Climate of Spain

Map of different climate regions in Spain

Continental Mediterranean Mediterranean coast Mediterranean semi-arid Continental ocean Coastal ocean Mountain Subtropical

The Iberian Peninsula is located in a prominent place within the general atmospheric circulation, which does not remain static but rather there are different movements from north to south, depending on the season of the year. The peninsula is located in a temperate zone, not having homogeneous climatic characteristics as it is a mixing zone between warm air zones and cold air zones (subtropical and polar).

The varied orography of Spain, as well as its geographical location, in the middle latitudes of the temperate zone of the Northern Hemisphere, means that the country has a remarkable climatic diversity. Thus we went from places with mild temperatures, around 15 °C, to others that exceed 40 °C in summer, and from places with a humid oceanic climate with annual rainfall of more than 2,500 mm to places with a desert-like Mediterranean climate. that do not exceed 200 mm per year, such as Cabo de Gata, with 150 mm per year.

However, there are a number of general features that can be summarized in the following points:

• In the lands of the interior, the values descend from Poniente to Levante.
• Temperatures increase from north to south. The northern part of the Meseta presents values between 10 °C and 15.5 °C, and the southern zone, between 12.5 °C and 15 °C.
• January is usually the month with the lowest average temperature, while August is the month with the highest average.
• The temperatures of the Mediterranean waters are higher than those of the Cantabrian. In the first, the average is between 15 °C and 18 °C, while in the second, it is around 14 °C.
• The thermal amplitude is greater in the interior of the Meseta, where at times it reaches 20 °C, while in places like the Canary Islands that amplitude is smaller, and between the warmest month and the coldest there is hardly variation of 5 °C.

The different climates of Spain

Traditionally, four major climates have been classified in Spain: oceanic, Mediterranean (with some variations), subtropical and mountain. Each influences a clearly defined geographical area:

• The Atlantic climate: this climate extends throughout the north and northwest of the peninsula, from the Pyrenees to Galicia. It is characterized by the abundance of rains, which usually exceed 1000 mm, distributed regularly throughout the year. For that reason, the landscape is very green. Temperatures are usually mild due to the proximity of the sea: in winter they range between 12 °C and 15 °C and in summer they are around 20 to 25 °C. The representative cities are San Sebastián, Gijón, Santander, Foz, Vigo or Oviedo. However, and precisely because it is mainly coastal cities, the humidity usually increases the minimum and maximum temperatures, especially in the south of Galicia. Experts have concluded that in the city of Vigo 52 °C were reached as a thermal sensation (The heat wave of July 2013), due also to the little difference between day and night temperature.

• The Mediterranean climate: this climate is the predominant one in Spain, as it extends along the entire Mediterranean coastline, the interior of the peninsula and the Balearic archipelago. However, there are considerable differences between areas and areas, resulting in three subdivisions:

1. The typical Mediterranean climate: covers most of the coast of the same name, some areas of the interior, Ceuta, Melilla and Balearic Islands. Rains are irregular, between 400 and 700 mm per year, and are concentrated especially in autumn and spring. Winters are short and soft while summers are long and hot. The average annual temperature is around 15 °C and 18 °C. The representative cities are Barcelona, Valencia, Palma de Mallorca or Castellón de la Plana.
2. The Mediterranean climate with cold winter (also called "landerized Mediterranean"): it is located in the Central Meseta, the depression of the Ebro, part of the Guadalquivir and the interior of the Valencian Community. It is characterized by very extreme temperatures, between 25 °C and -13 °C. The winters are long and very cold, where the minimum temperatures can go down to -5 °C or less, and the very hot summers, where every year they exceed 35 °C, and even 40 °C on some occasions. In addition, rainfall is scarce, around 500 mm, and appears in the form of a storm in the months of July and August. The representative cities are Madrid, Albacete, Valladolid or Granada.
3. The dry Mediterranean climate: appears mainly in the southeast of the territory, in the areas of the Region of Murcia, Alicante and Almería. Rains are extremely low, less than 300 mm a year, making these areas very arid, and long periods of drought are frequent. Temperatures are similar to those of the typical Mediterranean, although summer heat is usually more intense. The representative cities are Alicante, Murcia, Almería, Elche, Orihuela or Cartagena.

Climate classification of Köppen.

• The subtropical climate: this climate only appears in the Canary Islands due to its proximity to the Tropic of Cancer and the arid coast of Africa. It is characterized by the presence of the Alisian winds and the currents of cold water. Temperatures are warm all year round, between 22 °C and 28 °C of average, while precipitation can be abundant or few, depending on the area, are concentrated in winter. For that reason, there are no rivers in the Canary Islands and when it rains they form torrents. The representative cities are Santa Cruz de Tenerife, La Restinga or Las Palmas de Gran Canaria.

1. The humid subtropical climate: is characterized by warm temperatures throughout the year and variable and abundant precipitations, being able to exceed 700 mm per year. It is given in the north of the most mountainous islands, where the humidity of the Alisian winds is maintained. The representative cities are La Orotava or Los Realejos.
2. The mountain climate: is characterized by cold temperatures in general, or very cold depending on the altitude, which can come down from 0 °C and produce occasional snowfalls. Precipitations are quite rare, as the terrain is too high for the smooth winds to affect. It occurs in the highest areas of Tenerife, La Palma and Gran Canaria.
3. The dry subtropical climate is characterized by mild and constant temperatures throughout the year and very low rainfalls (100 mm to 250 mm). It is given in most of Fuerteventura and Lanzarote, and in the south of Gran Canaria, Tenerife and La Gomera.
4. The desert climate is characterized by mild temperatures throughout the year with little thermal oscillation during the day and night and extremely low rainfall (less than 100 mm). It is mainly given in the most arid areas of Fuerteventura and Lanzarote, although where it is most noticeable is in Fuerteventura. One of the most desert sites in Fuerteventura is Gran Tarajal, since only 62.6 mm of an annual average are recorded. That precipitation data has been obtained for 17 years.

• The mountain climate: appears in the large mountain systems such as the Pyrenees, the Central System, the Iberian System, the Penibbean mountain range and the Cantabrian mountain range. Winters are very cold and fresh summers. Precipitations are very abundant as the altitude increases and, in general, in the form of snow. The slopes of the mountains that look north are colder. Some representative locations of this climate are Viella, Benasque, Somosierra or Trevélez.

It stands out its own situation between the Atlantic and the Mediterranean, in this context the Atlantic has the main role because it is responsible for the entrance of the west wind. The Mediterranean has little influence on climatic diversity, it only affects the coasts and the creation of cold drops.

