Why Georgia's rivers run to two different seas

How the Likhi Range splits Georgia in two

Between the Greater Caucasus on the Russian border and the Lesser Caucasus in the south lies a long structural trough, and two short ranges cross it. Britannica names them the Meskhet and Likh ranges and says they link the two mountain systems and mark the watershed between the basins of the Black and Caspian seas. Wikipedia calls the barrier the Likhi Range, and also the Surami Range, the ridge that connects the Greater and Lesser Caucasus, and its country article says the range divides Georgia into eastern and western halves. In antiquity those halves had separate names. The west was Colchis and the eastern plateau was Iberia.

Water decides which half a place belongs to. Rivers west of the ridge run to the Black Sea. Rivers east of it join the Kura, which leaves Georgia through Azerbaijan and ends in the Caspian. The same ridge, with the Meskheti Range, often blocks the humid air that comes in off the Black Sea, so the rain divides along it as well, and with the rain the forests, the crops and the pattern of settlement.

Greek geographers drew a line through this country too, though on a different axis. Anaximander put the boundary between Europe and Asia along the Phasis, the river now called the Rioni, which placed northern Georgia in Europe and the south in Asia, and Herodotus followed him. One eighteenth-century definition moved the line north to the Kuma-Manych Depression and put the whole Caucasus in Asia; another drew it at the Aras and put all of Georgia in Europe. The line the land draws for itself runs north to south across the middle.

What the Greater Caucasus does to Georgia

Along the whole northern border stands the Greater Caucasus, which Britannica describes as a series of parallel and transverse belts rising eastward and cut by deep gorges. It carries every summit in Georgia above 5,000 metres, and the sources do not agree on how high the tallest of them is. The country record gives Shkhara as 5,193 metres. Wikipedia prints 5,203 metres, and Britannica prints 5,068 metres, a spread of 135 metres over a single summit. This article uses the record's figure and notes the other two.

The other named peaks are Janga at 5,059 metres, Kazbek at 5,047 metres, Shota Rustaveli Peak at 4,960 metres, Tetnuldi at 4,858 metres, Ushba at 4,700 metres and Ailama at 4,547 metres, all in Wikipedia's figures. Kazbek is the odd one. It is the cone of an extinct volcano, which Britannica gives by its Georgian name Mkinvari, and it is the only one of those peaks of volcanic origin. The 200 kilometres of the main range between Kazbek and Shkhara are dominated by glaciers.

The range is a wall against cold air from the north, and the mild winters of the western lowlands follow from that. It holds snow, which often lies more than two metres deep on the foothills and mountains of the west, and many mountain villages are cut off in winter because of their altitude and the poorly developed roads that reach them. It also leaves only a few ways through. The main roads into Russia run through the Roki Tunnel between Shida Kartli and North Ossetia and through the Darial Gorge in Khevi.

A few slivers of Georgian territory lie north of the Caucasus watershed, in the North Caucasus proper. Spurs such as the Lomis and Kartli ranges run south from the crest at right angles to the main line, and from the ice on these high flanks come many of the rivers of both halves.

Why western Georgia stays wet and green

West of the Likhi Range, the Kolkhida Lowland is the flat heart of ancient Colchis, where the Argonauts of legend came for the Golden Fleece. It is built of river deposits laid down over thousands of years by the Inguri, the Rioni and the Kodori as they come out of the Greater Caucasus and spread across the plain to the sea. It was formerly an almost continuous swamp. Soviet engineers dug drainage canals, built embankments, straightened stretches of river and planted trees, and the lowland along the coast became farmland for subtropical and other commercial crops. The Wikipedia article on the Georgian economy lists citrus fruits, tangerines in particular, and tea among the country's traditional mainstays.

Rain falls through the whole year, between 1,000 and 2,500 millimetres annually on the western lowlands, with the maximum in autumn and winter. Southern Kolkhida is the wettest part, and the port of Batumi receives about 2,500 millimetres a year. Winters are mild. The midwinter average on the coast is about 5 °C and the midsummer average about 22 °C, and below about 650 metres the climate stays subtropical. Above that come a band of moist, moderately warm weather, then a band of cool and wet conditions, and alpine conditions from about 2,100 metres.

