Precipitation is the overall term for all types of water that fall to the earth, whether as rain, dew or thaw. To do this the water must enter the atmosphere first.

Oceans are the greatest water reservoirs of the earth and therefore the largest source for evaporation of water. That is how humidity comes about. Because water in a vapor-like condition is lighter than air it rises upwards. However, the upper part of the atmosphere is significantly colder. So the water condensation condenses and forms clouds. These are now driven over the water and land by the wind until additional conditions such as mountains or colder layers of air make it impossible for the clouds to hold the water, which is then ejected. That is how precipitation comes about.

The type of precipitation depends on the temperature in the environment. When the temperatures are significantly above freezing the precipitation becomes rain and when the temperatures are below freezing it snows. When it is approx. 0° there is often a mixture. Under certain conditions there can be ice rain, black ice, ice pellets, sleet or hail.

Aside from the precipitation as rain dew or frost can occur. When it does it means that the precipitation has made the detour around ocean or clouds. Dew occurs when the air has cooled down to such an extent that it is below the dew point and the water it contains condenses. This generally occurs in the early morning hour as that is when the temperatures are the lowest and the air can store less water. The dew point for frost is so low that the water vapor freezes immediately and settles near the ground in the form of ice.

Precipitation is measured with special rain gauges or special devices. It is just as easy to measure snow and hail by warming the rain gauge causing the snow and hail to melt. Data that is supplied by a precipitation radar or weather satellite is used to predict the amount of rain to be expected for large areas. Usually the amount of precipitation is measured in liters per square meter. If one takes account of the landscape sealing it can be predicted whether certain regions are at risk.

It has become very important to be able to predict precipitation, not only perils such as hail, snow or ice rain. These predictions are also used to warn of floods. It has special significance for agriculture which makes it possible to forecast irrigation or harvesting dates and thus providing a positive impact on the harvest result.