The World Hydrological Cycle

Abstract

This chapter considers water in the global context with some figures to illustrate the storage capacity of the earth-atmosphere system. The storage figures for atmospheric and continental water are percentages of all fresh water. Evaporation provides the moisture input into the atmospheric part of the hydrological cycle and may be taken as our starting-point. The atmospheric moisture content, comprising water vapour and water droplets and ice crystals in clouds, is determined by local evaporation, air temperature, and the horizontal atmospheric transport of moisture. The major types of precipitation are drizzle, rain, snow, and hail, although dew, fog drip, hoar frost, and rime may also make significant contributions to the total. Water circulation in the atmosphere and oceans is intimately linked with the global energy budget. The interdependence of the various components of the hydrological cycle makes it apparent that a change in any climatic parameter may have far-reaching repercussions.