Climatology
Jean-Michel Fallot, Institute of geography and sustainability, FGSE
The region of the Valais Alps, which corresponds to the canton of Valais, spans an area of 5,224.25 km², with altitudes ranging from 372 meters (Lake Geneva) to 4,634 meters (Pointe Dufour in the Monte Rosa massif). With the exception of the Lower Valais, which is exposed to humid airflows from the West and North, the rest of the canton is shielded from these airflows by the Bernese Alps, as well as from the Southwest to Southeast by the main ridge of the Valais Alps. As a result, the central and Upper Valais enjoy a much drier and sunnier climate compared to the rest of Switzerland, with only Ticino experiencing a similar level of sunshine.
Average annual temperatures measured from 1981 to 2010 are approximately 10 to 11°C in the Rhône plain, the Chablais, and central Valais, 2 to 3°C at 2,000 meters above sea level, and -3°C to -4°C at 3,000 meters. Monthly average temperatures range from 0 to 1°C during the coldest month (January) to 19 to 21°C during the warmest month (July) in the Rhône plain downstream from Leuk. At high altitudes of 3,000 meters, temperatures range between -10°C and +4°C. Snow and glaciers are present year-round on the highest peaks of the Valais Alps. The valley floors can foster cold air accumulations that influence average temperatures, especially during the cold season, notably in the Conches and Lötschental valleys.
Precipitation also varies significantly based on regional and local topography in the Valais Alps. On average, 550 mm of precipitation falls annually in the driest location in the Valais and Switzerland at Ackersand-Stalden, 600 to 800 mm in the Rhône valley between Martigny and Brig, as well as in the side valleys of the Valais Alps, and 1,000 to 1,200 mm in the Rhône valley in Lower Valais. Precipitation exceeds 2,000 mm annually on the peaks of the Chablais Pre-Alps and the main ridge of the Valais Alps (Grand St-Bernard) and even reaches 3,000 mm per year on the highest summits of the Bernese Alps.
The precipitation regime is semi-continental, with generally higher precipitation during the warmer season (thunderstorms) in the Chablais and the northern slopes of the Alps. However, this summer precipitation maximum is much less pronounced in Valais above St-Maurice, where a more or less marked winter precipitation maximum appears, similar to the Jura regions of Neuchâtel and Vaud. This indicates the influence of the oceanic climate, which diminishes as one moves eastward and into the Upper Valais. Near the main ridge of the Valais Alps and in the Simplon region, the regime changes significantly, with two precipitation maxima in spring and autumn, corresponding to a higher frequency of humid airflows from the Southwest to Southeast, originating from the Mediterranean. These create a blocking effect on the southern slopes of the Alps and the main ridge of the Valais Alps, resembling the characteristics of a north Mediterranean climate, similar to Northern Italy and Ticino.