The duality of behavior between the coast and the interior also stands out, with phenomena occurring on the coasts such as breezes, humidity and reduced thermal amplitude. Inside there is more thermal amplitude and less humidity, which is due to continentality. The relief and its arrangement that prevents the free passage of air masses also influences, here the Föhn effect occurs.

The municipality of Montoro (Córdoba) holds the temperature record in Spain, with 47.4 °C on August 14, 2021, based on data from the State Meteorological Agency (Aemet). However, the city with the highest average annual temperature is Seville with 19.2 °C, as well as the highest average in summer, 28.2 °C in July Vega de Liordes, an enclave in the Picos de Europa sector of Leon belonging to the municipality of Posada de Valdeón registered -35.8 °C on January 7, 2021.

In 2009, the average temperature for the month of August in Spain was 25.2 °C, that is, 1.9 °C above the average for the reference period (1971-2000), making it the eighth month August 2009 the second-warmest August of the XXI century and the third-warmest since 1961, behind 2003 and 1991, which had positive anomalies of 2.8 and 2 °C respectively, according to the State Meteorological Agency. In the Balearic and Canary Islands, August was "very warm", although temperatures were 0.8 and 1.2 °C, respectively, higher than the global values for the reference period. In 2003 there was an anomaly of 2.8 °C and 2009 was only one tenth of the second warmest year (1991), which registered an average temperature 2 °C higher than the average for the period, that is, August 2009 narrowly missed the second warmest between 1971 and 2000. Ciudad Real was 0.6°C above 28°C in 2003; Albacete higher by 0.2 tenths and Teruel 0.5 tenths more. The archipelagos registered 0.8 °C above the 25.2 °C of the Peninsula, which shows a positive trend, somewhat more attenuated by the maritime influence. On the contrary, Mediterranean cities such as Valencia and Murcia as well as in areas of the peninsular northwest had an average temperature in August one degree Celsius lower than the rest. The second half of August was the warmest in the last 50 years in Extremadura, the center of the peninsula, western Castilla-La Mancha and northwestern Andalusia. On September 3, 2009, very warm maximum temperatures were recorded throughout the Mediterranean area, with Murcia reaching 38.7 °C and in Tortosa the thermometers rose to 38 °C, their maximum temperature for September in all records. The previous record in this town was 37 °C on August 25, 1983. For its part, Santander broke its absolute maximum for August with a value of almost 36 °C.

Factors

Action centers that affect the climate of Spain.

Average annual rainfall by cities (1971-2000)

Dynamic factors

Action centers

They are the ones that cause precipitation, humidity and winds. Within the dinaminación several elements exist:

• Within the atmospheric circulation is the stream in jet, which is an airflow that is around 50° north latitude with a speed of 250 km/h and is around 10000 m high. It has a transfer from north to south depending on summer or winter. In the summer, the Iberian peninsula is influenced by tropical air masses. In winter it descends from latitude and the tropical air masses descend and lets the peninsula influence cold winds.

• The second dynamic element is the action centers that refer to high and low pressure centers.

In areas of high pressure (anticyclones), the air rotates clockwise and the air is above 1013 hPa. Among them are:

• The Azores anticyclone that is the one that most affects the peninsula, has its origins in the high subtropical pressures that move north and south. When they reach the north it causes stable time on the peninsula, usually occurs in summer, in autumn and winter it descends further south and there is unstable time. It is the cause of the entrance of warm winds on the Iberian peninsula.
• Atlantic polar anticyclones that are a prolongation of the Azores in their northern part and exert their influence in winter, dragging marine polar air and causing Northern situations.
• The Siberian anticyclone, which forms in Siberia from masses of cold continental air, as it runs through continental areas this anticyclone will have dry winds and will provide the creation of strong frosts in the interior and snowed in the coasts if it is associated with a Mediterranean eraser in winter.

The most important storm is the one in Iceland, which is located between the anticyclone of the Azores and the Polar Atlantic. This storm throws masses of cold polar air that, upon reaching the sea, become loaded with humidity and cause strong instability.

The depression of Genoa or the Baja Balearic Islands

It is constituted in the autumn months, the formation process arises from continental cold air masses that, when they reach the sea, are loaded with humidity and cause a strong instability and will create the cold drop. In the winter months, it expels the continental polar air mass from its rear edge towards the Peninsula and the Balearic Islands, causing strong rough seas in the Balearic Sea and snowfall on the coasts of Catalonia, the Balearic Islands and the Eastern Cantabrian Sea.

The Azores Depression

It is caused by the collision between the cold polar air mass and warmer masses creating instability, these storms are very common in the formation of storms that enter through the Gulf of Cádiz that will have their origin in this depression.

The Saharan Depression

Originated by the strong heat that causes hot air to rise and contact colder areas and cause instability, an anticyclone in height will give rise to heat waves. The same origin as this Saharan depression will have some depression in the interior of the Iberian Peninsula. especially in summer, these depressions are of thermal origin.

The Atlantic Depression

It is associated with maritime polar air, especially in winter, autumn and spring, causing rain on the peninsula. The temperatures will be milder than the winds of the depression of Iceland being in lower latitudes

Air mass

The greater or lesser influence of these storms depends on the existence of air masses that are influenced by centers of action and have their own characteristics, when it is cold it will be called polar or arctic, when it is warm it will be tropical, if it is wet it will be maritime and if it is dry it will be continental.

Arctic-maritime air mass

It is cold and humid, it originates in the Arctic basin, and it rarely affects the Iberian Peninsula. Coming from the Arctic on the journey of this mass to the south, it is filled with humid air and when it reaches the peninsula it will bring very low temperatures and precipitation in the form of snow in the north of Spain.

Maritime Polar Air Mass

It comes from the North Atlantic after traveling a long stretch of ocean, it is less cold than the Arctic, as it crosses the ocean it fills with humidity, when it enters the peninsula it gives as a consequence humid and fresh air and when its influence occurs a storm gives rise to rainy weather, when associated with an anticyclone it gives rise to cool and clear weather. When these air masses descend and walk across the Azores sea, it heats up and produces a high instability that causes it to lose its properties and evolve towards other types of air masses.

Polar-continental air mass

It is cold and dry, it comes from Central Europe and Russia, the origin is located in a polar or arctic air mass that has become stagnant in the continental areas of Europe if the Siberian anticyclone is added to this air mass It can get quite freezing cold, the fact that it is stagnant in a continental zone means that it is not so humid. When it reaches the Mediterranean, it is invaded by humidity and then it enters the peninsula causing a wave of cold and on the plateau it gives rise to copious snowfalls, it has its maximum influence in winter.

Air mass is tropical-maritime

It has influence in summer, providing strong stability.

