1. Introduction 1.1 Hydrological Cycle a schematic view of the global hydrologic cycle is shown in Figure 1. 1. This diagram shows the interactions and mass transfers (water in different states) that occur between the atmosphere land surfaces and oceans "气 只z"z月0 Figure 1 SChematic diagram of hydrologic cycle(from Bear and Verruijt, 1987)1. Introduction 1.1 Hydrological Cycle A schematic view of the global hydrologic cycle is shown in Figure 1.1. This diagram shows the interactions and mass transfers (water in different states) that occur between the atmosphere, land surfaces, and oceans. E T = Evapotranspiration; E = Evaporation; I = Infiltration; SR = Surface runoff; R F = Return flow from irrigation; N = Natural replenishment. Figure 1.1Schematic diagram of hydrologic cycle (from Bear and Verruijt, 1987) 1