Bosnia and Herzegovina's geography: two seas and one short coast

Where the rain on Bosnia and Herzegovina ends up

Bosnia and Herzegovina sits across a drainage divide, and the divide is lopsided. The World Bank's climate risk profile of 2021 describes the country as lying within the Adriatic and Black Sea basins, and names the two river systems that share its water: the Sava basin in the north, gathering the Una, the Vrbas, the Bosna and the Drina, and the Adriatic basin in the south, made up of the Neretva and the Trebišnjica. The Sava is a tributary of the Danube, so everything collected on the northern side belongs to the Black Sea basin.

The International Sava River Basin Commission publishes the split country by country. It puts 38,349 square kilometres of Bosnia and Herzegovina inside the Sava basin, which is 75% of the national territory. Bosnia and Herzegovina's portion makes up 39.5% of the whole catchment.

The commission gives the population living inside that catchment as 2.946 million people, or 87% of the country's inhabitants, and the table does not say which year it counted them in. Settlement leans the same way: Britannica notes that the arid southern plateaus hold fewer people than the central and northern zones.

The water itself is plentiful. The World Bank profile puts the average flow of the country's rivers at about 1,555 cubic metres a second, and it estimates that roughly 57% of that water leaves the country unused, which it attributes to infrastructure damaged in the war and to a lack of investment since. Total renewable water resources were recorded at 37.5 cubic kilometres in 2011.

Part of that flow is turned into electricity. As of 2018 the country had about 2,076 megawatts of net installed hydropower capacity, beside 2,065 megawatts of lignite, 159 of small hydropower and 51 of wind. Generation runs at around two thirds coal and one third hydropower, and the balance moves with the rivers: in a dry summer the hydropower share falls, and the World Bank profile expects reduced summer rainfall inland to cut it further.

How the Dinaric Alps rise towards the south

The Dinaric Alps occupy the centre of Bosnia and Herzegovina and run in parallel ranges from northwest to southeast, and they rise as they go south. Britannica lists the Kozara, Vlašić, Plješevica, Grmeč, Cincar and Raduša among the ranges crossing the country on that alignment. Maglić, at 2,386 metres, stands on the frontier with Montenegro in the southeast, and it is the country's highest point.

The World Bank profile divides the land into four kinds of ground, and the proportions explain why the country reads as mountainous on any map.

The average altitude is about 500 metres. Lowland in the strict sense covers a twentieth of the territory, and most of it lies in the north, where narrow plains follow the Sava and its tributaries.

The rock is mostly limestone, including Mesozoic limestone, and the ranges carry deposits of iron, coal, zinc, manganese, bauxite, lead and salt, concentrated in central and northern Bosnia. Mining here is old. The geography article on Wikipedia identifies three historic ore districts: the central Bosnian mountains between the Vrbas, Lašva, Neretva and Rama, a western district between the Vrbas and the Una centred on the Sana and Japra valleys, and an eastern district along the Drina between Foča and Zvornik, centred on Srebrenica. It dates the working of these ores back more than 5,000 years.

The mountains are also faulted. Britannica describes fault lines as widespread across the upland, and in 1969 an earthquake destroyed 70% of the buildings in Banja Luka. The World Bank profile of 2021 notes that no national seismic risk assessment has been carried out, and cites an analysis of present-day exposure estimating that the same earthquake would now cause more than 400 deaths and more than US$4 billion in damage.

The two names in the country's title are regions, and they follow the relief loosely. Bosnia covers the northern part, roughly four fifths of the territory, and Herzegovina the south. The boundary between them has never been defined.

Why rivers in Herzegovina run underground

South and southwest of the high ranges the ground changes character. Britannica calls this belt the Karst: plateaus of arid limestone, often bare and denuded where forest was cleared and the soil was too thin to hold, with elevations above 1,800 metres common and an abrupt descent toward the Adriatic. The limestone is riddled with caves and potholes and drains underground, and Britannica states plainly that rivers in the Karst flow largely below the surface.