Tropical-Continental Air Mass

It is hot, dry and suffocating, it is the heat wave, it comes to produce mud rains, its greatest influx is summer.

Fronts

They are contact zones between two air masses with different characteristics. In the Iberian Peninsula, the polar front that puts the tropical air mass in contact with the polar air stands out. This polar front, when it passes in the peninsula, gives rise to precipitation and will gradually weaken. It is highly conditioned by the dynamics of the action centers (anticyclone and storm). The storms are the main factor for this front to cross the peninsula from west to east, it is normal for it to pass from northwest to southeast but it can also do so to the southeast due to the Azores depression. There are other fronts but they are less important, of which the Mediterranean stands out, which gives rise to a discussion about whether it is a prolongation of the polar or a front itself, now it is accepted that it is a prolongation of the polar caused by the contact of cold air from the Hispanic peninsula with the warm air of the Mediterranean. This front will be very important in the cold drop. The third front is that of the Alisios formed from the contact of the maritime tropical mass of the Azores with the continental tropical, it is located in North Africa, it influences the Canary Islands and the Iberian Peninsula in the western half of Andalusia. The last front will be the Arctic that arises from the contact of the maritime polar mass and the Arctic, in a very exceptional way it will influence the Iberian Peninsula.

Geographic factors

The presence of the Mediterranean and the Atlantic stand out, as well as the peripheral disposition of the relief. The main geographical factor is continentality. These factors have a lot to do with the latitude of the Iberian Peninsula, which, being in the temperate zone, gives rise to strong heterogeneity in terms of climate.

The very layout of the relief determines that the mountain ranges serve as a barrier to the introduction of different air masses. These mountainous barriers cause the Föhn effect that favors the continentality of the Iberian Peninsula, which is caused by the relative distance from the sea. Continentality causes a great thermal amplitude.

Synoptic situations

Weather is the state of the atmosphere that results from the combination of various factors such as humidity, pressure and temperature at a precise moment. The types of weather is the reiteration of similar atmospheric situations.

Convective situations are those where vertical air movements predominate; in anticyclone situations the air will be descending and in storms it will be ascending. This vertical movement sometimes produces stormy phenomena, the hot air that is on the surface rises and due to contact with a cold air mass, water condensation occurs, which will give rise to convective rains. Advective situations are defined by the horizontal movement of air coming from different places.

In Spain there will be predominant situations:

Situation of the North

It is determined from the location of an anticyclone in the North Atlantic and a storm in Western Europe. What the anticyclone does is prevent the arrival of storms from the west. What the storm does is introduce cold air into the Iberian Peninsula from north to south.

Northeast Situation

It is very similar to the previous one, there is also a North Atlantic anticyclone but it invades part of Europe. There will also be a storm in the Mediterranean that will cause the peninsula to be affected by continental polar air found in the interior of Europe. The type of weather that will predominate will be cold and dry and will cause frost.

Situation of the East or Levante

Cloud formed by the wind of Levante in Gibraltar.

It will lead to different locations. There is an anticyclone that extends from the Atlantic to the interior of Europe. The storm will be located in North Africa. This will occur in spring and autumn and the most important consequence is that the Iberian Peninsula will be invaded by a mass of Mediterranean air that, in general, is warm and humid, which causes rainfall, although of little intensity. If this mass of warm air is at altitude, it will give rise to very stormy or cold drop phenomena. The wind in the Strait of Gibraltar will have to be taken into account.

Situation of the South

It will always be favored by the location of a storm on the western Spanish coasts and an anticyclone is going to settle in the Mediterranean. Between these two centers of action, the main consequence is the rise of dry winds from North Africa (continental tropics), which in summer translates into heat waves. If there is a trough or mass of cold air in height, heavy downpours will occur in the south.

West Situation

It is characterized by the location of a very strong storm in the Atlantic. This depression will launch polar air masses to the Iberian Peninsula. This storm will accompany the cold front that will sweep the peninsula from west to east. The type of weather that will predominate is precipitation with high humidity and mild temperatures. This kind of weather will be very important in autumn and winter.

Northwest Situation

It will be characterized by the presence of an anticyclone in the Atlantic that will be very close to the southwest of the peninsula and a center of low pressure will be located in the British Isles. This is accompanied by cold fronts that will cross the Iberian Peninsula and may be accompanied by cold fronts that will cross the peninsula. These fronts can pass more or less intensely depending on the location of the anticyclone, this will cause the most affected area to be the Cantabrian coast. The cold front will be pushed up by an anticyclone, which will cause precipitation on the Cantabrian coast.

Southwest Situation

It is characterized by the location of a storm in the southwest of the peninsula. In most cases, this storm will be accompanied by a cold front and a trough of the jet stream will also accompany it in height. This situation is temporary, there are widespread rains in the Iberian Peninsula. The cold front also crosses the peninsula from west to east. It will predominate in winter.

Elements of weather

These are the conditions that, together with climatic factors, define the types of weather (temperature, pressure, precipitation, humidity, insolation...).

Temperature

The main characteristic is its uneven behaviour, closely related to atmospheric circulation and geographical factors.

Mean annual temperature in Spain

Average annual temperature map (°C) in Spain during the period 1981-2010.

The estimated average temperature over Spain in the reference period 1981-2010 is approximately 15.1 °C. However, this average varies considerably from one place to another. Several factors affect the uneven distribution of these average temperatures:

• Influence of the sea that softens the temperatures, as we move away from the coast hardens, the summers will be warmer and the coldest winters. The North Plateau is colder than the South as it is closed by mountainous massifs and the South is influenced by the Atlantic.
• Latitude is very related to insolation. In general, the higher the latitude (the longer the equator is) the lower the average temperature. This factor is noted a lot in the Canary Islands regarding the rest of Spain. In fact, the warmest places in Spain are located on these islands, which make up the less latitude Spanish territories.
• The altitude. At higher altitude it is colder in a ratio of 0.65 °C per 100 m of rise.

