Portugal - Atlas do Ambiente I.4 - Precipitação

Summary

Water in any form, liquid or solid, falling from the atmosphere and reaching the ground, is said to be precipitation. The most significant types of precipitation are: drizzle and rain in liquid form, and snow, ice pellets and hail in solid form. Precipitation, in liquid and solid forms, is said to occur as showers when it falls from convective clouds and occurs by short periods beginning and ending suddenly. The amount of precipitation which reaches the ground in a stated period of time is measured in millimetres with raingauges; the millimetre expresses the depth to which a litre of liquid water covers a horizontal surface of a square metre, ifthereis no loss by evaporation, runoff or infiltration. Rainfall intensity is the rate of precipitation, usually expressed in millimetres per hour. If the rate of precipitation is of a millimetre per hour, or more, the rain is said to be heavy rain. If the precipitation occurs as showers ata rate of fifty millimetres per hour, the showeris saidto be a heavy, ora violent, shower. Climates may be classified according to the annual or seasonal amount of precipitation. Precipitation is generally conditioned by latitude and altitude, together with mechanisms which: produce rainfall, as low centres or depressions, frontal systems, convectives motions, etc. 6