Mapping the Unequal Distribution of Global Precipitation – On average, nearly one meter (39 inches) of rain or snow falls on the Earth in a year. However, differences in latitude, winds, changes in the Earth’s surface, and the planet’s tilt, make for an unequal distribution of global precipitation. Cartographer Perrin Remonté uses data from Chelsea Climate to visualize this by splitting the world in two. One half, in blue, receives more than one meter of rain (or snow) in a year, the other half receives less. What Affects Global Precipitation Patterns? From the water cycle we know that precipitation starts with evaporation. However, moist air needs to cool and then condense to come down as rain (or snow). Below we list some major factors influencing precipitation.

• Proximity to water: Oceans and lakes provide a constant source of moisture.
• Lower latitudes: Areas at, or close to the equator, are hotter and this can increase evaporation from nearby water bodies.
• Topography: Mountain ranges, especially along coasts, force warm air to rise and cool, resulting in rain or snow on the windward side and dry rain shadows on the lee side.
• Trade winds: Persistent, easterly surface winds blow from subtropical high-pressure areas toward the equator, carrying moist air from the ocean to the land.