported by Demócrata when reporting the first major heat wave of the summer.

Minimum duration and concept of “warm episode”

The duration requirement is twofold:

At the station level, AEMET defines a warm episode as a sequence of at least 3 consecutive days in which the daily maximum temperature is equal to or above the local threshold (95th percentile) of that station. These episodes are first identified at the scale of each measurement point.

Then, AEMET defines a “warm day” at the peninsular/insular scale when, on the same date, at least 10 % of the stations are simultaneously in a warm episode. Finally, a heat wave is considered the sequence of 3 or more consecutive warm days. If there are two sequences separated by only one intermediate day, AEMET's methodology tends to treat them as a single episode, as detailed in technical documentation and presentations such as Rodríguez Ballesteros on heat waves.

Territorial extent and episode characterization

Regarding territorial extent, AEMET does not impose a direct threshold in square kilometers or percentage of provinces. The spatial criterion is incorporated indirectly through the requirement that 10 % of the stations are affected. Subsequently, in its reports, the agency quantifies the extent according to the maximum number of provinces affected on any of the heat wave days, to assess its geographic impact.

This characterization is complemented with data on total duration, absolute maximum temperature, anomalies relative to the average, and comparison with historical episodes, as systematically collected in heat wave reports available on AEMET's website and in outreach spaces such as “Questions and answers about heat waves” on AEMET's blog.

Operational procedure and link with Civil Protection and Health

Operationally, AEMET follows this sequence: monitoring predictions and observations, identifying possible warm episodes, daily evaluation of whether the objective criteria of duration and extent are met, and when confirmed, official declaration of a heat wave in its notes and communications. Before meeting all thresholds, it may refer to the situation as a “very intense heat episode,” something frequently reported by the media, as demonstrated by coverage from Demócrata.

From an institutional perspective, AEMET's technical definition is the one adopted by the Directorate General of Civil Protection for managing the risk of high temperatures, according to its portal on meteorological risks from high temperatures. In turn, the National Plan of Preventive Actions for the Effects of Excess Temperatures on Health, active each year approximately from mid-May to September 30, uses AEMET's information to grade alert levels and health recommendations, directly linking the meteorological technical procedure with political and health responses.

Overall, AEMET's declaration of a heat wave is not a discretionary act but the result of a protocol based on statistical thresholds, percentage of affected stations, and minimum duration, documented in its studies and coordinated with Civil Protection and Health for adopting population protection measures.

Summary answer

The Ministry of Health has an essentially strategic leadership, coordination, and provision of common foundations role regarding heat waves, while direct management mainly falls to the autonomous communities and, at the local level, to municipalities. Based on Article 149.1.16 of the Constitution and the General Health Law, Health sets the state public health foundations, coordinates the National Health System (SNS), promotes national plans such as the National Plan of Preventive Actions against the Effects of Excess Temperatures on Health, defines alert systems and risk communication guidelines. Autonomous communities develop and execute their own heat plans adapted to their territory, with their health, public health, and emergency services, and local corporations act as the first level of social response and protection of vulnerable groups. Consequently, the Ministry does not directly attend to the population but designs the common framework, coordinates surveillance, and ensures a homogeneous response at the state level.

1. Legal framework and general distribution of competencies

The starting point is Article 149.1.16 of the Spanish Constitution, which grants the State exclusive competence over the bases and general coordination of health. At the same time, Article 148.1.16 allows autonomous communities to assume health and public health competencies, which they have done in their statutes.

The Law 14/1986, General Health Law, develops this scheme: it configures the National Health System, defines public health as a shared competence, and specifies that the State reserves functions of coordination, high inspection, establishment of bases, and general planning, while autonomous communities exercise management and execution of services.

2. Direct competencies of the Ministry of Health regarding heat waves

2.1. Normative bases and SNS coordination

Regarding heat waves, the Ministry exercises its general competencies of:

• Setting public health bases: common criteria on thermal risk surveillance, definition of vulnerable groups, alert levels, and main lines of health intervention.
• Coordination of the National Health System: using the Interterritorial Council of the SNS to agree on joint responses, action criteria, indicators to monitor, and shared information mechanisms among communities.

2.2. National Heat Plan and state planning

A key tool is the National Plan of Preventive Actions against the Effects of Excess Temperatures on Health. Under this name, a state framework is articulated that:

• Establishes the general objectives of preventing heat impact on health.
• Defines a risk level system for high temperatures and plan activation periods.
• Sets common recommendations for autonomous health administrations and other sectors (social services, civil protection, etc.).
• Serves as a reference for communities to develop or update their own autonomous prevention plans.

2.3. Early warning systems and epidemiological surveillance

In public health, the Ministry participates in and coordinates:

• Early warning systems integrating meteorological data (in collaboration with other ministries competent in climate and meteorology) with health and demographic information.
• National epidemiological surveillance of heat effects: monitoring mortality and morbidity associated with extreme temperatures, aggregated analysis of data sent by autonomous communities, report preparation, and health impact evaluation.
• Setting indicators and registration methodologies so data are comparable across territories.

2.4. Risk communication and protocol development

The Ministry also has key responsibilities in:

• State-level risk communication: general prevention messages directed at the population (hydration, sun protection, limiting physical effort, attention to elderly, chronically ill, infants, etc.), disseminated in coordination with other administrations.
• Common guides and protocols for health professionals and emergency services: recommended triage criteria, heat stroke management, resource organization during peak demand periods, as well as recommendations for residences and social-health centers.
• Training and technical support to autonomous communities through consensus documents and public health technical materials.

