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The Water Cycle

© Don De Beyer

Water is one of the foundations of life on this planet. To the farmer, it can be the difference between a bountiful crop or plants withered and dead. Water is not just precipitation in the form of rain. In many areas, snowfall during the cold winter months can have a deciding factor in how subsequent crops do. For this reason, a clear understanding of the planets water cycle and the ramifications it causes is an important tool every farmer should utilize.

The majority of earth is in fact covered with water. Water in our oceans, ice caps, lakes, rivers and the ground all play important roles. With over 90% of our water in our oceans as salt water, fresh water is scarce and valuable. Only about 3 % of all water is fresh water. Of that most is unavailable for farming purposes as ice in Polar Regions and on glaciers. Thus only a very small amount of water is available in liquid, which is readily used by plants or animals.

Water is neither lost nor gained when you look at it on a planetary scale. It moves around by changing form (liquid, gas or solid) or becomes trapped in certain areas (plants, animals, ice etc). There are several names we give to this movement of water and they are evaporation, condensation, precipitation, transpiration, runoff and infiltration.

Evaporation is the process that occurs when a liquid (water) changes form into a gas or vapour. Evaporation occurs primarily from temperature and air pressure changes. More evaporation occurs on a hot clear summer day than a cold overcast one. During evaporation only water is evaporated while the impurities such as dirt remain.

Condensation is the opposite of evaporation. The water vapour in a gas is changed into a liquid. This usually occurs when the temperature of the water vapour is decreased. Very small droplets of water form clouds.

Precipitation is when these small droplets of water form into larger droplets. These large drops of water then fall to the earth as rain. Depending on temperature and pressure precipitation can also take the form of snow and hail.

Infiltration is the movement of water (rain, snow etc) that has fallen to earth and begins to move into the soil and rock. Infiltration only occurs when water is in its liquid state so temperature plays a part in the process. The earth is not flat and since water will flow downhill in some spots this causes water to exit the soil in low spots or as springs. Rocks can also restrict the downward movement of water. Water that remains in the ground is called groundwater.