Rainfall Rainfall. Image via the Herald. ZIMSEC O Level Geography Notes: Rainfall. Rainfall is just one form of precipitation. Precipitation occurs when warm moist air rises or is forced to rise. Water vapor in the air parcel cools and condenses to form clouds. This is because temperature falls with increase in altitude. When condensation occurs it produces minute droplets of less than 0.05mm in diameter. When these droplets join together and grow to fall of their own weight it is called rain. There are other forms of precipitation besides rain such as sleet, hail, dew, hoar frost, fog and rime and snow. Types of rain There are various types of rain depeding on how the air rises/ is forced to rise these are: Frontal/CyclonicOccurs along fronts when air e.g S.Western Cape in South Africa.Click here to read more about frontal rainfall. Relief/OrographicOccurs when warm air is forced to rise by mountains.Click here to read more about Relief rainfall ConvectionalOccurs when the air adjacent to an excessively heated ground rises.Click here to read more about convectional rainfall ConvergenceOccurs along the ITCZ.Click here to learn more about convergence rainfall Other types of precipitation 1. Sleet Sleet falling image by Pixshark A mixture of snow and rain. Usually formed by snow melting as it falls. 2. Hail A hailstorm. Image via Riverfronttimes. A solid form of precipitation. It consists of balls of irregular lumps of ice falling from the sky each of which is called a hailstone. When large chunks of ice falling from the sky it is referred to as a hailstorm. 3. Dew Dew in the morning. Image by UK Met Office Dew is the small droplets of water that appear on objects such as leaves or grass in the morning or evening due to processes of condensation. Dew forms when the temperature of a surface cools down to a temperature that is cooler than the dew point of the air next to it. The temperature at which droplets form is called the dew point. 4. Hoar Frost Hoar Frost. Image via DevianArt. Frost is the coating or deposit of ice that may form in humid air in cold conditions, usually overnight. Is common in places like Nyanga, Marondera and some parts of Harare in winter. 5. Fog/Mist Fog. Image via MediaWiki. It is a visible mass consisting of cloud water droplets or ice crystals suspended in the air at or near the Earth’s surface. Fog can be considered a type of low-lying cloud, and is heavily influenced by nearby bodies of water, topography, wind conditions, and even human activities. Fog reduces visibility to less than 1 km while in a mist visibility is reduced to between 1 and 2 km. 6. Rime Rime. Image by MediaWiki is a white ice that forms when the water droplets in fog freeze to the outer surfaces of objects. Often seen on trees. 7. Snow Snow. Image by Crossvillenews. is precipitation in the form of flakes of ice particles that fall from the clouds. Snow does not occur in Zimbabwe although it is common in countries like the UK during winter. 8. Drizzle Drizzle. Image by Gothamgirlchronicles. Very fine rain. Usually falls from layers of cloud that have very limited vertical development e.g stratus clouds. Go to Geography Notes Home to access more topics.