Distribution of average temperatures in the Iberian Peninsula:

1. Less than 10 °C of average annual temperature: it is very limited, it is only located in mountainous areas and its surrounding areas (especially in the north plateau) at higher altitude. It is mainly given in the Pyrenees, Cordillera Cantábrica, Montes de León, Sistema Central, Cordilleras Béticas y Sistema Ibérico, and in Canarias it is only given in high altitude areas of Tenerife and La Palma
2. Between 10 and 12.5 °C of average annual temperature: its location is located in the northern peninsula, especially in medium altitude zones, including most of the North Plateau, with a prolongation by the Iberian System. It is also given in medium-high altitude zones of the Béticas mountain ranges. In the Canary Islands it occurs in areas of medium-high altitude of Tenerife, La Palma, Gran Canaria, El Hierro and La Gomera.
3. Between 12.5 and 15 °C of average annual temperature: is the most widespread. It is mainly given in the South Meseta and in the lower altitude areas of the North Meseta, in low altitude zones of the north peninsular, in much of the Depression of the Ebro and in medium-low altitude areas of the Béticas Cordilleras
4. Between 15 and 17.5 °C of average annual temperature: It is given in much of Andalusia, in most of Extremadura, in the lower altitude areas of the South Meseta and the Depression of the Ebro, on the Mediterranean coast of the north and much of the Valencian Community and Murcia and in most of Mallorca and Menorca. In the Canary Islands it is given in areas of average altitude of all islands except in Lanzarote and Fuerteventura.
5. Between 17.5 and 20 °C of average annual temperature: it is given in the Depression of Guadalquivir, in most of the Mediterranean coast of the center and south peninsular, in Extremadura mainly in the Tagus Basin and in most of Ibiza and Formentera and to a lesser extent in Mallorca. In the Canary Islands it is given in all islands in medium-low altitude zones and to a lesser extent in coastal areas.
6. More than 20 °C of average annual temperature: It is given only in coastal areas of the Canary Islands, especially in Lanzarote, Fuerteventura, Gran Canaria and southern Tenerife.

Average monthly temperature

The coldest month is January, the low temperatures are related to the fact that the day lasts less and the polar air masses have more influence. The main characteristics are the drop in temperatures from north to south and from the periphery to the interior. The eastern part of the peninsula is where the most abrupt temperature changes related to the orography itself occur (Mediterranean and mountains): The area closest to the Mediterranean is warmer than the Atlantic coast, this temperature difference is balanced when we move towards the North. The northern sub-plateau is colder than the south. The last characteristic is the strong contrast between the Ebro depression (from 4 to 6 °C) and that of the Guadalquivir (from 8 to 12 °C) due to the fact that the Ebro depression is embedded by various mountain ranges and the continentality is superior, latitude also matters. That of the Guadalquivir receives the influence of warm air masses as it is not enclosed.

The warmest month is July in inland areas and August in coastal areas. In summer the anticyclone of the Azores is especially important, tropical-continental air masses will also be introduced from the south. Characteristics:

1. The most remarkable feature is that in the south half temperatures increase from the coast to the interior which contrasts with what happens in the north.
2. The influx of the Azores anticyclone is of different magnitude, in the Cantabrian Cornisa the influence is restricted, in the center and south increases more and the temperatures rise from north to south.
3. The Mediterranean coast (Barcelona 24.4 °C, Alicante 26.0 °C, Malaga 26.0 °C and Almeria 26.7 °C in August) is warmer than Atlantic (San Sebastián 19.5 °C, La Coruña 19.6 °C, and Santander 20.3 °C in August).
4. The north subset is below the 23 °C of average (Avila 20.6 °C, Valladolid 22.3 °C and Segovia 22.7 °C in July) and in the south are reached to exceed 26 °C (Real City 26.7 °C and Toledo 26.8 °C in July).
5. In the Guadalquivir valley are given the highest temperatures surpassing 28 °C (Bailén 29.9 °C, Seville 28.2 °C and Cordoba 28,0 °C in July). In the valleys of the Segura and Guadiana are surpassed 26 °C (Murcia 27.6 °C in August, Badajoz 26.1 °C in July).

Precipitation

Average annual rainfall in Spain

The estimated average annual precipitation over Spain in the reference period 1981-2010 is around 650 mm approximately. However, this average varies greatly from one place to another.

There are three types of rain:

• Convectives: originated by the vertical movements of the air, the warm air rises and enters into contact with cold air and creates clouds in a cottony way very related to the summer-end storms. They are stormy and happen in summer because it is when the cold air masses begin to enter the Iberian peninsula.
• Orographic: it is related to the Föhn effect.
• Frontals: They are the most common ones produced from contact with a hot air dough with another cold air, are associated with debris. They occur in autumn and winter.

The confluence of these precipitations explains the rainfall in the Iberian Peninsula. With the geographical factors we can cite some aspects that influence rainfall:

• Latitude: The Iberian peninsula is located at the southern end of the displacement of the polar front, precipitation will have a gradation that varies from north to south and from east to west, depending on where between the polar front. In the Peninsula there are two areas of influence, the Mediterranean and the Atlantic that explain the creation of the climate.
• Emplacement of the Iberian peninsula: it is within the general atmospheric circulation of the west and the drunks influence that it will rain more in the west than in the east.
• Peripheral relief: it produces that the wet air masses remain in the mountains and in the interior a certain degree of aridity is manifested.
• Relieve: rain or snow occurs from orographic rains.

Pluviometric domains:

Average annual precipitation map (mm) in Spain during the period 1981-2010.

1. Spain wet (over 800 mm/year): has no dry month. It extends to the north and northwest of the Iberian peninsula and to the large mountainous assemblies. The areas with the most precipitation are the Basque Country and Galicia. This is due to the Atlantic introduction and the incidence of the Föhn effect.
2. Spain semi-humid (between 600 and 800 mm/year): it is a wrap of the domain of the damp Spain and in medium-high mountains (montes de Toledo, Sierra Morena), is caused by the passage of cold fronts and associated Atlantic debris.
3. Dry Spain (less than 600 mm/year): it is given in the Ebro and Duero valley and much of the sub-meseta sur. Drought periods appear mainly in summer. Precipitations are given in winter and autumn and there are various behaviors in the rainy days, in the south subset rains less than in the north. Within this domain of precipitation stands out when there are less than 300 mm/year that is the arid Spain, which is located in certain areas the south of the Iberian peninsula such as Almeria, Murcia and areas to sotavento of the Cordillera Bética, areas of the Ebro valley and punctual spaces of Alicante and Albacete. The number of rainy days is around 40 and 70 days a year.

Köppen climate classification

The Köppen climate classification is a very common classification worldwide, using a combination of three letters. Capital letters are used for the first letter: "B" for dry climates, "C" for temperate climates, "D" for cold temperate (mountain) and "E" for cold climates with permanent ice (the tropical climate "A" does not occur in Spain). The second letter is written in upper case in the type "B" and can be "S" for the semi-arid climate or "W" for arid or desert climate. For the rest of the climates the second letter is written in lower case and in Spain only the types "s" for climates with dry summers and "f" for climates without a dry season. The third, which is always written in lower case, depends on the temperature. For dry climates (B) we write "h" when the average annual temperature is greater than 18 °C and "k" when it is less For the rest of the climates, we observe in Spain the subtypes "a" for hot-summer climates (average temperature of the hottest month greater than 22 °C), "b" for mild summer climates (mean temperature of the hottest month less than 22 °C but mean temperatures exceed 10 °C at least four months of the year) and c for subpolar climates (mean temperatures greater than 10 °C occur in less than four months a year). Finally, of the cold climates in Spain, only one of the two subtypes is observed: the ET tundra climate, characterized in that the mean temperature of the warmest month is between 0 and 10 °C. This climate occurs only in the higher altitude areas of the Pyrenees.

