Climate and Weather Factors in Spain and the Canary Islands
Climate Factors
Climate factors are those aspects that influence permanent and unchanging climate.
1. Geographical Factors
These include latitude, location, configuration, currents, and relief:
a) Latitude
Spain’s latitude, in the Northern Hemisphere’s temperate zone, determines the existence of two distinct seasons: summer and winter, separated by two transitional seasons, spring and autumn. In the Canary Islands, due to their location south of the temperate zone and proximity to the intertropical domain, the contrasts between seasons are less marked.
b) Location
The Iberian Peninsula’s location between two seas with different thermal characteristics (the Atlantic and the Mediterranean) and between two continents (Europe and Africa) makes it a crossroads of different air masses. The Canary Islands, due to their proximity to the African coast, also receive various atmospheric influences.
c) Configuration
The solid configuration of the peninsula, due to its large width, allows us to distinguish between a periphery open to the influence of the Atlantic or the Mediterranean and a wide inland core, isolated from marine influences and with a clear continental trend.
d) The Gulf Stream
Originating in the Gulf of Mexico, the Gulf Stream flows SW-NE, affecting the Galician coast by providing it with warm water. However, west of these coasts, a branch breaks off, following a southerly direction and reaching the Canary Islands. As it descends, it progressively encounters warmer waters, so that upon reaching the archipelago, it has lower temperatures than the rest of the body of water at those latitudes. Thus, it becomes a current known as the Canary Current, which increases the stability of the air in summer.
e) Relief
Relief influences climate through its orientation and height.
The orientation of the relief is mainly peninsular (W-E), except in the Iberian System. This facilitates the entry of maritime air masses from the west, but the massive character of the Peninsula makes its activity decrease as it penetrates inland, causing the air masses to lose much of their moisture and increase their temperature. Conversely, this arrangement hinders the passage of meridian air masses (N-S) inland.
Relief also determines orographic precipitation. When an air mass encounters a mountain barrier, it is forced to ascend. The water vapor it contains cools and condenses, producing rainfall on the windward side of the mountain (the side facing the ascending air). After the summit, the air descends and warms, producing a dry leeward side of the mountain (the side facing the descending air). In the Canary Islands, the windward slopes are exposed to the constant trade winds and experience significantly higher precipitation than the lowlands.
2. Thermodynamic Factors
These factors are responsible for atmospheric circulation, which determines both weather and climate. Atmospheric circulation is driven by the jet stream at high altitudes and by action centers, air masses, and fronts at the surface.
a) Circulation at High Altitudes
In the temperate zone, circulation at high altitudes is headed by the jet stream. This is a strong, tubular-shaped wind current that flows between 9 and 11 km in height. It mainly affects Spain in winter, as it moves to more northern latitudes in summer.
The jet stream is responsible for weather patterns on the surface. When it flows quickly (over 150 km/h), it has a nearly zonal path (W-E). However, when it slows down, it forms waves: ridges of high pressure and troughs of low pressure, which are reflected on the surface and give rise to dynamic anticyclones and depressions.
b) Surface Circulation
Surface circulation is driven by action centers, air masses, and fronts.
* Action Centers
Action centers are areas of high and low pressure. A high-pressure area, or anticyclone, is an area of higher pressure than normal (1016 mb) surrounded by areas of lower pressure. Winds circulate around it clockwise. It produces stable weather. A low-pressure area, or depression, is an area of lower pressure than normal surrounded by areas of higher pressure. Winds circulate counterclockwise around it. It produces unstable, often rainy weather.
According to their origin, action centers can be thermal or dynamic:
- Thermal anticyclones are formed when an air mass cools. Cold air is denser and exerts high pressure as it descends. A thermal low forms when the air is heated; it becomes less dense, rises, and exerts low pressure.
- Dynamic action centers are formed in certain areas where the jet stream forms ridges (anticyclonic areas) or troughs (depressionary areas) at high altitudes, which are reflected on the surface.
