Po Valley

• 1. The Po Valley

  ›

  The Po Valley, known in Italian as the Pianura Padana, runs about 650 km from the Western Alps to the Adriatic Sea. It is also called the Po Plain, the Plain of the Po, and the Val Padana. Its area covers roughly 46000 square kilometres, and about 17 million people live on it, a third of Italy's population.

  The river that gives the valley its name starts at about 2100 m, in the southern Piedmont province of Cuneo, nicknamed the Provincia granda. It finishes in the delta country of the Polesine, around Ferrara, where the ground lies about 4 m below sea level. Count the flatlands of Veneto and Friuli, and the whole thing becomes the largest plain in Southern Europe.

  How did such a vast, flat floor come to exist? Why do so many people crowd along a narrow band of springs rather than beside the river itself? And why does a place this productive now sit near the top of European lists for dirty air?

  12323

• 2. Buried Canyons

  ›

  Between 7 and 5 million years ago, in a span geologists call the Messinian, a long filling began beneath northern Italy. Under the plain lies a foreland basin and a system of deeply buried ancient canyons. They survive from a collision between an offshore land mass named Tyrrhenis and the mainland, one episode in the larger collision of the African and Eurasian plates.

  Sediment has been pouring into those canyons ever since. Most of it comes from the older Apennines, with a smaller share from the Alps. Some geologists describe the result as a syncline, a dip in the crust caused by compression at the edges. Whether or not that label fits, the valley is plainly a trough packed with sediment and continuous with the deeps of the Adriatic.

  The surface therefore has two kinds of landform. One is the flat fill itself. The other is the hilly country along the margins, where original rock shows and fans of outwash spread out from the Apennines and the Alps.

  Until about 1950, the Po delta kept growing outward into the Adriatic. The shoreline depends on a balance between the rate of sedimentation and isostatic factors, which are slow adjustments of the crust. After 1950, human interference with factors such as sedimentation turned growth into retreat. The delta began to degrade and the coast began to sink, feeding a continuing crisis in the city of Venice.

  Deep rock holds resources as well. The Malossa gas condensate field, found in 1973, produces from a depth of 6 km. Its reservoirs are dolomite from the Upper Triassic and the Lower Jurassic, sealed beneath a Lower Cretaceous marl known as the Marne di Bruntino.

  6516

• 3. Rivers and Borders

  ›

  In 1989, Italy passed Law no. 183/89, creating the Po Basin Water Board. Its task is to oversee the protection of lands, the rehabilitation of water, and the management of hydro resources across the basin. The law defines that basin as the territory where rain, snowmelt and glacier melt run over the surface and gather into streams, either directly or through tributaries.

  Drawing a boundary around the valley depends on who holds the pen. The board's authority reaches into several northern regions. It includes the plain north of the Adriatic and the territory south of the lower Po. The United Nations Environment Program draws a tighter line. It takes in the Alps and Apennines as far as the sources of the Po's tributaries, but it leaves out Veneto and the part of Emilia-Romagna south of the lower river.

  The flatlands of Veneto and Friuli explain part of the confusion. They do not drain into the Po, yet they join the Po plain into one unbroken surface. Many other streams cross this ground straight to the sea. The Savio, Lamone and Reno lie to the south. The Adige, Brenta, Piave and Tagliamento cross the Venetian Plain to the north. All of them empty into the northern Adriatic.

  The Po proper collects water from both sides. From the Apennines in the south come the Tanaro, Scrivia, Trebbia, Panaro and Secchia. From the Alps in the north come the Dora Riparia, Dora Baltea, Sesia and Lambro, along with four rivers tied to great lakes. The Ticino drains Lake Maggiore, the Adda drains Lake Como, and the Oglio drains Lake Iseo. The Mincio drains Lake Garda and carries the name Sarca in its upper reaches.

  21323

• 4. The Line of Springs

  ›

  In Piedmont, the dry upper plain goes by names such as vaude and baragge, while Lombardy uses brughiere and Groane. Each name hints at ground that is only modestly suited to farming. Beyond the valley proper, the Friulian magredi describes the same kind of country, far from reachable water tables and covered by dense woods or dry soil.

