valleys determines the direction of the prevailing surface winds, this
being, however, subject to many local modifications. But it would
appear that throughout the year there is, with but slight interruption,
a steady upper current from the south-west, such as has been
already noticed over the Himalayas. The rainfall in the lower part
of the Irrawaddy valley, viz. the delta and the neighbouring part of
the province of Pegu, is very heavy; and the climate is mild and
equable at all seasons. But higher up the valley, and especially
north of Pegu, the country is drier, and is characterized by a less
luxuriant vegetation and a retarded and more scanty rainfall.
Within the boundaries of India almost any extreme of climate that is known to the tropics or the temperate zone can be found. It is influenced from outside by two adjoining areas. On the north, the Himalaya range and the plateau of Afghanistan Climate. shut it off from the climate of central Asia, and give it a continental climate, the characteristics of which are the prevalence of land winds, great dryness of the air, large diurnal range of temperature, and little or no precipitation. On the south the ocean gives it an oceanic climate, the chief features of which are great uniformity of temperature, small diurnal range of temperature, great dampness of the air, and more or less frequent rain. The continental type of weather prevails over almost the whole of India from December to May, and the oceanic type from June to November, thus giving rise to the two great divisions of the year, the dry season or north-east monsoon, and the rainy season or south-west monsoon. India thus becomes the type of a tropical monsoon climate. For the origin of the monsoon currents and their distribution see Monsoon.
The two monsoon periods are divided by the change of temperature, due to solar action upon the earth’s surface, into two separate seasons; and thus the Indian year may be divided into four seasons: the cold season, including the months of January and February; the hot season, comprising the months of March, April and May; the south-west monsoon period, including the months of June, July, August, September and October; and the retreating monsoon period, including the months of November and December. The temperature is nearly constant in southern India the whole year round, but in northern India, where the extremes of both heat and cold are greatest, the variation is very large.
In the cold season the mean temperature averages about 30° lower in the Punjab than in southern India. In the Punjab, the United Provinces, and northern India generally the climate resembles that of the Riviera with a brilliant cloudless The cold weather.sky and cool dry weather. This is the time for the tourist to visit India. In south India it is warmer on the west coast than on the east, and the maximum temperature is found round the headwaters of the Kistna. Calcutta, Bombay and Madras all possess the equable climate that is induced by proximity to the sea, but Calcutta enjoys a cold season which is not to be found in the other presidency towns, while the hot season is more unendurable there.
The hot season begins officially in the Punjab on the 15th of March, and from that date there is a steady rise in the temperature, induced by the fiery rays of the sun upon the baking earth, until the break of the rains in June. During this season the The hot weather. interior of the peninsula and northern India is greatly heated; and the contrast of temperature is not between northern and southern India, but between the interior of India and the coast districts and adjacent seas. The greater part of the Deccan and the Central Provinces are included within the hottest area, though in May the highest temperatures are found in Upper Sind, north-west Rajputana, and south-west Punjab. At Jacobabad the thermometer sometimes rises to 125° in the shade.
The south-west monsoon currents usually set in during the first fortnight of June on the Bombay and Bengal coasts, and give more or less general rain in every part of India during the next three months. But the distribution of the rainfall is The monsoon period.very uneven. On the face of the Western Ghats, and on the Khasi hills, overlooking the Bay of Bengal, where the mountains catch the masses of vapour as it rises off the sea, the rainfall is enormous. At Cherrapunji in the Khasi hills it averages upwards of 500 in. a year. The Bombay monsoon, after surmounting the Ghats, blows across the peninsula as a west and sometimes in places a north-west wind; but it leaves with very little rain a strip 100 to 200 m. in width in the western Deccan parallel with the Ghats, and it is this part of the Deccan, together with the Mysore table-land and the Carnatic, that is most subject to drought. Similarly the Bengal monsoon passes by the Coromandel coast and the Carnatic with an occasional shower, taking a larger volume to Masulipatam and Orissa, and abundant rain to Bengal, Assam and Cachar. The same current also supplies with rain the broad band across India, which includes the Satpura range, Chota Nagpur, the greater part of the Central Provinces and Central India, Orissa and Bengal. Rainfall rapidly diminishes to the north-west from that belt. A branch of the Bombay current blows pretty steadily through Rajputana to the Punjab, carrying some rain to the latter province. But the greater part of north-west India is served as a rule by cyclonic storms between the two currents. In September the force of the monsoon begins rapidly to decline, and after about the middle of the month it ceases to carry rain to the greater part of north-western India. In its rear springs up a gentle steady north-east wind, which gradually extends over the Bay of Bengal, and is known as the north-east monsoon. A wind similar in character, but rather more easterly in direction, simultaneously takes possession of the Arabian Sea. The months of November and December form a transition period between the monsoon and the cold season. The most unhealthy period of the year follows immediately after the rains, when malaria is prevalent, especially in northern India.
