Donnas extends on the south-eastern part of Aosta Valley and its territory was formed during the Quaternary period by the movement of the Balteo glacier, which gave shape to the basin of the Dora Baltea. Donnas in on the borderline with the Municipalities of Aosta Valley: Arnad, Bard, Perloz, Pont-Saint-Martin, Pontboset and Hône and with Piedmont, in particular with Chiusella Valley and Quincinetto. Its surface area is 34,24 Km2, whose 3/4 are on the orographic right side of the Dora Baltea. The valley bottom represents 10% of the surface, while the steep sides 90%.
Donnas is well-known for its particular microclimate, mild and dry. It is possible to admire on the territory some tree species, which are not typical of our latitudes, such as the Maritime Pine wich has been growing up for more than 120 years in front of the parish Church. Furthermore, it has to be remembered that agaves grow on the hill of Adret and some palm trees in the gardens of the Centre, facing the Dora.
The mildness of climate is remembered in the Tsanson dou Pay, published on the “Messager Valdôtain” in 1929: “[…] A Donnas l’y at pà d’iver! / L’an pà gneun le tsaousson deper.” (At Donnas winter does not exist / nobody wears odd socks).
The notes explain the meaning: “Donnas est appelé la Nice de la Vallée d’Aoste. A cause de son climat si doux, les gens y sont la plupart du temps déchaux: ainsi, ils ne peuvent pas avoir les bas dépareillés” (Donnas is called the Nice of Aosta Valley. Thanks to its mild climate people goes almost always barefoot, so they cannot have odd socks).
The two sides, Adret and Envers, are really different from one another particularly in the winter. In fact, at the Envers ice lasts for a long time because the sun, hidden by the mountains, has been lacking for about three months a year, both at the valley bottom and high.
It is possible to check weather forecast on real time on the website of the Autonomous Region of Aosta Valley, as data have been recorded by the Clapey Station at the Envers at 314 AMSL since 1994.
The official height of the Municipality is written on a marble plate at the railway station: 320 meters. The Bec Renon, on the orographic right side, marks the highest altitude. It is a peak which declines until the plane and marks the entrance door of Aosta Valley. From this altitude it goes at Bec delle Strie (2.544 m.) and at Mont Debat (2.622 m.), peak overlooking both Mouilla Valley and Retempio Valley in the Municipality of Pontboset.
The left side is particularly steep and it goes uphill to Tête de Cou (1.410 m.) and Croix Courma (1.958 m.), where the borders of Donnas, Perloz and Arnad join each other.
The area of the hill country houses of the Envers (Praposa, Pianah, Pianfey, Chanton) has been clearly shaped by the glaciers and it ends with steep sides created by the river and the plain of Albard at the Adret. The hamlet of Montey is a particular area built on an alluvial conoid formed by the detritus brought there by a lateral stream. Also the steep hill of Rovarey has been formed over time by detritus brought by the stream Bellet from Croix Courma to the bottom.
The Dora Baltea travels on the valley bottom. It is the longest and most plentiful river of the western Alps, having its origins at the foot of Mont Blanc where the Val Veny and Val Ferret streams join.
The Dora Baltea, with its affluents Fer, Valbona, Valsorda and Boretta (right orographic side) and the streams Bellet and Legnan (left orographic side), has always been a part of the history of Donnas, also for reasons connected to hard times. Several are the hydrogeological events which have marked both people and territory, starting from the flood of the Dora on June 1620 to the “Débacle” of Bellet in 1831, from the landslide between Donnas and Pont-Saint-Martin in 1855 to the rocks carried by the Legnan stream which destroyed the vineyards in 1868, from the landslide of Montey in 1910 to the Fer flood in 1987, until the flood in 2000.
Other streams on the orographic left side are the Valley Goyet, whose source in at Albard, the Valley Alban and the Valley de Palcet, today completely dried, but with a certain flow rate in the past, as witnessed by the old banks wich are still at Ronc-de-Vaccaz.
In olden times then, as written by P. L. Vescoz “ (the Hellex, the current Lys) au sortir des gorges de Perloz, et à une petite distance du pont romain, il jetait vers le couchant une branche qui allait se joindre avec les eaux de la Doire près de Ronc de Vacca.” (The Lys, coming out from the canyon of Perloz, not far from the Roman bridge, soared a stream westward reaching the Dora river nearby Ronc-de-Vaccaz).
In the territory of Donnas there is also a lake in a basin uphill the hill country house of Liet at 1673 meters high. The partially flat banks, but with a lot of stones scattered all over, are a pasturage area.