Between the ridges lie poljes, closed depressions floored with alluvial soil, which are the farmable land of the south. In the municipality of Ravno one protected landscape takes its name from Popovo polje together with a cave, Vjetrenica.

UNESCO inscribed Vjetrenica Cave, Ravno as a natural World Heritage site in 2024. The cave measures 7,324 metres in length and forms part of the Trebišnjica river system. At inscription UNESCO recorded more than 230 taxa in the cave system, including 180 animals, 14 fungi and 35 protists. Of these, 93 are troglobiotic, meaning they live only underground: 48 aquatic and 45 terrestrial. Forty were described to science for the first time from specimens taken in the cave. Nine species of the amphipod genus Niphargus live there together, and 78% of the cave's aquatic fauna is found nowhere outside the Dinaric region.

Two animals in the inscription have no counterpart elsewhere, in UNESCO's wording: Vjetrenica is habitat for "the only subterranean tubeworm in the world", Marifugia cavatica, and for "the only freshwater hydrozoan living exclusively in groundwater", Velkovrhia enigmatica. The protected cave covers 22.87 hectares inside a property of 413.97 hectares, and the whole of it sits within the Vjetrenica-Popovo Polje Protected Landscape. UNESCO's assessment singles out changes to the water regime upstream as the pressure the cave fauna is most exposed to.

At Blagaj karst water returns to the surface in a strong spring, Vrelo Bune, which feeds the Buna. The river flows west for about 9 kilometres before joining the Neretva. The Neretva itself is the main surface river of the south. It comes from the southeast, turns sharply southwest through the karst, passes Mostar and crosses into Croatia before reaching the Adriatic.

Which rivers carry Bosnia north to the Sava

The rivers on the Black Sea side run the other way, north out of the mountains toward the Sava, which forms the northern boundary with Croatia. Wikipedia's geography article lists seven principal rivers, and six of them belong to this side.

The Una flows along the northwestern border with Croatia and through Bihać, and takes in the Sana from Sanski Most and Prijedor. The Vrbas crosses the centre of the country from Gornji Vakuf through Bugojno, Jajce and Banja Luka to the Sava. The Bosna runs from its source near Sarajevo to the Sava without leaving the country, and it gave its name to Bosnia. The Drina, in the east, forms the border with Serbia in many places and passes Foča, Goražde, Višegrad and Zvornik. The Sava touches Bosnia and Herzegovina only as a boundary, along a Posavina plain holding Brčko, Bosanski Šamac, Bosanski Brod and Bosanska Gradiška.

The Posavina is very fertile land. It is part of the Pannonian lowland stretching into Croatia and Serbia, and it is heavily farmed. In 2012, 19.73% of the land was classed as arable and 2.06% as permanent crops. The World Bank profile puts agricultural land at 46% of the country and records that irrigation reached only 0.65% of arable land in 2013, so almost all of it depends on rain.

The northern basin also floods. More than 20% of the territory is prone to flooding, which on the World Bank's figures affects around 100,000 people a year. In 2014 rainfall of a volume the profile calls unprecedented inundated farmland and 81 municipalities, affected a quarter of the population and set off more than 3,000 landslides. The EM-DAT disaster database, as cited in the same profile, counts eleven riverine floods in the country from 1900 to 2020, with 29 deaths and 1,329,340 people affected. The profile lists 2001, 2002, 2009, 2010 and 2014 as flood years.

How long the coast at Neum measures

On the Adriatic side the country reaches the sea along one short strip around the town of Neum, in the Herzegovina-Neretva Canton. Croatian territory closes it in on both sides, and Croatian peninsulas surround the town. Under the United Nations Convention on the Law of the Sea, Bosnia and Herzegovina holds a right of innocent passage from Neum to the open sea. Britannica records that the strip contains no natural harbour.

Its length depends on who measured it, and the sources on file disagree by more than a quarter. So do their figures for the land borders.

