Luxembourg's geography: a country cut out of two plateaux

Why nothing in Luxembourg was pushed up

The two ends of the country's vertical range are a hilltop and a river bed. The highest point is the Kneiff, near Wilwerdange in the far north, at 560 metres; the Buurgplaatz near Huldange reaches 559 metres and the Napoléonsgaard near Rambrouch 554, which is a fair measure of how flat that ground is. The lowest point is the Moselle at Wasserbillig, 133 metres above sea level, where the river leaves for Germany. The 427 metres between those two figures are the entire relief of the Grand Duchy, and water made almost all of it by taking rock away.

The northern third is the Éislek, or Oesling, a corner of the Ardennes that carries on into southern Belgium. It is a plateau of schists and sandstones averaging 450 metres, and the flat top of that plateau is the original surface: the summits reach 450 to 560 metres because that is where the ground has yet to be removed. What gives the region its shape is a river network organised around the Sûre, which has incised deep valleys into the plateau from within. Settlement thinned out accordingly. Wiltz is the only town in the Éislek with more than five thousand people.

The southern two-thirds are the Guttland, or Bon Pays, averaging about 245 metres, and this is where the capital, the industrial towns and most of the population sit. Its surface breaks into distinct pieces, each one defined by what the rock does when water gets into it. The Luxembourg plateau in the south-centre is a large flat sandstone formation and carries the city. Little Switzerland, in the east around Berdorf and Beaufort, is craggy and thickly wooded, where erosion has opened gorges and caves and left a ruiniform topography of blocks that read as collapsed masonry; the great beech forest of the Mullerthal grows on it. The Moselle valley along the south-eastern border is the lowest ground in the country. The Red Lands in the far south and south-west hold the iron field and the largest towns after the capital.

All of it comes to 2,586 square kilometres, 82 kilometres long and 57 kilometres wide.

How the rivers ended up as borders

Almost the whole of Luxembourg drains into one basin, the Moselle's, and the rivers doing the draining also do the dividing.

The eastern border is water along its full length. The Our, the Sûre and the Moselle succeed one another from north to south, so the line with Germany is a set of channels rather than a survey. The Sûre is the longest river in the country: it rises in Belgium and runs 172 kilometres eastward before joining the Moselle, and its sinuous course cuts Luxembourg from one side to the other. The mid-Sûre and Attert valleys form the boundary between the Guttland and the Éislek, which makes the internal division of the country a river as well.

The Moselle rises in north-east France and flows north through Luxembourg for 31 kilometres on a course of 544 kilometres that ends at the Rhine in Koblenz. Canalisation has made 64 kilometres of it navigable, and the port at Mertert connects the Grand Duchy to the Rhine waterway system. For a landlocked country separated from the North Sea by Belgium, that is the only water route out.

The western border was drawn by people instead. Luxembourg was partitioned three times, in 1658, 1815 and 1839, and the third partition ceded the geographically larger, predominantly Oil-speaking western part of the duchy to Belgium as the province de Luxembourg. What was left is the country now on the map: a shape whose eastern edge was cut by rivers and whose western edge was cut by a treaty.

What the Alzette and Pétrusse cut out

Two Roman roads crossed on the plateau above the Alzette and the Pétrusse, one running from Arlon to Trier and one to Thionville, and a circular wooden palisade was thrown around the crossing so that farmers in the region could shelter there. On the Bock promontory beside it stood a small Roman fortification called Lucilinburhuc, little fortress, a name that became Lützelburg and then Luxembourg. In 963 Count Siegfried of the House of Ardennes obtained the land from St Maximin's Abbey in Trier in exchange for his territories at Feulen near Ettelbruck, and built a castle on the promontory, reached from the plateau by a drawbridge.

UNESCO's inscription describes the site as a very steep rocky outcrop at the confluence of the two rivers, a natural fortification that only needed to be completed on the west side. Most of what the city became follows from that sentence. Knights and soldiers were billeted on the outcrop and artisans and traders settled beneath it, which is the origin of the long-standing social distinction between the upper and the lower city. The walls then went outward in stages: one by the 12th century along what is now the Rue du Fossé, a second in the 14th century taking in the Rham plateau, a third as far as today's Boulevard Royal.