  Below this drier zone lies the lower plain, which is very fertile and well irrigated. In Lombardy and western Emilia it is called la Bassa, meaning the low plain. The name comes from a geologic feature called the fontanili line, a band of springs that runs mostly along the north, at the foot of the mountain slopes. It ranges from a few kilometres to as much as 50 km in width.

  The springs exist because the rock above the line is porous. Water in the mountains' intermittent streams sinks underground, then rises again where the water table meets the surface. This belt is often called the middle valley.

  The rivers themselves are a poor source of drinking water. Their flow is unreliable and often destructive, and sewage and fertilizers pollute it heavily. Their main uses are hydroelectric power, irrigation, and shipping for industry. Purifying river water for people to drink would cost too much.

  So the valley drinks from hundreds of thousands of wells, concentrated in the spring zone. Major settlements grew up there for the same reason, and it became the centre of Italian industry and economic development. Today that belt forms an almost continuous megalopolis from Turin to Trieste.

  783

• 5. Draining the Swamps

  ›

  The lower plain was settled and farmed earlier than any other part of the valley, in Etruscan and Roman times. After the Roman Empire collapsed in the 5th century AD, nobody kept up the irrigation works. A cooling climate phase, called the Migration Period or the Dark Age Cold Period, made matters worse. The valley slowly filled with standing water, and natural depressions on the right side of the Po became vast swamp basins.

  This waterlogging continued until the 10th century and shaped how people lived. Historical and archaeological evidence shows that they fished the wetlands and travelled across them by boat. Early medieval sites sat on fluvial ridges, which stood higher than the surrounding swampy meadows and offered strategic positions.

  By the 8th and 9th centuries, large landholdings were taking shape, and they sped up reclamation and heavier use of the land. Documents from the late 8th century already mention attempts to clear forest and drain wetlands in the central plain. Only from the 10th to the 13th centuries, however, did such work spread widely.

  That was the Medieval Warm Period, when European population nearly tripled. In northern and central Italy the urban population doubled. Cereals became a bigger part of the diet, so more land had to be cultivated. Monastic orders, feudal lords and free communes all joined the effort, and by the Middle Ages the valley was given over entirely to agriculture. Several of its older, smaller cities from ancient times remain there.

  Maps and documents show reclamation reaching its peak in the Renaissance, during the 15th and 16th centuries. It carried on through the 17th and 18th centuries. The last marshes were reclaimed only in the 20th century, and the channels and drains built along the way still keep the valley dry enough to farm.

  121920910

• 6. Peoples and Invaders

  ›

  About 780,000 years ago, the first big glaciation of the Pleistocene gripped Europe. Traces of people in the Po Valley go back at least that far. Sites such as Monte Poggiolo may have sheltered human groups fleeing the bitter cold of northern Europe. In warm periods the sea covered the valley. In glacial periods, lower seas left it open, and big mammals and humans could walk from Africa and the Middle East into western Europe without crossing the Alps. They reached as far as the Loire Valley and the Iberian Peninsula.

  Cities came much later here than in southern Italy or Greece. The first known inhabitants of the thick forests and swamps were the Ligurians, who may have been an Indo-European people. In the 7th century BC, Celtic peoples called the Insubres moved in, which is why northwestern Lombardy is sometimes called Insubria. The Etruscans conquered and colonised the southern and central regions in places. They left behind the names Parma, Ravenna, and Felsina, the old name of Bologna. Their rule brought urban civilisation but did not last, and by 500 BC migrating Gauls had pushed them out. The Venetics, probably a separate group of skilful merchants, took cultural influence from both Etruscans and Greeks.

  When the long Pax Romana weakened, the valley endured a string of Germanic invaders and even Attila and his Huns. The Gothic War and Justinian's plague devastated the population. Many people fled to the mountains, which stayed fairly populated until the 20th century. Into this desolation came the Germanic Lombards, a warrior people who gave Lombardy its name. In the Middle Ages the word covered all of northern Italy.

