These figures, showing a great range of temperature in regions of prolonged winter, indicate what a dislocation the brief spring brings to the life of Russia and how great is the strain on plant, animal and human life to secure adaptability. In European Russia the last days of frost are experienced for the most part in April, but north of lat. 55° N. in May and progressively later towards the north. In Asiatic Russia spring sets in at the end of April in the south and progressively later towards the north. Thus on a line from Yakutsk, passing north of Beresov on the Ob, south of Mezen and through Kola the average date of thawing on the rivers is May 21st. On a line extending from Sredne Kolimsk through the confluence of the Butyntai and Yana rivers, bending south over the plateau and turning north to Obdorsk the date is May 31st; on the upper Lena and its delta and at the mouth of the Yenisei, the thaw does not set in until the second week in June. The date of freezing of rivers in Russia varies from De cember near the north coast of the Black Sea, and for the northern part of the Caspian and the Sea of Aral to November on the northern coast.
In Asiatic Russia the date of freezing varies from November in the south to September for the Taimyr peninsula and the region east of Yana Bay. We thus have a picture of an unlocking of the winter grip setting in about April in the south and at dates vary ing from early May in the west to late June in the north-east, with a period of possible vegetation activity at its maximum in the south-west and rapidly diminishing towards the north-east. The melting of the snows and the consequent flooding of the roads and river banks and the coming of the spring rains, slight though their quantity may be, disorganise traffic. The badly constructed roads become seas of mud, the frozen marshes turn to quaking bogs and the rivers are at first obstructed by blocks of ice. On the lower courses of the rivers flowing to the Arctic blocks of ice brought by the warmer water from the earlier thawing upper courses are heaped upon the still frozen river, and as this latter melts and begins to flow the banks are flooded and ice blocks are carried on to the land to the accompaniment of deafening crashes of the great blocks as they are hurled against one another.
A set-back to spring occurs in the second half of May, most sharply felt in Siberia, where the "icy saints' days," as they are called, are so blighting that it is impossible to cultivate the apple and the pear. This return of frost is experienced fre quently in the Ukraine in a belt lying south of the extension of high pressure. Northerly and easterly winds may bring such biting frost that the leaves of the oak are shrivelled in an hour or two. It is significant to note that the maximum pressure condi tions of April in the Polar region are succeeded by minimum pres sure conditions in June. (This phenomenon of late spring frosts
is by no means confined to Russia.) Precipitation.—Evaporation from melting snows and dry ing surfaces keeps the spring temperature lower than the autumn temperature except in Turkestan and the steppes to the north of it, where snow does not lie because of the exposure of this treeless region to violent winter winds. In these regions, there fore, in accordance with the greater spring altitude of the sun, spring is warmer than autumn. The snow covering is thickest in the taiga belt (often 3 ft.) and in the west, under the influence of occasional cyclones, may form drifts of very great depth. The thin snow covering of Asiatic Russia melts in spring. Except in the extreme north of European Russia, in the deserts and steppes east of the Caspian roughly south of lat. 48° N., and in trans-Caucasia and the east coast strip of the Black Sea, summer is the season of maximum precipitation. The Pacific coastal strip, under the influence of the south-east monsoon has a particularly wet, stormy, cool summer unfavourable to agriculture, the maxi mum fall being in August. In Asiatic Russia east of the Yenisei and in the northern part from the west of the lower Yenisei to the Urals July and August are the rainiest months, a condition unfavourable to grain crops.
In a belt lying north of the steppe-desert and of the Caspian, east of a line curving through Astrakhan, Kazan and Bogo slovsk, and stretching west to the Altai, June and July are the wettest months. This belt terminates south of lat. 6o° N. in the west and north of it in the east. To the west of it June is the wettest month in the south and August in the north, while in the central and western zone beyond, July is the month of greatest rainfall. To the north of this region July and August are the wettest months. Thus in many regions a wet August follows a severe winter. Winter rainfall is kept at a minimum by the prevalence of outblowing winds from the dry high pressure area, but in summer pressure conditions are reversed. Autumn, with its transition to the frost regime, is, like spring, a season of in terruption of communications both by road and river, sometimes involving interruption of telegraphic communication because of the impossibility of getting over the roads to carry out repairs. Precipitation except near the Caucasus range and the coastal range of the east against which the south-east monsoon impinges, Is fairly uniform, averaging about 20 inches in the central belt west of the Urals and 15 inches in that belt east of the Urals extending to the Pacific coastal ranges. Regions with such a rain fall may be humid in conditions of minimum evaporation, espe cially if the soil is clayey or icebound ; they are arid in conditions favouring evaporation and dispersion of soil moisture.