The description given below of the climate of Spain, based on the AEMET climate atlas, corresponds to the commonly used Köppen climate classification, with the only exception that it was chosen as the limit of the average temperature of the month most cold to separate temperate climates C and D by 0 °C and not -3 °C. This will result in D climates occurring to a greater extent (always in mountain areas) than if the usual criteria were used. In addition, as a consequence, the Csc Mediterranean subpolar climate will occur only in a small strip of Teide instead of, in addition, in certain mountainous areas of the peninsula; and the oceanic subpolar climate will not occur in Spain, although if the usual criteria were established it would occur in certain mountainous areas of the north of the peninsula.

In Spain, the most common climates are temperate type C, although dry climates (B) are also quite common, both in the Canary Islands and in a large part of the peninsula and the Balearic Islands. Type D cold temperate climates occur only in mountainous areas.

Mediterranean climate (Csa)

Monte de El Pardo, in Madrid, with a continental Mediterranean climate.

Embalse de Guadalest, in Alicante, Valencian Community, with Mediterranean climate.

This is the most common climate in Spain, occupying approximately 42% of the territory. It is characterized by having a dry and hot summer (average temperature of the warmest month above 22 °C). In the Iberian Peninsula it extends especially in most of the southern half, in the regions Mediterranean coasts, with the exception of the arid areas of the southeast, and in the lower altitude areas of the Northern Plateau. In the Balearic Islands it occurs throughout the island of Menorca, in most of Mallorca and in part of Ibiza. In the Canary Islands it occurs in areas of medium altitude of Tenerife, Gran Canaria and La Gomera and in coastal and medium altitude areas of La Palma.

The city of Malaga is a clear example of the Mediterranean climate (Csa):

Average observatory climate parameters of Malaga-Costa del Sol Airport (5 msnm) (reference period: 1981-2010, extremes: 1942-2016)
Month	Ene.	Feb.	Mar.	Open up.	May.	Jun.	Jul.	Ago.	Sep.	Oct.	Nov.	Dec.	Annual
Average temperature (°C)	16.8	17.7	19.6	21.4	24.3	28.1	30.5	30.8	28.2	24.1	20.1	17.5	23.3
Average temperature (°C)	12.1	12.9	14.7	16.3	19.3	23.0	25.5	26.0	23.5	19.5	15.7	13.2	18.5
Temp. medium (°C)	7.4	8.2	9.8	11.1	14.2	18.0	20.5	21.1	18.8	15.0	11.3	8.9	13.7
Total precipitation (mm)	68.7	60.2	51.6	43.6	20.3	5.5	0.4	6.0	20.2	57.1	100.5	99.6	533.7
Source: State Meteorology Agency

Mediterranean Oceanic Climate (Csb)

Landscape of Villaobispo de las Regueras, in León, with Mediterranean ocean climate.

This is the second most common climate in Spain, occurring in approximately 22% of the territory. Like the Mediterranean climate (Csa), it has a minimum of rainfall in summer but, unlike, summer is mild, since the average temperature does not exceed 22 °C in the hottest month. The most representative area of Spain with this climate is the south of Galicia. It is also found in mountainous areas of the Iberian Peninsula and Mallorca as a variation in altitude of the Mediterranean climate (Csa), as well as in the area of the Strait of Gibraltar. In the Canary Islands it occurs in inland areas, especially at medium-high altitude on the islands of Tenerife, Gran Canaria, La Gomera, El Hierro and La Palma.

The city of León is an example of the Mediterranean oceanic climate Csb:

Average climatic parameters of Observatorio del Aeropuerto de León (916 msnm) (reference period: 1981-2010)
Month	Ene.	Feb.	Mar.	Open up.	May.	Jun.	Jul.	Ago.	Sep.	Oct.	Nov.	Dec.	Annual
Average temperature (°C)	7.1	9.5	13.3	14.8	18.6	24.0	27.4	26.9	22.9	16.7	11.2	8.0	16.7
Average temperature (°C)	3.2	4.7	7.6	9.0	12.6	17.1	19.8	19.6	16.5	11.7	7.0	4.2	11.1
Temp. medium (°C)	-0.7	0.0	1.9	3.3	6.6	10.2	12.2	12.3	10.1	6.7	2.8	0.4	5.5
Total precipitation (mm)	50.0	34.5	32.0	44.8	56.3	30.7	19.4	22.8	38.9	61.1	59.1	65.6	515.2
Source: State Meteorology Agency

Another example of the Mediterranean oceanic climate Csb is the Tenerife North Airport observatory in San Cristóbal de La Laguna (Tenerife), although this is closer to the limit with the Mediterranean climate (Csa). In addition, unlike the climate of León, which has a moderately cold winter, it has a very mild winter:

Average weather parameters of Observatorio del Aeropuerto de Tenerife Norte (632 msnm) (Reference period: 1981-2010)
Month	Ene.	Feb.	Mar.	Open up.	May.	Jun.	Jul.	Ago.	Sep.	Oct.	Nov.	Dec.	Annual
Average temperature (°C)	16.0	16.7	18.2	18.5	20.1	22.2	24.7	25.7	24.9	22.5	19.6	17.1	20.5
Average temperature (°C)	13.1	13.4	14.5	14.7	16.1	18.1	20.2	21.2	20.7	18.9	16.5	14.3	16.8
Temp. medium (°C)	10.2	10.0	10.7	10.9	12.0	14.0	15.7	16.6	16.5	15.2	13.3	11.5	13.0
Total precipitation (mm)	79.9	70.2	61.4	38.8	18.7	10.7	6.4	5.2	15.9	47.0	81.1	82.3	520.3
Source: State Meteorology Agency

Oceanic Climate (Cfb)

Landscape of the town of Riotuerto, in Cantabria, with oceanic climate.

It is characterized by the constancy of rainfall throughout the year, without having a notable minimum of rainfall. Also, the warmest month does not exceed 22 °C. This climate occupies approximately 16% of the Spanish territory, being the third most common climate in Spain according to the Köppen climate classification. It occurs especially in most of the northern coastal strip (North Galicia, Asturias, Cantabria and the Basque Country, although it also occurs south of the Pyrenees in areas of medium altitude and in certain inland areas, especially in much of from the provinces of Burgos, La Rioja, Soria and Teruel, where the altitude moderates temperatures and prevents them from exceeding 22 °C on average in summer.