The action centers that direct atmospheric circulation on the Iberian Peninsula and the Balearic Islands are:
The anticyclonic action centers are the Azores anticyclone, which moves north in summer and south in winter; the Atlantic polar anticyclones; the European continental thermal anticyclone; and the thermal anticyclone inside the peninsula.
The depressionary action centers are the Iceland depression, the Gulf of Genoa depression, and the thermal depressions in North Africa and the interior of the peninsula.
In the Canary Islands, the main action center is the Azores anticyclone. When it moves, it can allow the passage of storms from the temperate zone and Saharan air from Africa.
* Air Masses
The atmosphere is divided into air masses, which are bodies of air with specific characteristics of temperature, humidity, and pressure that they acquire in their source regions.
Due to Spain’s latitude, the source regions of the air masses that affect it are: the cold Arctic (A) or polar (P) areas and the tropics (T), leading to cold or warm air masses, respectively. In both cases, depending on the surface of the source region, they can be maritime air masses (m) – humid – or continental air masses (c) – dry. These original characteristics can be modified if the air masses travel long distances.
* Fronts
When two air masses with different characteristics come into contact, they do not mix but are separated by a zone called a front, along which there is an abrupt change in air properties.
The most important front for Spain is the Polar Front, which separates tropical and polar air masses. The undulations it experiences give rise to storms associated with two fronts, which cause precipitation.
Weather Elements
To determine the weather, observations of atmospheric conditions must be made over time. These observable and measurable aspects of the air are the elements of weather. The main ones are:
a) Sunshine and Cloud Cover
Insolation is the amount of solar radiation received by a surface. Spain, due to its latitude, receives a large amount of solar energy, the highest in summer (long days) and the lowest in winter. Minimum cloud cover occurs in summer and maximum in winter.
b) Air Temperature
Temperature is the degree of heat of the air. It is milder near the sea and decreases inland, northward, and with altitude.
Highlights of temperatures in relation to climate are:
- The annual temperature range is the difference in temperature between the warmest and the coldest months. The ranges are lowest in the Canary Islands and along the coast, especially in northern regions.
- Frosts occur when air temperatures fall below 0°C. They can be radiation frosts (caused by ground cooling) or advection frosts (caused by the arrival of a cold air mass). The fewest frosts occur on the coasts, due to the moderating influence of the sea on temperatures.
c) Humidity
Humidity is the amount of water vapor the air contains, derived from evaporation. It decreases with increasing temperature, being lowest in summer and highest in winter. Fog occurs when moisture in the air condenses in the bottom layer of the atmosphere.
Haze is a type of fog that occurs in the lower layers of the atmosphere due to the presence of dust particles. It forms in Spain during the summer in dry anticyclonic situations when soils are dry and fine particles can be lifted and kept in suspension by upward movements caused by strong ground heating.
d) Pressure and Wind
Atmospheric pressure is the weight of the air above a unit area. On the Iberian Peninsula, high pressures (associated with cold air) dominate in winter, while low pressures dominate in autumn and spring, and high pressures return in summer, although there are thermal lows inland (rising air due to ground heating). The Canary Islands are dominated by tropical high pressure (the Azores anticyclone), which, when it moves south in winter, can give way to Atlantic storms.
Winds are caused by pressure differences, flowing from high to low pressure. The peninsula, due to its latitude, is in the zone of westerly winds. There are also various local winds. The Canary Islands are dominated by the trade winds, which have a NE-SW component that originates on the eastern edge of the Azores anticyclone. Due to their origin, they are cool and humid, resulting in mild temperatures in both winter and summer.
e) Precipitation
Precipitation is the water that falls from clouds, either in liquid or solid form (snow, sleet). It increases with altitude and on windward slopes. It is also higher in the western half of the peninsula because the fronts coming from the west lose intensity as they move eastward.
f) Evaporation, Evapotranspiration, and Aridity
- Evaporation (the physical change from liquid to vapor at ambient temperature) is mainly favored by high temperatures, so it is higher in summer and at midday.
- Evapotranspiration also measures the water evaporated by transpiration from plants and soil.
- Aridity (how heat and humidity relate in a given area) increases with temperature and low rainfall.