In meteorology and climatology the term sunstroke has two meanings. On the one hand, it refers to the number of hours that the Sun illuminates a point on the Earth’s surface, or, more precisely, the number of hours that it illuminates it directly, that is, shining on the horizon. On the other hand, it defines incident solar radiation, that is, the amount of short-wave solar radiation that reaches the earth’s surface. Solar radiation incident on the earth’s surface is of two types: direct radiation and diffuse radiation. Direct radiation is that which comes directly from the solar disk, when the day star is seen. On a day with clouds, which hide the sun, radiation also reaches us, but it is diffuse radiation.
Insolation, with its appreciable annual cycle at the latitude in which Andorra is located, constitutes the component that most characterizes the climate dynamics of our country, because it directly conditions the annual temperature cycle, and therefore allows us to speak of winter and summer, with clear features, not even blurred on a meteorological scale, that is, not even diluted to a short temporal limitation.
In the article that we present below, we will, from a climate point of view, do a brief quantitative analysis of the subject of insolation in Andorra, based on the data provided by the National Meteorological Service relating to both what the Andorran Government’s meteorological website, meteo.ad, considers as insolation, the number of minutes or hours of sunshine, and what corresponds to incident solar radiation. To do this, we will fundamentally use the values taken from the meteorological station of the Roc de Sant Pere, a station that is located at 1,135 m altitude in the sunny part of the central valley of our country and which has the longest series of data on the parameters in question. As a complement, we will present incident solar radiation data corresponding to two other meteorological stations in the country such as Aixàs and El bony de les Neres. Aixàs is located in the southern part of Andorra at an altitude of 1,538 m and the Bony de les Neres, in the central sector of the Andorran territory at 2,080 m. These two complementary stations, although they do not offer sufficiently long data series, allow, in any case, to infer or project some approximate climatic conclusion of the place where they are located.
Regarding annual insolation, and in the basic period 1992-2025, the rock of Sant Pere has an average of 2,079 hours of sunshine per year. It is a moderate insolation, although it must be borne in mind that the rock of Sant Pere corresponds, in fact, to a sector of the bottom of the valley, where the shadow effect produced by the relief is pronounced, and we all know this in a country with an orography as rugged and rugged as Andorra.
It directly conditions the annual temperature cycle
To give us a comparative idea of the rock of Sant Pere with the extreme values recorded in peninsular Spain, we will point out that the average annual maximum of hours of sunshine corresponds, in this peninsular Spain, to the coastal area of the Gulf of Cadiz or the area of Almeria, where there are a little more than 3,000 hours of sunshine per year (thirty years 1991-2020), while the minimum is located in the Cantabrian strip; specifically, Bilbao receives only about 1,700 hours of sunshine per year on average, also in this thirty-year period 1991-2020.
The maximum average monthly insolation of the Roc de Sant Pere, also in the basic period 1992-2025, is July, with 250.3 hours, and the minimum average monthly is December, with 100.0 hours. Although June is the month with the most hours of daylight, the insolation in this sixth month of the year is lower than that of July, even lower than in August, and this is basically due to the fact that the cloudiness is more prominent in June, which slows down the insolation. In July and August, anticyclonic conditions with many hours of clear skies are more common, even predominant, as befits the summer season. Also worth noting is the fact that the number of hours of sunshine is slightly lower in April, at 166.9 hours, than in March, at 176.2 hours, even though the day is shorter in this month. In fact, as we all know, in April the weather is usually more variable than in March with more clouds.
In terms of incident solar radiation, the Sant Pere rock has an average annual record, in the same basic period 1992-2025, of 5,211,291 megajoules per square meter (MJ/m2; 1 megajoule = 1,000,000 joules). El bony de les Neres, for the basic period 2015-2025, and Aixàs, for the basic period 2016-2025, present an average annual incident solar radiation of 5,550.113 and 5,536.335 MJ/m2, respectively. These Andorran values are lower than those that occur, as peninsular maximum values, in the arid Mediterranean climate region of the Iberian Peninsula, especially Murcia and Almeria, where it reaches approximately, on average, 7,560 MJ/m2 per year, and exceed those of the northern coast of Galicia and those of the higher areas of the Cantabrian mountain range, which constitute the Iberian peninsular minimum, with less than 4,000 MJ/m2 annual average.
In the Andorran Pyrenees, the month with the highest amount of incident solar energy is July, and the month with the lowest, December. The Roc de Sant Pere station presents, in the basic period 1992-2025, a record of 704,781 MJ/m2 of solar energy received on average in July, while in December this station in the parish of Andorra la Vella receives an average amount of 158,213 MJ/m2.
In this way, and as a conclusion, we can see that, despite not reaching the values of many other even sunnier sectors of the Iberian Peninsula, insolation, in Andorra, is, both from the point of view of the duration of the hours of sunshine and the amount of solar radiation received, an important resource, to which the transparency of the Andorran air contributes, a transparency favored by the altitude, and the practical absence of the mists, due to the fact that they are found, the Valira valleys, in a fairly continentalized area of the southern Pyrenean slope. This, even, if we take into account the appreciable annual cycle of insolation in our Pyrenean country, with significant differences between winter and summer. This relevance that the Sun King has in our house is already taken into account in terms of its use in the various facets of recreational, economic or productive activity.
