56 Port anD the Douro
CliMate: MaCro, Meso, MiCro
The weather conditions in the north of Portugal bear a remarkable similarity to the wine
country of northern California. This is explained by their proximity to a large expanse
of cold ocean, the Atlantic and Pacific respectively. During the height of summer, the
waters of the north Atlantic are still so cold that they cause a bank of fog to build up
just offshore. It lurks there after sunset and rolls in silently during the night, frequently
leaving Oporto shrouded in fog at daybreak. Occasionally it will cover the entire litoral
of northern Portugal, gradually burning off progressively towards the coast as the sun
penetrates. Mark Twain’s observation ‘the coldest winter I have ever spent was a summer
in San Francisco’ might apply equally to Oporto.
In winter, spring and autumn Atlantic depressions bring rain-bearing westerlies
causing frequent heavy downpours on the hills and mountains that rise from the narrow
litoral. Oporto, by no means the wettest place in northern Portugal, receives an average
of 1,200mm of rain a year. By way of a comparison, the annual rainfall in Manchester,
north-west England (the butt of many a wet joke), amounts to 800mm. It is therefore no
coincidence that the coast north of Oporto is known as the Costa Verde (Green Coast)
and the local wine is the distinctly cool climate, high acid/low alcohol Vinho Verde.
Although the Vinho Verde region abuts the Port and Douro demarcation, no two
wines could be more different. Surrounded on three sides by high mountains, the upper
reaches of the Douro are largely protected from the Atlantic, earning it the provincial
name of Trás-os-Montes (‘Behind the Mountains’). To the north the Serras de Alvão,
Padrela and Bornes help to shield the region from cold northerlies. Directly to the west
the granite massif of the Serra do Marão, rising to 1,400 metres, casts a rain shadow
over the entire region. Along the entire length of the Douro Valley there is a steady but
dramatic transition from the temperate, humid Atlantic conditions that prevail on the
coast towards the more extreme continental climate of the central Iberian meseta. It is not
uncommon to leave Oporto shrouded in grey mist, traverse the Marão in a downpour
and emerge on the other side in bright sunshine.
At a mesoclimatic level the transition is evident within the 90-kilometre extent of the
Port wine region itself. This is most clearly illustrated by the annual rainfall figures along
the course of the River Douro. Lying immediately to the east of the Serra do Marão at
an altitude of 430 metres, Vila Real (the regional capital of Trás-os-Montes) receives an
average of 1,130mm. Down by the river at an altitude of roughly 100 metres, the annual
average rainfall at Régua is around 950mm. This figure drops to 650mm at Pinhão in the
heart of the Port wine region, 25 kilometres upstream. By the time you reach Barca d’Alva
another 70 kilometres upstream on the frontier with Spain, the average annual rainfall
total is as little as 380mm a year.
Rainfall in the Douro is strongly seasonal, with heavy rains in the winter and spring
sometimes giving way to long periods of unrelenting drought during the summer
months broken only by occasional localised thunderstorms. During the wettest months
(December and January, March in some areas), average monthly rainfall varies from over