Farming and towns took most of the original cover. Much of the natural habitat of the western lowlands has disappeared over the past hundred years, and the forests that covered the Colchis plain now survive mainly inside national parks and reserves such as the area around Lake Paliastomi. Temperate rainforest remains on the west-central slopes of the Meskheti Range in Ajaria and in parts of Samegrelo and Abkhazia. UNESCO inscribed the Colchic Rainforests and Wetlands on the World Heritage List in 2021, the only natural property among Georgia's inscriptions.

What survives in the Colchic forests

Britannica attributes the survival of relict species in the west to a climate that has stayed relatively constant over a long span. The Pitsunda pine is one. The western forests carry oak, chestnut, beech and alder, with an evergreen understorey of rhododendron and holly and lianas climbing through some stands. Below about 600 metres the trees are mainly deciduous, with box among them. Between 600 and 1,000 metres beech, spruce and fir mix in, and above 1,500 metres the forest turns largely coniferous up to a tree line at about 1,800 metres.

About 1,000 of Georgia's 4,000 higher plants are endemic, in Wikipedia's figures. The common pheasant, also called the Colchian pheasant, is listed as endemic to Georgia and has been introduced as a game bird across much of the world. The Rioni may still hold a breeding population of the bastard sturgeon, which is critically endangered.

How eastern Georgia dries out towards the Caspian

East of the ridge the Black Sea's influence fades. Wikipedia describes the climate as transitional between humid subtropical and continental, fed by dry Caspian air from the east and by whatever humid Black Sea air gets past the Likhi and Meskheti ranges from the west. Rainfall on the plains and foothills averages 500 to 800 millimetres a year, roughly double that in the mountains, and it falls mainly in spring and autumn. Summers on the plains average 20 to 24 °C and winters 2 to 4 °C. Britannica adds that eastern Georgia, farther inland, is colder than the west at the same altitude.

The central plain is Kartli, a high plateau enclosed by mountains on four sides and covered mostly by loess, stretching along the Kura between Khashuri and the old capital Mtskheta. The Kura is the organising river of the east. It flows 1,364 kilometres from north-eastern Turkey across the eastern plains and through Tbilisi before reaching the Caspian.

The land gets drier towards the south-east. The Iori Plateau is semi-arid, and in Dedoplistskaro Municipality, at the country's eastern edge, annual precipitation fluctuates between 300 and 648 millimetres and the land is at high risk of desertification, in the figures the UNEP and GRID-Arendal outlook on the South Caucasus mountains compiled. Agriculture accounted for about 70% of the municipality's output in a 2012 estimate the outlook cites, mainly wine, cereals, vegetables and livestock.

The forests change with the climate. Nearly 85% of eastern forest is deciduous, mostly beech, oak and hornbeam, with conifers dominant only in the Borjomi Gorge and at the western extreme. Above 1,000 metres in Tusheti, Khevsureti and Khevi, pine and birch take over. The Alazani Valley in Kakheti holds the only large lowland forest left in the east, and elsewhere on the plain Britannica describes steppe with thickets of thorny scrub and a cover of feather grass and beard grass.

What the southern volcanic uplands hold

The Lesser Caucasus runs parallel to the Turkish and Armenian borders and is joined to the Greater Caucasus by the Likhi Range. It is much lower, a set of interconnected ranges and plateaus largely of volcanic origin that do not exceed 3,400 metres. It reaches 10,830 feet at Didi-Abuli in Britannica's figure, about 3,300 metres.

Wikipedia lists the Javakheti Plateau among its main features, along with the lakes Tabatskuri and Paravani and a supply of mineral water and hot springs. Mineral water appears on Georgia's list of main exports for 2015 in the Wikipedia economy article. Wikipedia credits the Lesser Caucasus and the Surami Range, which connects the two mountain systems, with forming natural barriers that are partly responsible for the cultural and linguistic differences between Georgian regions.

How much of Georgia's coast Tbilisi governs

The area figure depends on the source and on what it counts. The country record and Britannica both give 69,700 square kilometres. Wikipedia's country article gives 67,900. Britannica adds a second figure, 57,612 square kilometres, for Georgia excluding Abkhazia and South Ossetia, so about 12,100 square kilometres of the total lie in the two regions the government in Tbilisi does not administer. Georgia: history covers how that came about, and the site records the two figures without taking a position on the dispute.

