Water is evaporated by the sun from lakes, ponds, soils and vegetation, it rises into the sky where it condenses and falls back as rain, snow, or dew then becomes available to the biosphere.
Over the world the evaporation and precipitation of water is in balance, although evaporation exceeds precipitation over the oceans and the opposite over the land. Only about 5 percent of the earth’s total water is in circulation through the hydrosphere and 95 percent is bound up in the lithosphere (the region if the earth composed of rocks). It takes a water molecule about ten days to be transported through the atmosphere before precipitation takes place.
Plants and animals respond to a combination of water, temperature, and light. The high temperatures and sunlight there is higher transpiration rates from plants, and high evaporation rates from the soil, lakes and oceans. The rate of water loss from any surface depends in particular on the energy exchange with at surface by radiation and convection.
The community of plants and animals present in the ecosystem depends on the availability of water.
The continuing modification by humans of the global hydrological cycle can have serious consequences on climate, and therefore will affect life as we know it.
(figure available in print form)