Wikipedia's tourism article gives the coast at Neum as 24.5 kilometres. None of these sources explains its method. For the Serbian border the spread runs from 302 to 375 kilometres, and none of the sources says where the difference arises.

The sea itself is small. The World Bank profile gives the country's total surface area as 51,209 square kilometres, of which 51,197 are land and 12.2 are sea.

Why the mountains hold back the Mediterranean climate

The Mediterranean lies close to Bosnia and Herzegovina, and most of the country does not feel it. Britannica describes Bosnia and Herzegovina as largely cut off from the sea's climatic influence by the Dinaric Alps. North of the ranges the weather resembles that of the southern Austrian highlands, mild in most seasons and bitterly cold in winter. In Banja Luka the average temperature is about 0 °C in January and about 22 °C in July, and the wettest months are May and June.

Herzegovina, on the seaward side of the divide, has more in common with Dalmatia. In Mostar, on the Neretva, January averages about 6 °C and July about 26 °C. The summer from June to September is relatively dry, and the heaviest rain comes from October to January, the reverse of Banja Luka, where January and February are the driest months.

The World Bank profile names three climates: temperate continental on the Sava lowlands and the foothills, alpine in the mountains, and Mediterranean on the coast and in the lowland of Herzegovina. Across the whole country, the 1991 to 2020 climatology gives a mean annual temperature of 10.24 °C and mean annual precipitation of 1,109 millimetres. Monthly means run from 0 °C in January to 19.5 °C in July and August. The same document's text gives annual rainfall as 553.3 millimetres, half the figure in its own table, and does not reconcile the two.

Those means have been moving. From 1981 to 2010 summer temperatures exceeded the earlier norms by 1.2 °C and winter temperatures by 0.8 °C, and the steepest rise has come since the early 2000s. Over the same period rainfall increased in the central mountains and fell by as much as 20% in the northern regions in summer. The number of days with rain has declined while the intensity of rainfall has increased.

The dry years are listed as 2003, 2007, 2008, 2011, 2012 and 2013. The drought and record heat of 2012 cost an estimated US$1 billion in lost farm output and destroyed almost 70% of the vegetables and maize grown in the inland areas. Mostar, Bijeljina, Brod and Tuzla are named as the farming districts most affected by soil water shortage.

What covers the land between the ridges

Forest is the most extensive surface cover, and the sources on file give three different figures for it. Britannica says about two fifths, the country article on Wikipedia says nearly half, and the geography article gives around 43% of the land area, equal to 2,187,910 hectares of forest in 2020, down from 2,210,000 hectares in 1990. In 2015, 74% of the forest was in public ownership and 26% was private. Most of the forest lies in the centre, the east and the west of Bosnia, and eastern Bosnia is heavily wooded along the Drina.

Britannica names pine, beech and oak as the forest trees. It lists bears, wolves, wild pigs, wildcats, chamois, otters, foxes, badgers and falcons among the fauna, and among the common fruit it singles out plums. The WWF divides the territory into ecoregions, three according to the geography article: Pannonian mixed forests, Dinaric Mountains mixed forests and Illyrian deciduous forests. The country article adds a fourth, Balkan mixed forests.

Beech forest is also the country's other natural World Heritage listing. Bosnia and Herzegovina is a state party to the serial property of Ancient and Primeval Beech Forests of the Carpathians and Other Regions of Europe. Three more natural places are on its tentative list with UNESCO: the natural and architectural ensemble of Blidinje, entered in 2007; the Strict Nature Reserve of Perućica, a primeval forest inside Sutjeska National Park, entered in 2017; and the complex of travertine waterfalls at Martin Brod in Una National Park, entered in 2019.

The mountains above the forest carry the winter sports ground. Trebević, Jahorina, Igman, Bjelašnica and Treskavica, in the east near Sarajevo, held the 1984 Winter Olympics, and Vlašić, Čvrsnica and Prenj stand in the central ranges. Britannica also records glacial lakes scattered across the upland, and natural springs, many of them bottled as mineral water or used for thermal spas.