In the northern coastal strip, rainfall is very abundant, reaching more than 1500 mm per year. However, excessive rainfall does not always occur in the Cfb climate, as occurs in a large part of the province of Teruel where rainfall is between 400 and 500 mm per year. In coastal areas, temperatures in winter are softened by the sea (between 8 and 10 °C) and in summer they are mild (between 18 and 22 °C on average), with a very small temperature range. As we move further from the coast, winter gets colder. In inland areas that have a Cfb climate, it is the altitude that causes temperatures to not exceed 22 °C on average, which in turn causes average temperatures in January to be between 2 and 4 degrees.

The city of Santander, located on the Cantabrian coast, is an example of an oceanic climate (Cfb):

Average weather parameters of Santander Airport Observatory (5 msnm) (Reference period: 1981-2010)
Month	Ene.	Feb.	Mar.	Open up.	May.	Jun.	Jul.	Ago.	Sep.	Oct.	Nov.	Dec.	Annual
Average temperature (°C)	13.6	13.8	15.7	16.6	19.1	21.6	23.6	24.2	22.8	20.3	16.3	14.2	18.5
Average temperature (°C)	9.7	9.8	11.3	12.4	15.1	17.8	19.8	20.3	18.6	16.1	12.5	10.5	14.5
Temp. medium (°C)	5.8	5.7	7.0	8.3	11.1	13.9	16.0	16.4	14.4	11.8	8.7	6.7	10.5
Total precipitation (mm)	106.2	92.2	87.9	102.2	78.0	58.2	52.4	73.4	83.1	119.8	157.1	118.4	1129.0
Source: State Meteorology Agency

Humid subtropical climate (Cfa)

Santolea reservoir, in Teruel, Aragon, with humid subtropical climate.

This climate is characterized by constant rainfall throughout the year. However, unlike the oceanic climate (Cfb), summers are hot, exceeding 22 °C on average in the warmest month. This climate occupies between 3 and 4% of the Spanish territory and occurs almost exclusively in the low altitude areas of the Pre-Pyrenees and around the Ebro depression. In the areas where the Cfa climate occurs, rainfall is not usually too abundant., reaching almost the entire territory below 750 mm per year. In the surroundings of the Ebro depression, rainfall remains low, generally below 500 mm per year and falling below 400 mm in some areas, so that the climate remains close to the limit with the semi-arid climate, which occurs in most of the Ebro depression.

The city of Girona is an example of a humid subtropical climate Cfa:

Average weather parameters of Gerona Airport Observatory (143 msnm) (Reference period: 1981-2010)
Month	Ene.	Feb.	Mar.	Open up.	May.	Jun.	Jul.	Ago.	Sep.	Oct.	Nov.	Dec.	Annual
Average temperature (°C)	13.1	14.1	16.7	18.8	22.4	26.6	30.1	29.8	26.1	21.8	16.6	13.6	20.8
Average temperature (°C)	7.1	7.9	10.4	12.5	16.3	20.4	23.6	23.4	20.1	16.2	10.9	7.8	14.7
Temp. medium (°C)	1.1	1.7	4.1	6.2	10.1	14.3	17.1	17.0	14.1	10.5	5.2	2.0	8.6
Total precipitation (mm)	62.0	51.3	50.2	66.6	71.1	59.6	32.3	45.7	69.9	87.9	69.7	56.1	727.5
Source: State Meteorology Agency

Dry climates (B)

Alicante, in the Valencian Community, with semi-arid climate.

Cabo de Gata, in Almeria, Andalusia, with arid climate.

Type B climates are characterized by low rainfall. Two types are differentiated: the arid or desert climate (BW) that receives very little precipitation and the semi-arid climate (BS) in which the aridity is more moderate. Each of these two types is divided into subtypes warm (letter h) and cold (letter k) depending on whether the average annual temperature is higher or lower than 18 °C.

Semi-desert or semi-arid climate (BSk and BSh)

In the Iberian Peninsula, the cold semi-arid climate (BSk) extends widely over the southeast of the Peninsula and the Ebro valley and, to a lesser extent, in the southern plateau, Extremadura and the Balearic Islands, while the warm semi-arid climate (BSh) occurs only in small fringes of the provinces of Alicante, Murcia and Almería and, to a lesser extent, in Jaén and Seville. In the Canary Islands, arid and semi-arid climates are the most common. Specifically, the BS semi-arid climate is less common, although it occurs on practically all the islands, although it occurs rarely on Lanzarote, Fuerteventura and La Palma. In general, the warm semi-arid climate BSh occurs in coastal or low-lying areas of the islands while the cold semi-arid climate BSk occurs in higher-lying areas.

The city of Zaragoza is an example of the cold semi-arid climate (BSk):

Average weather parameters of Zaragoza Airport Observatory (263 msnm) (Reference period: 1981-2010)
Month	Ene.	Feb.	Mar.	Open up.	May.	Jun.	Jul.	Ago.	Sep.	Oct.	Nov.	Dec.	Annual
Average temperature (°C)	10.5	13.1	17.3	19.6	24.1	29.3	32.4	31.7	27.1	21.4	14.8	10.8	24.9
Average temperature (°C)	6.6	8.2	11.6	13.8	18.0	22.6	25.3	25.0	21.2	16.2	10.6	7.0	15.5
Temp. medium (°C)	2.7	3.3	5.8	7.9	11.8	15.8	18.3	18.3	15.2	11.0	6.3	3.2	10.0
Total precipitation (mm)	21.0	21.5	19.1	39.3	43.7	26.4	17.3	16.6	29.5	36.4	29.8	21.4	332.0
Source: State Meteorology Agency

Murcia is an example of the hot semi-arid climate (BSh):

Average weather parameters of Observatorio de Murcia (61 msnm) (Reference period: 1984-2010)
Month	Ene.	Feb.	Mar.	Open up.	May.	Jun.	Jul.	Ago.	Sep.	Oct.	Nov.	Dec.	Annual
Average temperature (°C)	16.6	18.4	20.9	23.3	26.6	31.0	34.0	34.2	30.4	25.6	20.3	17.2	24.9
Average temperature (°C)	10.6	12.2	14.3	16.5	20.0	24.2	27.2	27.6	24.2	19.8	14.6	11.5	18.6
Temp. medium (°C)	4.7	5.9	7.7	9.7	13.3	17.4	20.3	20.9	18.0	13.9	8.9	5.8	12.3
Total precipitation (mm)	27.1	26.8	29.5	25.0	28.2	18.1	2.9	8.1	31.7	36.4	32.1	28.6	296.6
Source: State Meteorology Agency

Desert or arid climate (BWh and BWk)

In the Iberian Peninsula, they are located in small areas of the southeast, in the provinces of Almería, Murcia and Alicante, coinciding with the minimum rainfall in the peninsula. Hot arid climate (BWh) occurs in low-lying or coastal areas while the less common cold-arid climate occurs in small mid-altitude areas. In the Canaries the hot desert climate (BWh) is the most common. It occurs practically on all the islands, especially in most of Lanzarote and Fuerteventura, in the south and coastal areas of Gran Canaria, in the south of Tenerife and in the coastal areas of La Gomera and El Hierro. The cold arid climate (BWk) is only observed in a testimonial way on the southwestern slopes of the islands of Tenerife and La Gomera, between 500 and 700 m altitude.

