By R.A.L.H. Gunawardana
Past and Present, Vol.53:1 (1971)
Introduction: For more than fifteen centuries, the centres of political and cultural activity of the people of Ceylon were located in the region which is generally termed the Dry Zone. The exact definition of the Dry Zone is still a subject of controversy. But, in practical terms, it is clearly distinguishable today from the rest of the land area of Ceylon by differences in the intensity and seasonal pattern of rainfall, vegetation and in the density of population. The greater part of this region receives a mean annual rainfall of fifty to seventy-five inches, which, though not meagre in a comparative sense, tends to be concentrated within a few months of the year. In this whole region, which covers about seventy per cent of the total land area of the Island, only the Jafina peninsula and a stretch of land in the northwestern coastal belt with water-retentive limestone rock-strata afford scope for extensive well irrigation. The rest of the Dry Zone has a substratum of crystalline rock with very poor water-retaining qualities.’ Radial streams discharge the water from the rains into the sea in a very short time; and apart from the Dfiduru Oya and the Valave Ganga which flow along the outer limits of the Dry Zone on the west and the south respectively, only one river in this region, the Mahavali Ganga, maintains a continuous flow throughout the year. Available evidence suggests that the climatic conditions were basically similar to the present in the period up to the thirteenth century which saw the height of efflorescence of hydraulic civilization in Ceylon. The response of the Sinhala civilization to this challenge from climatic conditions is evident today in the ruins of the ingenious irrigation system of ancient and medieval Ceylon which was unique in the whole of South Asia in both its scale and the technological ability it displayed.