Global precipitation is unevenly distributed due to a variety of factors including the pattern of global winds, the changing latitude of the location, and the presence of mountains. The volume of global precipitation is calculated by taking the product of the Earth's surface area and its average annual rainfall When the water droplets fuse to create large drops too heavy to be sustained in the air by air currents, they begin to fall as precipitation in a process known as coalescence. During the cooling process, the water vapor collects on condensation nuclei like dust particles which results in the formation of clouds. Precipitate forms as moist, warm air rises and cools. Precipitation is part of the hydrologic cycle and serves to bring water back down to the Earth. It can take on many forms such as rain, snow, or hail although the overwhelming majority occurs as rain. Precipitation is the product of any condensation in the atmospheric water vapor that reaches the surface of the Earth. 'The Control of the Water Cycle.' Scientific American. 'Annual average global precipitation is approximately 1123 mm (gauge corrections considered), which is consistent with other reported values. International Journal of Climatology 10(1990): 111-127. Mean seasonal and spatial variability in gauge-corrected, global precipitation. 'Because Earth's average annual rainfall is about 100 cm (39 inches), the average time that the water spends in the atmosphere, between its evaporation from the surface and its return as precipitation, is about 1/40 of a year, or about nine days.' 'The average annual precipitation of the entire surface of our planet is estimated to be about 1050 millimeters per year or approximately 88 millimeters per month.'Ĭlimate. Fundamentals of Physical Geography, 2nd Edition.

Precipitation totals by year