Most of Fuerteventura clearly has a hot desert climate (BWh), including Fuerteventura Airport as shown in the following table:

Average weather parameters of Fuerteventura Airport Observatory (25 msnm) (Reference period: 1981-2010)
Month	Ene.	Feb.	Mar.	Open up.	May.	Jun.	Jul.	Ago.	Sep.	Oct.	Nov.	Dec.	Annual
Average temperature (°C)	20.6	21.0	22.2	22.9	24.1	25.8	27.3	27.8	27.5	26.1	24.0	22.0	24.3
Average temperature (°C)	17.6	17.9	18.9	19.5	20.6	22.5	24.0	24.6	24.4	22.9	20.9	18.9	21.1
Temp. medium (°C)	14.7	14.8	15.5	16.0	17.1	19.1	20.8	21.5	21.2	19.8	17.7	15.9	17.8
Total precipitation (mm)	14.3	15.9	12.4	5.3	0.8	0.0	0.0	0.3	2.4	7.7	13.2	25.7	98.1
Source: State Meteorology Agency

Mountain climates (Dsb, Dsc, Dfb, Dfc, Csc, Cfc and ET)

Circus and summit of Peñalara, in Madrid, with mountain climate.

Spain has numerous high-altitude mountainous areas, which generates a very different climate from neighboring lower-elevation areas, mainly in terms of temperature, which drops the higher the altitude. The description of these climates is very complex since a few hundred meters of difference in altitude can trigger notable changes in the climate. Mountain climates can only be established from 1,000 m above sea level, distinguishing three floors or levels: subalpine (1,000-1,500 m), alpine (1,500-2,500 m) and snowy (>2,500 m).

According to the Köppen climatic classification we can distinguish several types of climate that occur in the numerous mountainous areas of Spain. The most common is the Mediterranean oceanic climate (Csb) already described above, which occurs, in addition to other low-altitude areas (generally in the north) or on plateaus, also in mountainous areas of medium altitude, normally below 2000 m. meters. The oceanic climate (Cfb) also occurs in low-altitude mountainous areas, generally in the north of the peninsula. Another very common type is type D cold temperate climates, which occur in higher altitude areas. These climates are characterized, in general, because the average temperature of the warmest month is above 10 °C and that of the coldest month is below -3 °C. However, as the AEMET does, we will establish 0 °C as the limit instead of -3 °C. This will mean that type D climates will occur to a much greater extent. Within the D climate we find the Df and Ds subtypes, the first characterized by the constancy of rainfall throughout the year and the second by having a minimum of rainfall in summer. The Df type occurs especially in the Pyrenees and also in a large part of the Iberian system. The Ds type occurs especially in the Cantabrian Mountains, in the Central System and in the Betic Cordilleras, as well as in other mountainous areas such as the Teide peak at altitudes higher than 2900 meters. The Df and Ds climates are subdivided into the Dfb and Dfc, and Dsb and Dsc types (the Dfa and Dfd climates, and Dsa and Dsd do not occur in Spain), where the letter b indicates that the average temperatures exceed 10 °C at least four months a year and the letter c indicates that the average temperatures above 10 °C occur in less than four months a year, registering in both cases an average temperature of the warmest month below 22 °C. Thus, the Dfb and Dsb climates occur in mountainous areas of medium-high altitude while the Dfc and Dsc climates occur in high-altitude mountainous areas. However, in the highest mountains of the Pyrenees, temperatures are very low, giving rise to the ET tundra climate, characterized in that the average temperature of the warmest month is between 0 and 10 °C. Finally, we find another type of very rare climate that is only observed in the Canary Islands, in a narrow strip around the Pico del Teide on the island of Tenerife, between approximately 2,600 and 2,900 m altitude: the so-called subpolar oceanic dry-summer climate. (Csc). They are characterized by an average temperature of the warmest month below 22 °C and because average temperatures above 10 °C occur in less than four months of the year; but, unlike type D climates, the average temperature of the coldest month is between 0 and 18 °C while that of the warmest month is above 10 °C. In addition, it has a minimum of rainfall in summer. However, if we considered -3 °C instead of the 0 °C average temperature of the coldest month, as is usually done, type D climates would occur to a much lesser extent, being restricted almost exclusively to the Pyrenees, Picos of Europe and Sierra Nevada, and occurring almost only the types Dsc and Dfc, to a much lesser extent the type Dfb and the type Dsb could occur only in Sierra Nevada in a residual way. In this way, the Csc climate would replace type D climates in various mountain areas of the Iberian Peninsula (mainly in the Cantabrian Mountains, Sierra Nevada, Central System and Montes de León) and in the Teide mountain from 2600 meters above sea level, except perhaps for the highest altitude area, with a Dsc climate. In addition, the oceanic subpolar climate (without dry season) Cfc would also occur in northern mountainous areas of the Iberian Peninsula (mainly in the Pyrenees, the Iberian System and in a small strip of northern Cantabrian Mountains). This climate differs from the Csc climate only in that rainfall is more or less constant throughout the year.