3. Competencies of autonomous communities and local corporations

3.1. Autonomous communities

Based on the above, autonomous communities are primarily responsible for operational management against heat waves. Their responsibilities include:

• Developing and applying autonomous plans for prevention and action, adapting the National Plan to their climate, population distribution, and health resources.
• Organizing healthcare (primary care, hospital, emergencies) and public health services responsible for controlling and mitigating high temperature effects.
• Activating and managing alert and health response systems in their territory, coordinating with emergency and civil protection services.
• Developing specific information campaigns for their population, adjusting state messages to the autonomous context.

3.2. Local corporations

Municipalities and provincial councils have a proximity role focused on:

• Detecting and protecting especially vulnerable groups (elderly living alone, homeless people, population in substandard housing).
• Implementing local devices (cooling public spaces, enabling climate shelters, reinforcing social services and home care during extreme heat episodes).
• Disseminating alerts and recommendations from the autonomous health authority and the Ministry within the community fabric (neighborhoods, civic centers, neighborhood associations, etc.).

4. Key idea

In summary, the Ministry of Health does not replace autonomous communities in daily health care related to heat waves but plays a decisive role in defining the common public health framework, coordinating the response of the entire National Health System, establishing alert systems, promoting the National Plan, and ensuring coherent risk communication throughout the territory.

Brief answer

Besides the Ministry of Health's National Plan of Preventive Actions against the Effects of Excess Temperatures on Health, most autonomous communities have developed their own plans or protocols for prevention against extreme heat, aligned with that state framework. Among the best-documented cases are Aragón, Euskadi (Basque Country), La Rioja, and the Community of Madrid, which have specific autonomous plans on “heat and health” or “extreme temperatures.” These instruments set temperature thresholds, alert levels, and surveillance and communication circuits, with special focus on vulnerable groups. Additionally, other communities such as Andalusia, Valencian Community, or Extremadura have articulated sectoral measures (tourism, agricultural work, meteorology) that complement the national strategy.

Clearly identified autonomous plans

Aragón

Aragón has an Action Plan for the prevention of extreme temperatures, periodically activated during the risk season, explicitly defined “within the framework of the National Plan.” Its central objective is to reduce the impact of extreme heat on the population's health, using a system of provincial thresholds and risk levels with associated actions. In the most recent version identified (2023 campaign), the Government of Aragón introduced technical updates: updating threshold temperatures for each province, revising the alert algorithm, and using the maximum temperature with a 3-day forecast (instead of maximums and minimums at 5 days), maintaining the same structure of levels and types of action. All this positions Aragón as an example of a community that adapts and refines the state plan methodology to its climatic and epidemiological reality (Aragón).

Euskadi (Basque Country)

Euskadi has a Heat Plan 2026 for preventing the effects of extreme temperatures on health, developed by Basque health authorities. The document itself highlights that autonomous plans have evolved by incorporating epidemiological criteria in threshold definitions, strengthening epidemiological surveillance, and greater territorial disaggregation in isoclimatic zones. Its contents include a detailed framework of objectives, actions, and indicators, along with surveillance, alert, and information systems activated at different risk levels, and specific recommendations for the population, health services, social services, and other involved agents. Thus, the Basque plan operates as the autonomous equivalent of the National Plan but adapted to Euskadi's climatic and organizational particularities (Euskadi).

La Rioja

La Rioja has the Alert, Prevention, and Control Plan for the Effects of Excess Temperatures on Health 2025, conceived as a specific component of the Epidemiological Surveillance Network of La Rioja. Its general objective is to reduce the impact of extreme heat episodes through surveillance, prevention, and control of their effects on morbidity and mortality. The plan establishes a Health and Environmental Information and Surveillance System, foresees the dissemination of advance information to citizens and professionals, and uses alert levels based on thermal thresholds to activate proportionate measures to the risk. It is a clear example of structured and formalized autonomous adaptation of the National Plan approach (La Rioja).

Community of Madrid

The Community of Madrid maintains a specific “Heat and health” device, following the general logic of the National Plan but with its own development. Autonomous documentation identifies as the main objective to reduce morbidity and especially mortality associated with unusual temperature increases. Common measures include issuing alert bulletins, identifying shade spaces and water points, reinforcing sun protection, and adapting activities during the hottest hours, especially for exposed groups (e.g., children in educational centers or elderly people). This action scheme is articulated from the Ministry of Health and complements national guidelines (Community of Madrid).

Other communities and common features

Beyond these examples with clearly located documents, information collected by the Spanish Federation of Municipalities and Provinces indicates that most autonomous communities have some own plan or protocol against high temperatures, generally coordinated with the National Plan (FEMP). The Ministry of Health also points out that the National Plan's design is made to be implemented and adapted by the autonomous communities through their public health services (National Plan 2025), reinforcing this idea of territorial deployment.

In parallel, there are local and sectoral plans that, without being strictly “autonomous heat plans,” act as complements: action guides against high temperatures for municipalities (Network of Cities for Climate), educational or labor protocols, and technical materials developed by communities or entities in the educational and health fields (example of a center protocol). Overall, it can be said that the National Plan functions as a common framework and that, from it, communities such as Aragón, Euskadi, La Rioja, and Madrid —among others— have developed similar or complementary plans, with alert, surveillance, and communication structures very close to each other (AdapteCCa).