The chief river is the Dnieper (q.v.) which has formed one of the links between the Black Sea and the Mediterranean and the Baltic from ancient times. The .Pripet river joins the Dnieper a little south of the northern boundary of the Ukraine and almost doubles its volume, the Dnieper from this point often dividing into two or more channels, and having many islands. The right bank is high and rocky and the left a low plain, though in three places the plain extends along both banks. During the melting of the snows the river overflows the islands and the plains along its shores, leaving them covered with fertile alluvium. At the mouth of the left bank Samara tributary both banks of the Dnieper be come precipitous. The post-Tertiary elevation of the Azov horst forced the river to dig its bed into the granite-gneiss rocks, but in many places ledges of these rocks lie across its path and it descends in a series of waterfalls, now being harnessed for produc tion of electric energy. Below the falls the river expands, flowing in several channels, and silting up its liman so quickly that con stant dredging is necessary to keep the port of Kherson open even for small sea-going vessels. Of its numerous Ukrainian tribu taries, the Teterev and Ingulez on the right, and the Desna on the left, are the most important, the latter being navigable for a great distance.
The present scheme of electrification of the falls includes a scheme for deepening the river channel so as to make it available for large steamers and for providing adequate canals in this region. The lower course of the Dniester (q.v.) forms the bound ary between Bessarabia and the Ukraine. Its left bank Ukrainian tributaries are short, and flow from the Volhynian-Podolian plateau. They are full at the melting of the snows and have carved deep canyons, but in summer they almost disappear. Between the Dniester and the Bug, no river reaches the sea, all being shut in by limans. The Bug (Boh) is a shallow stream, not navigable even after the spring thaws except near its mouth, and its tributaries in summer become mere chains of ponds; rapids are formed in its bed by ledges of the granite-gneiss horst. The upper course of the Donetz with its white chalk cliffs lies in the Ukraine. On the whole the waterways of the Ukraine are not favourable to navigation, the Dnieper and its tributaries giving the greatest possibilities. In 1926-27 there were 76 motor driven boats and 188 barges on the rivers and the freightage carried, mainly grain, timber and metal goods, was 872,000 tons, the number of passen gers being about two million.
snow hardly remains at all, this being a contributory cause of bad harvests. Sometimes these east winds bring snow and are so cold and violent that the flocks of sheep are destroyed.
Other causes of bad harvests are a rainless spring, and the re turn of easterly winds and frosts in May. The maximum rainfall is in summer and falls mainly in heavy showers which may wash away parts of the surface and which, in any case, run off quickly. Winter is severe, the average temperature at Kiev, lat. 50° 30' N., in January being I° C, colder than that of Hammerfest, lat. 70° 35' N. The duration of frost on the Pontic steppe is 2 months and in the rest of the Ukraine 3 to 4 months. Spring in the south is liable to dry east winds bringing sandstorms, but towards the north-west it is moister, with frequent alternations of snow and frost. In summer most of the Ukraine lies south of the 20° C isotherm and high temperatures prevail in the south in July and August. The amount of rainfall diminishes from the north-west (55o mm.) to the south-east (30o mm.) and yearly fluctuations especially in the important spring rains are great ; the bad harvests of 1921 and 1924 were due to spring droughts.
Forests.—In former times forest and forested glades covered much of the area, coniferous in the north and west, and oak in the south, and patches of forest still remain especially in the north west and in the Kharkov district. The beech occurs in a small region west of Kamenets Podolsk. The Pontic steppe is practi cally treeless and probably never had much forest except along the Dnieper river, where it still extends as far as Kherson and is found in patches south of that town. Forest clearing was going on as early as the time of the Kiev principality. Later the Mongols and Tatars destroyed huge stretches of forest by setting fire to it, partly to provide pasture grounds for their flocks and partly to pre vent the Slays from taking refuge in the forest. In the 16th cen tury the colonising Cossacks continued the process and also prac tically exterminated the wild horses, deer and bison.
Finally the intensification of colonisation in the 19th century so diminished the forests that at present only 8% of the Ukraine is under timber, of which 23% is coniferous and 64.6% deciduous. The abundant wild life of the region has disappeared, the saiga antelope has retreated eastwards and only rodents, especially field mice and marmots, the plague of agriculture, are abundant. The loss of bird life has increased insect pests, though the locust which once did so much damage, has been exterminated. Destruc tive use of fine meshed nests, so that young as well as adult fish were caught, has markedly lessened the pike, tench, carp, crucian and shad in the rivers, and the sturgeon and sterlet which formerly swarmed up their lower courses are fast disappearing.