The coast shows the gap more sharply than the area does. Georgia's Black Sea coastline runs about 315 kilometres, and 200 kilometres of it lie in Abkhazia, against 57 kilometres in Ajaria. The Exclusive Economic Zone covers 21,946 square kilometres of the Black Sea. The northernmost and westernmost points of Georgia are both in Abkhazia de jure; the de facto northernmost point is in Mestia Municipality and the de facto westernmost in Adjara.

People are concentrated in the narrow valley between the two mountain systems and along the Black Sea coast, and population density falls as altitude rises, in Britannica's description. The country record gives 3,929,581 people on 14 November 2024, and 1,331,485 of them, about a third, lived in Tbilisi on the Kura in the eastern half.

Where the Georgian ground gives way

Steep, wet mountain ground moves. Georgia's Third National Communication to the UNFCCC, published in 2015 and summarised in the UNEP outlook, put almost 70% of the territory, home to some 57% of the population, at risk from natural disasters. The four shares below add up to 100%, more than the 70% total, because one slope can carry more than one hazard.

The same communication found that landslides had increased by 63% since 1987, and it attributed the rise to population growth, clearing of vegetation from slopes, building on unstable soils, artificial waterways, increased tectonic activity and warmer, wetter weather. In 1989 massive rock slides and mudslides in Ajaria displaced thousands of people in the south-west. Two earthquakes in 1991 destroyed several villages in Racha, upper Imereti and the Tskhinvali Region.

The capital is exposed as well. In June 2015 heavy rain triggered landslides that sent debris into Tbilisi, killing 19 people and causing about US$100 million in economic losses, according to the outlook.

The risk differs between the two halves. The Rioni basin in the west is identified in the national communications as the area most sensitive to climate change because of its exposure to floods, and about 71% of people there work in agriculture. In the east the danger is drought, whose frequency has increased almost threefold in recent years, mostly in Shida Kartli, Kvemo Kartli, Kakheti and upper Imereti, as the outlook reported in 2015.

How the ice and the rivers are changing

The National Environmental Agency counts 383 glaciers in Georgia, covering 377 square kilometres, in the 2015 inventory of Caucasus glaciers. They sit mainly in the basins of the Enguri, Rioni, Kodori and Tergi, where peaks rise above 3,500 metres, and the Enguri basin alone holds 35.9% of them by number and 62.8% by area. Both the number and the area have fallen, and the agency found the decrease more intense in eastern Georgia than in western.

The Chalaati glacier retreated 436 metres between 1974 and 2011, the UNEP outlook reports, and the Tviberi glacier shrank from 43.1 to 23 square kilometres by the time of the outlook's 2015 figures, splitting so that the Kvitlodi glacier now lies 800 to 900 metres from it. Between 1985 and 2000 the number of glacial lakes in the Greater Caucasus grew by 50%, in the 2015 national communication's figure, and each adds to the risk of an outburst flood downstream.

The climate record splits along the Likhi Range too. Between the periods 1961 to 1985 and 1986 to 2010 the west warmed by 0.3 °C and the east by 0.4 to 0.5 °C. Precipitation rose in the west, by about 14% in the Svaneti mountains and in the mountains of Adjara, and fell on the Likhi Range and to the east of it. The 2015 national communication projected a further 0.8 to 1.4 °C of warming by 2050 and 2.2 to 3.8 °C towards 2100.

Rivers carry most of Georgia's electricity, which makes the ice an energy question. Wikipedia's geography article counts about 25,000 rivers; the Ministry of Energy estimate cited in the economy article puts it at around 26,000, with approximately 300 significant for power. Hydropower produced 6.17 billion kWh in 2005, 86% of generation, and the Inguri plant has an installed capacity of 1,300 megawatts. In 2013 Georgian hydropower plants generated 7,900 GWh against a potential hydro resource of 31,500 GWh and consumption of 9,700 GWh, in the outlook's table. Glacial runoff on the Inguri is projected to fall by 40% by the end of the century compared with 2010, taking the river's annual runoff down by about 13%. Georgia: economy covers what the power is used for, and Georgia: travel the parts of both halves a visitor reaches.