AS PART OF THE EARTH'S TOTAL HYDROLOGICAL CYCLE, HOW MUCH WATER EVAPORATES FROM THE EARTH'S LAND SURFACE EVERY YEAR?

You may be thinking, sure...rain falls.....then it rises again in many different forms, completing a circle that keeps planet Earth awash in water. But how much of it actually falls? And how much rises again? These are not easy questions to answer, but with a fair amount of research scientists have got an answer.

Most of the earth consists of water, there is much more water than there is land. About 70% of the earth's surface is covered in water. But water also exists in the air as vapor and in aquifers in the soil, as groundwater. The total water supply of the world is 1.400.000.000 km³. (A m³ of water equals 1,000 liters.)

Of the freshwater on Earth, about 2.200 km³ flows in the ground, mostly within half a mile from the surface. About 135.000 km³ of water can be found in the atmosphere as water vapor, in lakes, soil moisture, marshes and wetlands, rivers, plant and animals. Groundwater and fresh water stored in surface bodies and in the atmosphere represent an available resource of fresh water. Most of the freshwater is stored in glaciers and icecaps, mainly in the Polar Regions and in Greenland, and it is unavailable. This is another 24.500.000 km³ of water, forming the 69.5 % of the total fresh water of the Earth.

In the end it is estimated that each year, 119.000 km³ of water precipitates on land and 74.200 km³ evaporates into the atmosphere, by evapotranspiration from soil and vegetation. On ocean and sea surface 450.000 km³ of water falls every year and 502.800 km³ evaporates. According to hydrologists and climatologists, about 15,000 cubic miles of water may evaporate from the earth's land sources each year. This includes water that moves through growing plants as transpiration. This value is less than 20% of the water that evaporates from all the seawater sources on earth.