  The Lombards split their domain into duchies that often fought over the throne. Turin and Friuli, at the far west and east, seem to have been the strongest. The capital soon moved from Verona to Pavia, and Monza mattered more than ruined Milan. Their harsh, caste-like rule over the native population eased somewhat once they converted from Arianism to Catholicism.

  In 774, Charlemagne and his Frankish armies overthrew the Lombard kingdom. The valley became a prized part of the Carolingian Empire, as the kingdom of Italy, still with its capital at Pavia. In 962, Otto I of Saxony added the valley to the Holy Roman Empire. Meanwhile Venice rose from its lagoon as a sea power, allied with its former master, the Byzantine Empire. Towns grew rich on commerce and formed the Comuni, and Milan became the strongest city of the central plain. Frederick Barbarossa razed it in 1162, yet a Lombard League led by Milan, with the Pope's blessing, defeated him at the Battle of Legnano in 1176.

  168171819

• 7. Fog, Hail and Oak

  ›

  January temperatures in the Po Valley average between 0 and 5 degrees Celsius, and fog and mist are frequent. The climate is humid subtropical, shaped by a plain walled in by the Alps and the Apennines and open to the Adriatic Sea. Humidity stays high all year. Conditions grow warmer and more humid toward the south and east.

  Winters used to be foggier and colder. Urban heat, cleaner air and climate change have eased that. Snow and winter droughts can still starve the soil of the moisture that farming needs.

  July averages run between 22 and 25 degrees Celsius, according to 1971-2000 figures. Summer storms arrive often and suddenly. Hail can fall in large stones, rain can pour in large quantities, and crops can be destroyed. Supercell thunderstorms bring big hail and heavy agricultural losses, and tornadoes are common on the plains.

  Spring and autumn are well marked and pleasant. Along the lower Po, both winter and summer are harsher, while the Adriatic and the great lakes soften the weather nearby. Rainfall totals between 700 and 1200 mm a year and is spread evenly, with peaks in autumn and spring. Winds are usually weak, though sudden bursts of foehn wind or thunderstorms can sweep the air clean.

  Left alone, the Po basin would be a mixed broadleaf forest. Pedunculate oak, poplars, European hornbeam, alders, elderberry, elms, willows, maples and ash would all grow there, like trees found across central Europe. The largest surviving fragments stand around the River Ticino, protected as a Biosphere Reserve.

  814156

• 8. Breathing the Valley

  ›

  In March 2019, the European Space Agency published Sentinel-5P satellite images of nitrogen dioxide over northern Italy. They showed a large red area of nitrogen dioxide and fine particles sitting above the Po Valley, over Milan, Turin and Bologna. The valley is one of Europe's most important industrial and agricultural areas, and both roles feed the haze. Europe's worst air quality is found here.

  Milan and Turin share high levels of ozone and nitrogen oxides, produced mainly by diesel and petrol engines. On the farms, NPK fertilizers made of nitrogen, phosphorus and potassium add to the load. So does manure from intensive breeding. Lombardy alone supplies more than 40 percent of Italy's milk, and over half of Italian pig production is in the valley. The nearly enclosed basin and heavy road traffic complete the picture, since in winter cold air clings to the ground and traps the pollution.

  The Air Quality Life Index, built by the Chicago Energy Policy Institute to measure pollution worldwide, puts a figure on the harm. Its findings say that Po Valley air cuts about half a year from the life expectancy of the people who live there.

  In January 2021, The Lancet Planetary Health published research on death rates linked to fine particulate matter and nitrogen dioxide in 1000 European cities. Brescia and Bergamo in Lombardy had the highest death rates from fine particulates in Europe. Vicenza in Veneto and Saronno in Lombardy placed fourth and eighth. For nitrogen dioxide, Turin ranked third and Milan fifth. Verona, Treviso, Padua, Como and Venice ranked eleventh, fourteenth, fifteenth, seventeenth and twenty-third.

  Milan's metropolitan area ranks thirteenth for the impact of fine particulates. There, 3967 premature deaths occur in a year, roughly 9 percent of all deaths.

  2425262728