The urban heat island tends to exaggerate extremes of heat in the summer and extremes of cold in winter. While in the summer air conditioning devices[5]​ are increasingly used in domestic, industrial and commercial use, during the winter heating devices (which are sometimes the same, that is, heat exchangers) are used that manage to regulate the temperature of homes and buildings of all types, at the cost of exaggerating the extremes of those temperatures outside said homes or buildings and an increase in energy consumption.[14]​.

This phenomenon is easy to observe in large cities, with multiple air conditioners in the windows of homes that expel warmer and more humid air in the summer and colder air in the winter. Temperature data from digital thermometers that abound in all cities and that are often indicated as examples of global warming by global radio and television stations should be carefully reviewed. Methodologically, different tools must be implemented for the study of urban heat islands, by reviewing different data sources with which these phenomena can be analyzed, and subsequently obtaining the parameters that can influence said heat island.[9]​.

To some extent, urban heat islands are a local example of desert climate, where temperatures can reach 50°C during the day and drop to below 10°C at night. And in the Mediterranean climate we can experience something similar: the excessive daytime heat is offset by a much lower temperature in the early hours of the morning, something that tourists from colder climates should take into account when visiting Mediterranean countries.[15]​[16]​.

The urban heat island (UHI) phenomenon has important repercussions on the health and well-being of the population. Various studies have confirmed its effect on mortality and morbidity in different parts of the world [17]​

.

Daily maximum temperatures correlate better with heat wave-related mortality, while minimum temperatures have a stronger relationship with emergency hospital admissions. In inland cities, a statistically significant association has been observed between maximum temperatures and mortality during heat waves, while in coastal cities, an association has been found between minimum temperatures and the impact on morbidity and mortality, mainly due to the heat island effect. The deaths associated with this phenomenon are mostly preventable. [18]​.

Ambient heat at night can disrupt normal sleep physiology, which can lead to damage to the immune system, increased susceptibility to cardiovascular disease, chronic diseases, systemic inflammation, and psychological and cognitive damage. Some studies suggest a connection between hot nights and mortality in areas of southern Europe.

It is important to highlight that the impact of the heat island on morbidity and mortality cannot be generalized to all cities. Local factors largely determine whether the heat island effect will have a greater or lesser impact on health during heat wave events. Therefore, local-scale studies are required to adequately assess risks and develop effective adaptation strategies.

These studies are essential to create strategic frameworks and specific actions that increase resilience and mitigate the vulnerability of urban populations to extreme heat. Successful adaptation requires local knowledge, competence and capabilities, which can only be addressed through partnerships between individuals, households, communities, local governments and other organizations with the capacity to intervene.

With urbanization, many weather stations have fallen within heat islands. The drift in the artificial data (since it does not record the regional climatology, but rather that forced by the heat island regime) can be eliminated mathematically with adjustment formulas. With the heat island effect, the minimum temperatures are noticeably higher than in the nearby environment and the maximum temperatures are slightly lower, so the average temperature is higher in the city, which also tends to have a higher degree of humidity. As an illustration, the climate in Madrid measured in the Retiro Park, in the center of the city, and at the Barajas Airport, on the outskirts of the Spanish capital. The maximum temperatures are 1.2 °C lower due to the heat island that prevents the arrival of warm winds and solar heating, but the minimum temperatures are 2.1 °C higher, so the average temperature is higher in the center and with a much smaller average daily variation than in the periphery.

The urban heat island tends to exaggerate extremes of heat in the summer and extremes of cold in winter. While in the summer air conditioning devices[5]​ are increasingly used in domestic, industrial and commercial use, during the winter heating devices (which are sometimes the same, that is, heat exchangers) are used that manage to regulate the temperature of homes and buildings of all types, at the cost of exaggerating the extremes of those temperatures outside said homes or buildings and an increase in energy consumption.[14]​.

This phenomenon is easy to observe in large cities, with multiple air conditioners in the windows of homes that expel warmer and more humid air in the summer and colder air in the winter. Temperature data from digital thermometers that abound in all cities and that are often indicated as examples of global warming by global radio and television stations should be carefully reviewed. Methodologically, different tools must be implemented for the study of urban heat islands, by reviewing different data sources with which these phenomena can be analyzed, and subsequently obtaining the parameters that can influence said heat island.[9]​.

To some extent, urban heat islands are a local example of desert climate, where temperatures can reach 50°C during the day and drop to below 10°C at night. And in the Mediterranean climate we can experience something similar: the excessive daytime heat is offset by a much lower temperature in the early hours of the morning, something that tourists from colder climates should take into account when visiting Mediterranean countries.[15]​[16]​.

The urban heat island (UHI) phenomenon has important repercussions on the health and well-being of the population. Various studies have confirmed its effect on mortality and morbidity in different parts of the world [17]​

.

Daily maximum temperatures correlate better with heat wave-related mortality, while minimum temperatures have a stronger relationship with emergency hospital admissions. In inland cities, a statistically significant association has been observed between maximum temperatures and mortality during heat waves, while in coastal cities, an association has been found between minimum temperatures and the impact on morbidity and mortality, mainly due to the heat island effect. The deaths associated with this phenomenon are mostly preventable. [18]​.

Ambient heat at night can disrupt normal sleep physiology, which can lead to damage to the immune system, increased susceptibility to cardiovascular disease, chronic diseases, systemic inflammation, and psychological and cognitive damage. Some studies suggest a connection between hot nights and mortality in areas of southern Europe.

It is important to highlight that the impact of the heat island on morbidity and mortality cannot be generalized to all cities. Local factors largely determine whether the heat island effect will have a greater or lesser impact on health during heat wave events. Therefore, local-scale studies are required to adequately assess risks and develop effective adaptation strategies.

These studies are essential to create strategic frameworks and specific actions that increase resilience and mitigate the vulnerability of urban populations to extreme heat. Successful adaptation requires local knowledge, competence and capabilities, which can only be addressed through partnerships between individuals, households, communities, local governments and other organizations with the capacity to intervene.

With urbanization, many weather stations have fallen within heat islands. The drift in the artificial data (since it does not record the regional climatology, but rather that forced by the heat island regime) can be eliminated mathematically with adjustment formulas. With the heat island effect, the minimum temperatures are noticeably higher than in the nearby environment and the maximum temperatures are slightly lower, so the average temperature is higher in the city, which also tends to have a higher degree of humidity. As an illustration, the climate in Madrid measured in the Retiro Park, in the center of the city, and at the Barajas Airport, on the outskirts of the Spanish capital. The maximum temperatures are 1.2 °C lower due to the heat island that prevents the arrival of warm winds and solar heating, but the minimum temperatures are 2.1 °C higher, so the average temperature is higher in the center and with a much smaller average daily variation than in the periphery.