The Port of Navacerrada, in the Sierra de Guadarrama, has a Mediterranean hemiboreal climate Dsb if we establish the 0 °C average temperature of the coldest month as the limit between climates D and C and a Mediterranean oceanic climate Csb if we establish the - 3°C:

Average weather parameters of Navacerrada Port Observatory (1894 msnm) (Reference period: 1981-2010)
Month	Ene.	Feb.	Mar.	Open up.	May.	Jun.	Jul.	Ago.	Sep.	Oct.	Nov.	Dec.	Annual
Average temperature (°C)	2.3	3.0	5.8	7.0	11.5	18.0	22.4	22.2	17.2	10.6	5.6	3.3	10.7
Average temperature (°C)	-0.4	0.1	2.3	3.4	7.4	13.2	17.0	16.8	12.7	7.3	2.8	0.7	6.9
Temp. medium (°C)	-3.2	-2.9	-1.1	-0.3	3.2	8.3	11.5	11.5	8.2	3.9	0.1	-2.0	3.1
Total precipitation (mm)	123.8	95.9	83.8	127.1	124.5	63.5	23.2	26.0	60.2	155.7	176.4	163.1	1223.3
Source: State Meteorology Agency

The urban climate

Unlike other climates, the urban climate is a created climate: "the island of heat", from human intervention as a consequence of its activity in large cities: air pollution, big skyscrapers etc. This climate is considered a microclimate because of the size of the affected area, but not because of its repercussions, which in many cases affect the majority of the inhabitants of a region concentrated in one or several municipalities. No one can deny the interest of knowing the climatic conditions of the high mountains, the Iberian foothills or the plateau cereal-growing steppes, but most of us enjoy or suffer from the weather every day in an urban environment.

That the environment in big cities is deteriorating and is a cause for general concern is so obvious that it has even become part of political discourse. But, in fairness to the past, the burning red light should be more a warning about declining living standards than an intimidation for survival. Bad smells, noise, diseases of all kinds and the plague have been the inevitable waste of urban development since its origins. Dirt, crimes, overcrowding and catastrophes are the reverse of hygiene, respect for coexistence and quality of life achieved from an urban culture.

References to the unsanitary conditions of cities already appear in classical texts, but it was only from the XIX century that they establish scientific criteria to evaluate the effects of pollution on the urban climate. Howard, in his book on the climate of London deduced from meteorological observations (1818) links the fog (fog city) with the emission of pollutants by combustion and highlights, for the first time, the thermal contrasts between the city and the countryside. But it is Chandler (1967) who writes, also about London, the first rigorous study on urban climatology.

We said that since its origins the city has always had different physical living conditions, a different climate from the rural environment. But it is from industrialization when the contrasts have sharpened to the point of being perfectly measurable in the following aspects: fog, humidity, winds, rainfall and temperatures.

• The urban fog It is not only a horizon of droplets of water in suspension that reduces visibility but it is a decisive part of other contaminants such as smoke, hollines, harmful aerosols, various gases, etc. There can even be fog without humidity and then it receives the name of smog (humo and fog), now internationally accepted word as synonymous with thick and highly contaminated atmosphere. This is frequent in the big cities during the winter, with the wind in calm and under the control of the anticyclone. The effects on those with respiratory ailments can be lethal, as happened in the emblematic London case (5-9 December 1952), during which nearly 5000 people died because of the smog. Since then, rigorous measures have been taken in the emission of pollutants to the atmosphere: by removing numerous industries from the urban centre, by decree reducing the schedule of heating or regulating the circulation of cars by pairs and odd tuition according to the days. The expansion of pedestrian areas in historical cases is one more example of this environmental concern.

Madrid and Barajas are a good example of the influence of the urban area in the formation of fog: the city registers 38 days per year and the airport 17. The five days of fog in Valencia, at the beginning of the century, have become 16 in recent decades, undoubtedly due to its strong industrialization.

In summary, and with respect to the rural environment, the urban area suffers 100% more fog in winter and 30% in summer.

• Humidity. It seems that there are still no conclusive studies on the values of relative humidity in the city and its surroundings. According to Sukopp (1989) this is 2% wet in winter and 8-10% in summer. The causes must be sought in the absence within the urban perimeter of large masses of water and vegetation, despite the large volumes of steam provided by the heating and combustion by traffic, as water is a by-product of hydrocarbons.

• The speed of the wind in the city is between 10-20% weaker than in the field due to the constant friction with the buildings and the interposition in its path of perpendicular streets. It is also true that, on some occasions, the wind can acquire greater speed if it is lined by a long and narrow way. As a general rule, the strong winds are faster in the countryside and the weak (3-5 m/s) gain speed within the urban hull. In this is a phenomenon that, on a small scale, reminds us of the famous equatorial chimney: from the center there is a convective current that when cooling down descends by both extrarrads.

A wind exchange similar to that between the sea and the coast is also established with the countryside: during the day the breeze flows from the city to the outside, warmer due to the greater amount of radiation received, and during the night the phenomenon is reversed as the countryside cools faster than the city.

• Urban precipitation they are more quantitative than rural ones in 5-10%, reaching up to 30%. According to López Gómez it is possible that the greatest thermal and mechanical turbulence is more effective than contamination (1993:27) in attracting rainfall on the urban centre. Among the causes of this phenomenon are:
• The upward convective currents originated on the heat island.
• The presence of numerous condensing cores that feed the formation of fog and clouds.
• The contribution of abundant water vapor by heating and industrial uses.

As a summary, it has been verified here and in other countries that large cities receive more precipitation than their surroundings, that they enjoy more rainy days, that summer storms (some accompanied by hail) are somewhat more frequent and that, on the contrary, the snow makes less of an appearance due to the heat that envelops the city like a noxious protective mushroom.

• Annual temperature of the city is somewhat higher (1-3°) than extramuros, but this value is not relevant. True differences are established during the night: 4-6° are common and have been recorded up to 11°. The center has received the name of heat island (or artificial oasis) because as such it behaves. Many factors contribute to the development of this phenomenon:

• The city, due to the rooting of its atmosphere, receives less radiation than the countryside, but this same contaminated layer behaves like a protective coil and prevents during the night that heat escapes.

• Throughout the day the buildings and streets are enticing heat that radiate during the night, a non-existent phenomenon in the countryside.

The interior of cities such as Madrid (in the image) has a microclimate due mainly to the barrier that forms its buildings in front of the atmospheric agents.

• When it rains the water stays long on the urban surfaces because it is waterproof mostly. By rapidly disappearing by sinks, a very small part of the liquid is susceptible to evaporation, a process in which the atmosphere consumes 600 calories per gram, which would lead to an important cooling of the environment.

The heat island reaches its maximum development with anticyclonic weather and calm winds. If it blows or the rain-laden cyclone arrives, both erase the contours of the former.

Finally, the presence of a prominent relief or a wide river breaks the continuity of the heat island downwards, in the same way that large buildings positively increase its curvature, hence the thermal zenith is identified with the denser core and tapers towards the periphery.

In addition to all the concrete repercussions on the quality of life of citizens, the intensification of the "heat island" is increasingly affecting Weather Stations, which are being "locked up" in this heat island, not reflecting the regional climate, but only the urban one. There are mathematical procedures that could help remove the drift due to "urban heat" from temperature values.