Unlike many other large geographical areas, India is remarkable for having no distinctive botanical features peculiar to itself. It differs conspicuously in this respect from such countries as Australia or South Africa. Its vegetation is in point of fact of a composite character, and is constituted by the meeting and more or less blending of adjoining floras,—those of Persia and the south-eastern Mediterranean area to the north-west, of Siberia to the north, of China to the east, and of Malaya to the south-east. Regarded broadly, four tolerably distinct types present themselves.
1. The upper levels of the Himalayas slope northwards gradually to the Tibetan uplands, over which the Siberian temperate vegetation ranges. This is part of the great temperate flora which, with locally individualized species, but often with identical Himalayas. genera, ranges over the whole of the temperate zone of the northern hemisphere. In the western Himalayas this upland flora is marked by a strong admixture of European species, such as the columbine (Aquilegia) and hawthorn (Crataegus Oxyacantha). These disappear rapidly eastward, and are scarcely found beyond Kumaon. The base of the Himalayas is occupied by a narrow belt forming an extreme north-western extension of the Malayan type described below. Above that there is a rich temperate flora which in the eastern chain may be regarded as forming an extension of that of northern China, gradually assuming westwards more and more of a European type. Magnolia, Aucuba, Abelia and Skimmia may be mentioned as examples of Chinese genera found in the eastern Himalayas, and the tea-tree grows wild in Assam. The same coniferous trees are common to both parts of the range. Pinus longifolia extends to the Hindu-Kush; P. excelsa is found universally except in Sikkim, and has its European analogue in P. Peuce, found in the mountains of Greece. Abies smithiana extends into Afghanistan; Abies webbiana forms dense forests at altitudes of 8000 to 12,000 ft., and ranges from Bhutan to Kashmir; several junipers and the common yew (Taxus baccata) also occur. The deodar (Cedrus Deodara), which is indigenous to the mountains of Afghanistan and the north-west Himalaya, is nearly allied to the Atlantic cedar and to the cedar of Lebanon, a form of which is found in Cyprus. A notable further instance of the connexion of the western Himalayan flora with that of Europe is the holm oak (Quercus Ilex), which is characteristic of the Mediterranean region.
2. The north-western area is best marked in Sind and the Punjab, where the climate is very dry (the rainfall averaging less than 15 in.), and where the soil, though fertile, is wholly dependent on irrigation for its cultivation. The flora is a poor one inNorth-west. number of species, and is essentially identical with that of Persia, southern Arabia and Egypt. The low scattered jungle contains such characteristic species as Capparis aphylla, Acacia arabica (babul), Populus euphratica (the “willows” of Ps. cxxxvii. 2), Salvadora persica (erroneously identified by Royle with the mustard of Matt. xiii. 31), tamarisk, Zizyphus, Lotus, &c. The dry flora extends somewhat in a south-east direction, and then blends insensibly with that of the western peninsula; some species representing it are found in the upper Gangetic plain, and a few are widely distributed in dry parts of the country.
3. For the Malayan area, which Sir Joseph Hooker describes as forming “the bulk of the flora of the perennially humid regions of India, as of the whole Malayan peninsula, UpperAssam and Malayan peninsula. Assam valley, the Khasi mountains, the forests of the base of the Himalaya from the Brahmaputra to Nepal, of the Malabar coast, and of Ceylon,” see Assam, Ceylon and Malay Peninsula.
4. The western India type is difficult to characterize, and is in many respects intermediate between the two just preceding. It occupies a comparatively dry area, with a rainfall under 75 in. In respect to positive affinities, Sir Joseph HookerWestern India. pointed out some relations with the flora of tropical Africa as evidenced by the prevalence of such genera as Grewia and Impatiens, and the absence, common to both countries, of oaks and pines which abound in the Malayan archipelago. The annual vegetation which springs up in the rainy season includes numerous genera, such as Sida and Indigofera, which are largely represented both in Africa and Hindustan. Palms also in both countries are scanty, the most notable in southern India being the wild date (Phoenix sylvestris); Borassus and the coco-nut are cultivated. The forests, though occasionally very dense, as in the Western Ghats, are usually drier and more open than those of the Malayan type, and are often scrubby. The most important timber trees are the tún (Cedrela Toona), sál (Shorea robusta), the present area of which forms two belts separated by the Gangetic plain; satin wood (Chloroxylon Swietenia), common in the drier parts of the peninsula; sandal-wood, especially characteristic of Mysore; iron-wood (Mesua ferrea), and teak (Tectona grandis).