After that the defenders went back into the rock. Austrian engineers under Charles VI and Maria Theresa dug nearly 25 kilometres of casemates into the bedrock and closed the valley with locks. In its final form the fortress held 23 kilometres of underground passages connecting over 40,000 square metres of bomb-proof space, and covered about 180 hectares at a time when the city itself covered only 120. Commander Neipperg had the soil stripped to bare rock for 600 metres out from the walls so that besiegers would have nothing to dig trenches in, and the ring of stone that produced was called the champs pelés, the bare fields. The fortress was never taken by force. Most of it was demolished after the Treaty of London of 1867, and what survives of the works and of the old quarters has been on the UNESCO World Heritage list since 1994.

Where the good land begins

Gutland means good land, and the name is a comparison with the north: the soil is more fertile and the summers warmer and drier than in the Éislek. Vegetables and fruit are grown there in quantity, strawberries and apples and plums and cherries among them. The same ground has been cut into deep gorges and caves by river erosion.

The Éislek got the opposite deal. Its mountain soils are thin and hard to cultivate, so most of the land there is under cattle pasture, and the fertility it does have was in large part bought: the introduction in the 1890s of a basic-slag fertiliser, a by-product of the grand duchy's steel industry, greatly improved it. Ore mined in the far south went to feed the plateau in the far north.

The best ground in the country is on the slopes above the Moselle, carved in chalk and calcareous clay, which take a substantial amount of sunshine and have earned the valley the name Little Riviera. Vineyards line 42 kilometres of it from Schengen in the south to Wasserbillig in the north, and most of the villages on that stretch have at least one winery. The fertile soils of the Moselle and lower Sûre valleys carry rich pasture as well.

For a country whose relief is mostly a set of cuts, the share of it under the plough is modest. Arable land accounted for 23.9% of the territory and permanent crops for 0.56% as of 2011. Agriculture employed about 2.1% of the active population in 2010, when there were 2,200 holdings averaging 60 hectares, and about half of the country's farms are smaller than 50 hectares. Livestock and their by-products make up the bulk of what is produced, with cattle gaining at the expense of pigs and sheep, and cereals and root vegetables behind them.

Why the north and south get different weather

The climate is oceanic, Köppen Cfb, mild without extremes and wet, and the difference between the two halves of the country is a difference of exposure. The Éislek takes the Atlantic systems more directly: frequent pressure depressions, unstable conditions, overcast skies and drizzle through the winter, and cool summers in which the temperature drops sharply at night. The south is no milder in winter. Its advantage shows up in summer, and most of all in the sheltered Moselle valley, which is warmer and sunnier than anywhere else in the Grand Duchy, which is why the grapes are there.

Rainfall does not follow the north-south line neatly. The Oesling receives more precipitation than the Bon Pays overall, yet both national extremes sit in the south: about 1,000 millimetres a year in the south-west against about 685 millimetres in the south-east. Mean annual temperature runs around 10 degrees Celsius, and the sunniest months are May to August.

The long record is at Findel, the airport station east of the capital, which has been measuring since 1947.

Recent years have run above the normal. 2024 came in at 10.5 degrees, the eighth warmest year at Findel and 0.7 degrees above the reference period, with the record still held by 2020 at 11.3 degrees. February 2024, at 6.5 degrees, was the warmest February in the whole record, ahead of February 1990 at 5.9. Snow behaved to match: nine days with cover that winter against a normal of 21.

The extremes arrive as water rather than as heat. Summer 2024 averaged exactly the 1991 to 2020 figure of 17.9 degrees, with 30 days above 25 degrees against a normal of 31.5 and four days above 30 degrees against a normal of 7.2, and no night at or above 20 degrees at all. What did the damage was convective. On the evening of 29 June 2024 an organised storm system crossed most of the country, dropping 30 to 60 litres per square metre in an hour on the south-west and west and driving gusts of 80 to 100 kilometres an hour; Luxembourg insurers counted 24.5 million euros of claims. Torrential rain on 17 May 2024 flooded ground again, and an episode of freezing rain on 17 January 2024 put the whole country under a red warning.

