Spatial and Seasonal Distribution of Rainfall and Runoff in Jamaica

Abstract

AVAILABILITY and use of water are vital concerns in developing countries. As these countries face a rapidly growing population, an unprecedented level of rural-urban migration, and an apparent rise in living standards, the demand for safe and reliable supplies of water, especially in the major population centers, has never been as intense as it is now. Additional demand on water supply is caused by irrigation, a necessary practice that must be adopted in many Third World countries in order to attain self-sufficiency in food production. A persistent problem in waterresource planning in these countries is the dearth of information on the amount of available water and on its spatial and seasonal distributions. This paper demonstrates a type of analysis on which discussion of water-supply management alternatives in one of these countries can be based. The study presents correlated information on rainfall and runoff in Jamaica. The first part of the paper looks at the distribution of rainfall over the island. In the second part, the streamflow characteristics are considered. The third section examines the relationship between rainfall and runoff. Jamaica, a developing Caribbean country of 2.1 million people, faces two important social and economic problems that have direct relevance to its water supply. The first is population pressure in major urban centers. The second is agricultural productivity. The government has introduced a variety of schemes designed to stimulate agriculture.' The success of these projects, however, depends in part on the availability of water for irrigation, because the most arable land is located in the drier sections of the island.2 The analyses presented in this paper are based principally on rainfall and streamflow data from eleven drainage basins (Table I). The basins include all major geographical regions in the island (Fig. 1). There are five north-flowing streams and six south-flowing ones. At least one stream originates or flows through the Blue Mountains, the Central Inlier region, the Cockpit Country, and the alluvial coast of the south. The data for these streams come from eleven of the thirteen parishes, or administrative divisions, of the island. Each stream had a daily flow record of at least fifteen years with an average record-length of eighteen years. The rainfall records were longer, an average of forty years. In preparing the map on distribution of runoff and runoff coefficients, use was made of short-term data with an average length of five years from ten additional stream-gauge stations. These stations were located on sections of some of the eleven streams, for example, Rio Cobre at Bog Walk, or on recently gauged streams such as the Yallahs River. The average rainfall for rainfallrunoff correlation analysis was obtained by isohyetal method. Three drainage basins were selected for an in-depth analysis of the relationship between rainfall and streamflow. They are the Rio Grande and the Black and Hope