Chapter 16 Fresh water resources 16 Fresh Water Resources Saline water in oceans: 97.29 Ice caps and glaciers: 2. 14% Available fresh water: 0669 Fresh water is a limited source
Chapter 16 Fresh water resources Fresh water is a limited source
16. 1 Water circulates through the hydrologic cycle (水文循环) The Earth's water is constantly circulating powered by the heat of the sun and the force of gravity Water evaporated from ocean precipitates(降水) into the ocean direct route Water evaporated from ocean is blown by winds until it is over the land and precipitates:(1 evaporates beck into atmosphere, (2). Infiltrate the ground, (3 ). Become part of the snow or glacier,(4). Drain to a river and back to the sea
16.1 Water circulates through the hydrologic cycle （水文循环） • The Earth’s water is constantly circulating, powered by the heat of the sun and the force of gravity. • Water evaporated from ocean precipitates (降水) into the ocean: direct route. • Water evaporated from ocean is blown by winds until it is over the land and precipitates: (1) evaporates beck into atmosphere, (2). Infiltrate the ground, (3). Become part of the snow or glacier, (4). Drain to a river and back to the sea
Precipitation Precipitation Evaporation EVaporation Runo Ocean Land 3 Infiltrate Figure 16.1 The hydrologic cycle Water evaporated at the earth s surface enters the atmosphere as water vapor, condenses into clouds, precipitates as rain or snow, and falls back to the surface, only to go through the cycle yet another time
Water table(地下水位) 热 W Normal water table Stream Water table during drought Figure 16.2 The water table in any location roughly parallels surface contouring. In times of drought, the water table falls, reducing stream flow and drying up wells. It also falls when the amount of water pumped out of a well exceeds the amount replaced as precipitated water infiltrates the ground and recharges the supply
Water table (地下水位)
Ground water and surface water Over-use of ground water leads to subside(沉降) of land H H Figure 16.3 The Leaning Tower of Pisa, built cen- turies ago, slowly acquired a deviation from the vertical of about 4.6 meters as a result of groundwater withdrawal The towers foundation has been sta- bilized by groundwater withdrawal management and the tower should remain stable for years to come
Ground water and surface water • Over-use of ground water leads to subside (沉降) of land