Why the forest stopped storing carbon

The third national forest inventory was carried out between January 2023 and July 2024 on 1,845 sampling points. It found the forest area steady at about 35% of the territory, 92,250 hectares, split almost exactly between public ownership at 49.5% and private at 50.5%. Several indicators had improved. Broadleaves rose from 66% of the stock in 2010 to 75% in 2023, the number of old large-diameter trees more than doubled after 2000 to reach nearly 135,000 by 2023, and deadwood went from 6 to 27 cubic metres per hectare, which counts as habitat.

The volume figures went the other way. Standing timber had grown 18% between 2000 and 2010; by 2023 it stood more than 6% below the 2010 level, leaving total growth across the 23 years at 11% despite older stands and a larger average diameter. Increment fell 21% in broadleaf stands and 32% in conifer stands, and the volume of growth over 2010 to 2023 was down 25% against the previous period. Between 2010 and 2023 the country's forests released more carbon than they absorbed and became a net source of emissions.

Drought is the mechanism, and bark beetle is what follows it. Prolonged dry spells killed trees outright and let the beetle into the spruce, and clearfelling of infested spruce rose from 850 hectares at the second inventory to 2,050 hectares at the third. STATEC recorded 58.4% of trees significantly damaged in 2024. A new forest code, the law of 23 August 2023, applies sustainable management rules to public and private woodland alike, and a national forest programme was being finalised on the third inventory's results.

What grows there sits on the boundary between the Atlantic-European and Central-European climate zones. Beech and oak dominate in the north, where oaks reach 30 to 45 metres with trunks 1.2 to 2.4 metres across and supply hardwood timber prized for its strength. Black alder and willow hold the riverbanks, alder being durable even under water. The narrow, deeply incised valleys of the north are also where the European otter, a protected species, has held on.

What the iron ore left in the south

The extreme south is the land of the red rocks, named for the mineral in the ground rather than for anything above it. The ore field stretches for over 19 kilometres along the French border, continuing out of Lorraine into the south-western corner of the duchy, and it has been mined and worked since Roman times if not earlier.

That ore is high in phosphorus, which made it useless for steel until the basic Bessemer process arrived in 1879. Afterwards the metallurgical industries grew fast enough to define the country. Steel accounted for as much as 80% of the value of Luxembourg's exports in the 1960s, ARBED had been producing it at Belval since 1911, and the tall chimneys of the ironworks and steelworks became the landmarks of the industrial south. The deposits were exhausted by the 1980s.

What the field left behind is the other half of the story. The official inventory of the country's natural resources runs to two entries: iron ore, no longer exploited, and arable land. Esch-sur-Alzette, Pétange, Differdange and Dudelange grew on the ore and stopped growing when western European steel contracted in the late 20th century. Among the abandoned quarries and worked-out open pits, plants have taken the ground back and flowers are everywhere. At Belval, where blast furnaces and factory halls defined the character of the ground for almost a hundred years, the plant was shut down in the 2000s and the site reused. The two surviving blast furnaces, the last in the country, have been protected as industrial monuments since 18 July 2000, and the Cité des Sciences campus of the University of Luxembourg was built around them.

Where the country keeps its water

Total renewable water resources come to 3.1 cubic kilometres, and irrigation barely features: 10 square kilometres of irrigated land on a 1993 estimate that counts Belgium in with it.

Storage is concentrated in one place. The Upper Sûre lake is the largest stretch of water in the Grand Duchy, formed by a dam built above Esch-sur-Sûre in the 1960s to meet the country's drinking water requirements, with the reservoir extending some 10 kilometres up the valley. The dams on Luxembourg's rivers are also its only domestic source of power, and the hydroelectricity they generate covers about a fifth of national energy needs. The rest is imported, and nuclear generation is negligible.

The lake carries sailing, canoeing and kayaking, and the growth of those activities has supported a local crafts industry around it. The Upper Sûre National Park in the Ardennes is the main conservation area in the country. The arrangement is consistent with everything else here: the deepest cut in the plateau holds the drinking water, makes the electricity and takes the walkers, because there was never any other kind of ground to put them on.